Published: January 20, 2023

This chapter provides guidance for elements of design that are common to a wide range of pedestrian and bicycle facility types. These include design speed, sight distance, physical and operating width, alignment elements, and other considerations such as utilities, landscaping, and surface treatments.

Multimodal facility design controls are based on the physical and operating characteristics of various types of pedestrians and bicyclists and the vehicles and mobility devices they use to get around (see Table 3-13). Additionally, the interactions between users of shared facilities, such as shared use paths, must also be considered in the design. The pedestrian and bicycle physical characteristics include the user profile, size of the person and bicycle, and eye height, while the operating characteristics include the speed, reaction time, and braking ability.

Other elements of design that are important to the safe travel of people walking and bicycling include lighting, drainage, surface quality, placement of utilities and landscape elements, and geometric design strategies to reduce the number and severity of crashes at crossings. This chapter and later chapters discuss these common elements of design.

3.1 Design Flexibility and Engineering Judgement

Designers have significant flexibility making decisions regarding roadway design criteria. As defined by FHWA in its 2013 guidance memorandum, Bicycle and Pedestrian Facility Design Flexibility,1 FHWA supports a flexible approach to bicycle and pedestrian facility design, including the use of multiple national guides and resources, such as those published by AASHTO, the National Association of City Transportation Officials (NACTO), and Institute of Transportation Engineers (ITE), to inform bicycle and pedestrian facility designs. FHWA explicitly “encourages agencies to appropriately use these guides and other resources to… go beyond the minimum requirements, and proactively provide convenient, safe, and context-sensitive facilities that foster increased use by bicyclists and pedestrians of all ages and abilities, and utilize universal design characteristics when appropriate.”

Moreover, the AASHTO “Green Book” recommends a design process that encourages greater flexibility in design for all roadway projects, particularly for projects on existing roads. The goal is to address community and multimodal needs rather than to adjust existing roadway design features to meet nominal design criteria, if doing so is not necessary to address a documented safety need.

ODOT recognizes the need for flexibility in design. The preface in the L&D Manual Volume 1 states that designers must understand the context and the constraints of their project when selecting design criteria. L&D Manual Volume 1 describes the Performance-Based Project Development (PBPD) strategy that, like AASHTO, highlights the need to establish a Purpose and Need for a project and then evaluate options and design deviations that meet that Purpose and Need. The premise is that the proposed improvements should be targeted and right-sized based on project-specific needs. The guidance provided in the MDG allows for flexibility by providing a range of values for most design criteria and including information for decision-making throughout the design process. Design flexibility is interrelated with PBPD, as both concepts make engineering decisions through an application of data, analysis, and engineering judgement.

Design flexibility should be used to prioritize the safety, comfort, and connectivity of people walking and biking. Applying design flexibility to multimodal design projects is not strictly defined and may require more conversations, considerations, exploration, and collaborating to develop answers to challenging design questions.

Common performance-based multimodal alternatives include fewer motor vehicle lanes (e.g., road diets) to provide space for bicyclist and pedestrian facilities, narrow lane widths where target motor vehicle speeds are low to enhance safety of all road users (especially pedestrians and bicyclists), and smaller corner radii to reduce the speeds of turning motorists where they conflict with pedestrians and bicyclists.

Documentation

When applying design flexibility, it is important to follow and document a clear process to determine the appropriate application of, or deviation from, design guidance in order to reach the solution. When implementing design decisions that are within the range of allowable values, but that perhaps use a higher than minimum value, these decisions should still be documented. All relevant design information, such as the selection of design user, design width selection, and others, should be documented in the project file.

3.2 Design Users

People who walk and bike are influenced by how comfortable they are using the street. The provision of low-stress, connected multimodal networks often improves a user’s safety and accommodates walking and biking for a broader range of people. Often, when more people bicycle and walk, there is an increase in the safety of these user groups; this effect is commonly referred to as “safety in numbers.”^2,3,4 The presence of more pedestrians and bicyclists encourages motorists to look for these street users where they are prevalent. As such, designing for the widest range of users will best accommodate the majority of users.

To design a multimodal transportation system that works for all people, the design process must account for basic factors such as safety and comfort, as well as human factors such as a person’s physical abilities, experience, and their ability to perceive and react to potential conflicts.

In addition to the people navigating the system, it is necessary for designers to pay close attention to the mobility devices that users employ. Tools that enable or aid personal movement have physical and dynamic characteristics that should be considered in the design of the street. This focus on how people get around is the basis for identifying the design user profiles that inform key elements of design.

3.2.1. User Profiles

The design user profile varies based on the person’s age, comfort, experience, skill, and abilities. It includes people who are familiar or unfamiliar with the area, and therefore the idea of “expectancy” is important to consider. User experiences develop over time and form a set of expectations, which allow the person to anticipate and plan for future events. This set of expectations is what enables people to respond to common situations in predictable and safe ways.

Designers should understand that a person’s design profile may change in a single day. For example, a person who walks or bikes to work daily might be comfortable using a large arterial street with standard width sidewalks and bike lanes when traveling alone, but when traveling with children they may prefer to use lower volume or lower speed streets that have wider buffers from traffic, wider sidewalks, or a shared use path.

Pedestrians

There is no single “design pedestrian.” Considerations when selecting facilities include walking and jogging speeds, spatial requirements, and mobility needs. The AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities provides details on these elements.

Designers should understand that pedestrians display a wide range of physical, cognitive, and sensory abilities. If a design works well for people with disabilities, it generally works well for those who do not have disabilities. It should be noted that disabilities are not a special condition of the few, but are ordinary occurrences that affect most people for at least some part of their lives. When facilities are designed for people of all ages and abilities, the transportation network can begin to safely and conveniently get everyone where they need to go.⁵

Designers should consider seniors and children, who typically walk slower, as the preferred user profile when assessing street crossings. A crossing that accommodates these slower users will naturally accommodate faster users. A person jogging should be considered as the preferred user profile when assessing sight distances for driveway crossings, the intersection of sidewalks and shared use paths, or other locations where pedestrians are not expected to yield to motorists or bicyclists. Designing sight distances for these faster users will naturally accommodate the slower pedestrian facility users. See Section 3.3 for design speeds.

People Bicycling

Of adults who have stated an interest in bicycling, research has identified three types of potential and existing bicyclist profiles (see Figure 3-1).6 These bicyclist profiles consider a person’s comfort level operating a bicycle with motorized traffic, bicycling skill and experience, age, and trip purpose. These user profiles can be used to inform bikeway design.

The Interested but Concerned Bicyclist profile should typically be used to choose a bikeway design, as this group represents 51 to 56 percent of the general population and is the largest of the bicyclist profiles. Members of this group bicycle less in many communities due to a lack of connected, low- stress bicycle networks; for the same reason, this group tends to bicycle more for recreation and is less comfortable riding for transportation. To maximize the potential for bicycling as a viable transportation option, it is important to design facilities to meet the needs of the Interested but Concerned Bicyclist user, which will also naturally accommodate the Somewhat Confident and Highly Confident users.

Figure 3-1: Bicyclist Design User Profiles

Designers should consider all likely users of a bicycle facility when establishing the various design controls. Common exceptions to using the adult bicyclist to establish design controls are:

• Using performance criteria associated with a pedestrian at street crossings where pedestrians will be crossing with bicyclists. This is common at shared use paths and at some bicycle boulevard crossings, which must be designed to ensure a pedestrian can safely cross the road at a typical walking speed.
• The heights and speeds of recumbent bicyclists or child bicyclists for the purposes of establishing sight distances or crossing times at intersections.
• Using a bicyclist pulling a trailer for the purposes of designing median crossing islands or queuing areas.

The performance characteristics of the typical adult bicyclist should generally be used to establish many geometric design controls because the adult bicyclist is typically the fastest and physically largest user. Table 3-1 summarizes factors that may impact bicycling, such as acceleration, deceleration, and reaction time. The use of these values will generally ensure bicyclists of all abilities are accommodated on bikeways and roadways, but the context and expected use should also inform design decisions. For example, a shared use path with low pedestrian activity expected to be used for recreational bicycling may be a location where higher bicyclist design speeds are appropriate. See Section 3.3 for design speeds.

Table 3-1: Typical Adult Upright Bicyclist Performance Characteristics

3.2.2. Devices

Some of the types of devices that are commonly used on Ohio streets and trails are shown below in Figure 3-2. Typical variations in height, width, and length are noted. Although recommended facility widths for bike lanes, shared use paths, and sidewalks in the MDG generally address these devices, designers should be cognizant of the expected use of the longest and widest devices and should provide appropriate accommodations for the use of these devices.

Figure 3-2: Summary of Expected Design Vehicles and Dimensions

3.3 Design Speeds

Design speed is a fundamental design control used to determine various geometric features of a roadway or shared use path as well as some signal timing and street crossing parameters. Motor vehicle design speed consideration in multimodal design is discussed in Chapter 7 of this guide. Additional details for how speeds relate to the design of pedestrian and bicycle facilities is provided in Chapters 4, 5, and 6.

3.3.1. Pedestrians

Pedestrian speeds can vary based on physical ability, mobility devices used, age, and trip purpose, and in most cases range from 1 to 4 ft/s. 3.5 ft/s is the default assumed pedestrian design speed under most circumstances. 7.5 ft/s should be used as the assumed jogging speed of a pedestrian. These speeds are primarily used for determining pedestrian clearance intervals at signalized intersections but are also used for determining sight distances at some uncontrolled crossings. Additional information about accessible pedestrian signal design is available in the OMUTCD and Chapter 8. The OMUTCD provides for an extended pedestrian signal phase at accessible pedestrian signals and longer standard pedestrian signal phase lengths, which depend on the expected pedestrian speeds in a given intersection location.

The use of mobility devices can also affect walking speeds, and speeds can vary for people with disabilities, as shown in Table 3-27. Designers should consider the frequency of users with mobility devices and disabilities and adjust design speeds accordingly.

Table 3-2: Mean Walking Speeds for Disabled Pedestrians and Users of Various Assistive Devices

Source: Human Factors in Traffic Safety

3.3.2. Bicyclists and Micromobility Users

Design speed is the speed used for the design of various geometric features of bicycle/micromobility facilities and street crossing parameters. It is important for designers to recognize that, similar to design for automobiles, the design speed for a bicycle facility should be set at the desired user speed, not necessarily the speed that a bicyclist or micromobility user is physically capable of achieving.

Bicycle design speed can range from 8 mph to 30 mph depending on the facility type and expected design user. By comparison, most micromobility devices have a maximum speed of 15 mph. The following values should be considered for the design speeds of different bicycle facility types:

• 15 mph on separated bikeway and high-volume shared use paths
• 18-30 mph on low-volume shared use paths (where peds < 30 percent)
• 15-20 mph on bicycle boulevards
• Posted speed for on-road facilities (though typically ≤ 30 mph)

Designers should consider the context of the facility and identify the appropriate design speed for the project. For example, a long-distance, low-volume shared use path may have a higher design speed between destinations, but it also may travel through higher-volume areas where either greater widths, separation between bicyclists and pedestrians, or lower design speeds may be appropriate.

3.4 Understanding Mutual Yielding

There are three key factors that should be considered when designing interactions between bicyclists, motorists, and pedestrians:

1. Motorists and bicyclists have a legal responsibility to yield to pedestrians in crosswalks. [ORC 4511.46 Right-of-way of pedestrian within crosswalk [A]]
2. Ohio Revised Code stipulates that a pedestrian may not suddenly leave any curb (or refuge median) and walk or run into the path of a vehicle that is so close that it is impossible for the motorist to yield. [ORC 4511.46 Right-of-way of pedestrian within crosswalk [B]]
3. Motorists have the legal responsibility to exercise due care to avoid colliding with any pedestrian or bicyclist. [OPC 4511.46 Right of Way of rule at through highways, stop signs, yield signs and ORC 4511.13 Highway traffic signal indications]

The result is a mutual yielding responsibility among motorists, bicyclists, and pedestrians, depending upon the timing of their arrival at an intersection. When designing intersections between pedestrian facilities and roadways, bikeways and roadways, or bikeways and pedestrian facilities, designers should understand the application of traffic control devices to communicate right of way and the laws regarding assignment of right of way for pedestrians and bicyclists (and other bicycle facility users).

The effectiveness of mutual yielding is dependent on the ability of each user to see and react to each other, which relies on providing clear sight lines between users (see Section 3.5), use of appropriate traffic control to communicate right of way, and sufficient lighting.

3.4.1.  Zones: Recognition, Decision, Yield/Stop

In the case of permissive vehicular right and left turns across a bikeway, a turning motorist should yield to a through bicyclist unless the motorist is at a safe distance from the bicyclist to complete the turn at a reasonable speed prior to the bicyclist arriving at the conflict point. Bicyclists should yield to motor vehicles already within the intersection or so close that it is impossible to stop. Bicyclists and motorists must yield to (or stop for) pedestrians within a crosswalk. To facilitate these responsibilities, adequate sight distances and sight lines are needed between bicyclists, motorists, and pedestrians as they approach intersections. Motor Vehicle sight distances should conform to sight distances established in Section 3.5 and L&D Manual Volume 1, Sections 200.

For all bikeway and pedestrian crossings, a design objective is to provide adequate sight distances and sight lines for each user to detect a conflicting movement of another user and to react appropriately as they approach a conflict point. The approach to a conflict point is composed of three zones:

1. Recognition zone - the approaching bicyclist, motorist, or pedestrian has an opportunity to see the other user(s) and evaluate their respective approach speeds.
2. Decision zone - the bicyclist, motorist, or pedestrian identifies who is likely to arrive at the intersection first and adjusts their speed to yield or stop if necessary.
3. Yield/stop zone - a space for the motorist or bicyclist to yield or stop, if necessary.

At intersections with permissive turning movements where bicyclists and motorists are traveling in the same direction, there are two scenarios that occur depending upon who arrives first at the crossing. The ability for each user to respond accordingly is dependent upon the provision of the three zones mentioned above and depicted in Figure 3-3. The two yielding scenarios are:

• Turning Motorist Yields to (or Stops For) Through Bicyclists - This scenario occurs when a through moving bicyclist arrives or will arrive at the crossing prior to a turning motorist, who must stop or yield to a through bicyclist and pedestrians. For locations where bicyclists are operating on separated bike lanes and side paths, vertical elements near the intersection, including on-street parking, should be set back sufficiently for the motorist to see the approaching bicyclist and provide sufficient time to slow or stop before the conflict point.
• Through Bicyclist Yields to (or Stops For) Turning Motorist - This scenario occurs when a turning motorist arrives or will arrive at the crossing prior to, or at the same time as, a through moving bicyclist. This scenario can also occur when a bicyclist approaches after a motorist has yielded to other people crossing in the intersection and the crossing is clear for the motorist to proceed. The motorist may begin turning as the bicyclist approaches, requiring the bicyclist to slow and potentially stop while the motorist completes the turning movement.

Figure 3-3: Example of Mutual Yielding Zones Illustrating Intersection Sight Distance Case A

3.5 Sight Distance

The basic ability to see what lies ahead and to see intersecting users is fundamental to pedestrian and bicyclist safety, regardless of the facility type. Adequate sight lines and sight distances are needed to enable people walking, bicycling, and driving to slow, stop, or maneuver to avoid a conflict at all locations where they interact (e.g., street and roadway intersections, driveways, and alleys). Adequate sight lines should also be provided between bicyclists and pedestrians where they interact at crosswalks, intersections, bus stops, and other conflict areas.

3.5.1. Stopping Sight Distance

Adequate motor vehicle stopping sight distance is important for the safety of pedestrians and bicyclists who must cross roadways. Refer to L&D Manual Volume 1, Section 201.2 for procedures for determining motor vehicle stopping sight distances.

Bicycle stopping sight distance is the distance needed to bring a bicycle to a fully controlled stop. It is a function of the user’s perception and brake reaction time, the initial speed, the coefficient of friction between the wheels and the pavement, the braking ability of the user’s equipment, and the grade. Table 3-3 provides the formula for minimum stopping sight distance. A perception/reaction time of 2.5 seconds should typically be used to calculate stopping sight distance, though 1.5 seconds may be appropriate where bicyclists have an expectation of potential conflicts, such as approaching intersections or in urban areas. The sight distance for bicyclists should typically be measured from 3.83 ft. above the ground to accommodate recumbent bicyclists.

Table 3-3: Minimum Stopping Sight Distance

Note: + = negative traveling downhill, positive uphill

Table 3-4 and Table 3-5 indicate the minimum stopping sight distances based on speed and grade for 2.5 and 1.5 seconds of perception/reaction time respectively. Some values are omitted from these tables because they may be impractical or unachievable due to the steep grades. In those instances, designers should recognize that bicyclists may be traveling faster or slower than the typical design speed and adjust their design assumptions accordingly.

Table 3-4: Minimum Stopping Sight Distance vs. Grades for Various Design Speeds—2.5 Second Reaction Time

Table 3-5: Minimum Stopping Sight Distance vs Grade for Various Design Speeds—1.5 Second Reaction Time

3.5.2. Intersection Sight Distance

L&D Manual Volume 1, Section 201 establishes a range of recommended sight triangles that correspond to requirements for motorists to have sufficient space to identify, react, and potentially yield to other traffic at an intersection based on the traffic control applied at the intersection. Applying the sight triangle requirements provided in L&D Manual Volume 1, Section 201 will result in sufficient sight distance for some bicycle facilities, such as shared lanes and conventional bike lanes. Designers should consider the placement of bicyclists (often closer to the edge of the road in a shared lane environment or in a conventional bike lane) and their design speed when determining the sight triangles for these types of bicycle facilities.

Bike Case A: Right-Turning Motorist Across Separated Bike Lane or Side Path

Figure 3-3 depicts Bike Case A, which applies when a motorist is making a right turn across a separated bike lane or side path and bicyclists have concurrent through movement. 

In this case the motorist will be decelerating for the right turn approaching the intersection. The motorist’s turning speed is controlled by the intersection corner geometry and width of the receiving roadway. Table 3-6 identifies the minimum approach clear space, measured from the point of curvature of the motorist’s effective turning radius, which represents the location where the motorist will have decelerated to the turning speed; this location may or may not be the curb line point of curvature.

Clear space provides the necessary sight lines between motorists and bicyclists to yield (or stop) as appropriate. For locations with two-way separated bike lanes or side paths, additional approach clear space is not typically required, as the recognition zone between the counterflow bicyclist movement and the right-turning motorists should exceed the recommended sight distances. Approach clear space may be increased to account for steeper slopes or higher speeds for bicyclists.

Table 3-6: Intersection Approach Clear Space by Vehicular Turning Design Speed

*most low volume driveways and alleys

Bike Case B: Left-Turning Motorist Across Separated Bike Lane or Side Path

This case applies when a motorist is making a permissive left turn at a traffic signal or from an uncontrolled approach (e.g., a left turn from an arterial onto a local street or driveway). On one- way streets with a left-side separated bike lane or side path, this case has the same operational dynamics and approach clear space requirements as Bike Case A since the left-turning motorist will be turning adjacent to the separated bike lane. On two-way streets with a left-side separated bike lane or side path, there are two sight lines that should be maintained. A left-turning motorist approaching a turn needs a line of sight to bicyclists approaching from the same direction (see Figure 3-4). Table 3-6 identifies the minimum approach clear space based on the effective turning radius for the left-turning motorist. The provision of Bike Case A for motorists making a right-turn across a two-way bikeway will already provide the necessary line of sight between a left-turning motorist and a bicyclist approaching from the opposite direction.

On streets with two-way traffic flow, the operational dynamic of a motorist looking for gaps in traffic creates unique challenges that cannot be resolved through improving sight distance. This is a challenging maneuver because the motorist is primarily looking for gaps in oncoming motor vehicle

traffic and is less likely to scan for bicyclists approaching from behind. Unlike for Bike Case A or Bike Case B on one-way streets where the motorist is decelerating towards the crossing, the motorist in this case will be accelerating towards the crossing once they perceive a gap in traffic. This creates a higher potential for conflicts on roads with the following:

• High traffic volumes and multiple lanes
• Higher operating speeds
• High left turn volumes

Where it is not feasible to eliminate high speed and high-volume conflicts through signalization, turn prohibitions, or other traffic control, it may be necessary to reevaluate whether a side path or two-way separated bike lane is appropriate at the location, or provide an adequate motorist yield zone that allows the motorist to complete the turn while still yielding to crossing pedestrians or bicyclists (see Section 6.5.2).

Figure 3-4: Intersection Sight Distance Bike Case B

Bike Case C: Motorist Crossing of a Separated Bike Lane or Side Path/ Shared Use Path

This case applies when a motorist crosses a separated bike lane or side path and is similar to the cases in the Guide for the Development of Bicycle Facilities where a motorist crosses a bike lane or a mid-block path. The bike lane case is expanded upon below, including near-side and far-side intersection scenarios.

Bike Case C1 – Near-Side Crossing

This case applies when a motorist crosses a near-side separated bike lane or side path before continuing straight or turning at an intersection.

The two potential design scenarios are as follows:

Scenario #1: Two-Stage Crossing

Table 3-7: Bike Case C Intersection Sight Distance

Scenario #2: Single Crossing

In this scenario, the motorist assesses both the bikeway conflicts and motor vehicle conflicts from one stopped location, then performs the turning movement when there is a sufficient gap in both the bikeway and motor vehicle traffic (see Figure 3-6). This scenario may be appropriate in locations where the motorist would otherwise block the bike facility for extended periods of time or where bicycle volumes or motorist volumes are anticipated to be high. The equation in Table (3-7) should be used to calculate the departure sight triangle between a passenger vehicle and the bikeway using a time gap (t_g) of 4 seconds for the motorist to clear the bikeway. This time gap uses an assumption that the vertex (decision point) of the departure sight triangle is 10 ft. from the edge of bikeway and the bikeway width is no wider than 14 ft. The vertex of the departure triangle between the motorist and the intersecting motorist travel lanes will remain the same, but designers will need to adjust the typical time gap for the appropriate sight distance from L&D Manual Volume 1, Section 201.3.2 to account for the longer distance that the motorist will traverse. As shown in Figure 3-6, the provision of the motorist intersection sight distance will often accommodate the sight distance along the bikeway.

Figure 3-5: Intersection Sight Distance Bike Case C1 – Two-Stage Crossing Scenario

Figure 3-6: Intersection Sight Distance: Bike Case C1 – Single Crossing Scenario

Bike Case C2 – Far-Side Crossing

This case applies when a motorist crosses a far-side separated bike lane or side path (see Figure 3-7).

Where both the motorist and bikeway approaches are stop-controlled, providing a line of sight between the stopped motorist and the stopped bikeway user is appropriate.

Where the motorist approach is stop-controlled and the bikeway crossing is uncontrolled, the intersection sight distance described in L&D Manual Volume 1, Section 201.3.2.3 should be used to calculate departure sight triangle between the motorist and the intersecting bikeway. The bikeway design speed should be used in the intersection sight distance triangle calculation. The bikeway width and street buffer width should be converted to equivalent lane widths to adjust the time gap (tg) for the crossing of the roadway and the bikeway. In constrained situations, at a minimum the stopping sight distance (for bicyclists) should be provided to allow a bicyclist to slow or stop if a vehicle encroaches into the bikeway.

Figure 3-7: Intersection Sight Distance Case C2

As with Bike Case B, this case creates a challenging dynamic that is often difficult to resolve by increasing the size of the sight triangle. In urban areas, it may be difficult to increase the sight triangle enough to provide the intersection sight distance to judge gaps that allow a motorist to cross all the travel lanes as well as the separated bike lane/side path on the opposite side of the road. As such, designers should consider the frequency of through movements at these types of intersections and provide either traffic control devices or adequate sight distance (i.e., minimum stopping sight distance) for bicyclists to see and react to a crossing vehicle and stop if necessary. It may be appropriate to restrict these through motorist movements where traffic control devices or sight distances are inadequate.

Case C3 – Mid-Block Shared Use Path Crossing of a Roadway

If either the roadway approach or the shared use path approach is yield-controlled, adequate sight lines should be provided for a traveler on the yield-controlled approach to slow, stop, and avoid a user on the other approach. The length of the roadway leg of the sight triangle is based on a bicyclist’s ability to reach and cross the roadway if they do not see a potential vehicle conflict and have just passed the point where they can execute a stop without entering the intersection (see Figure 3-8 and Table 3-8). See Section 3.5.1 for additional information on bicyclist stopping sight distance.

Figure 3-8: Mid-Block Shared Use Path Crossing Sight Triangle

Table 3-8: Roadway Sight Triangle Equation

Similar to the roadway approach, the length of the path leg of the sight triangle is based on a motorist’s ability to reach and cross the junction if they do not see a potentially conflicting path user approaching and they have passed the point where they can execute a stop without entering the intersection. The length of the sight triangle along the path leg of each approach is given in Table 3-9.

Table 3-9: Path Sight Triangle Equation

Table 3-10 provides minimum distances for the length of the path and roadway legs of the sight triangle for flat terrain with basic assumptions about the site conditions and vehicle characteristics. If the appropriate approach sight distances cannot be provided, a more restrictive control should be used.

A key consideration at mid-block crossings for shared use paths is the need to consider mutual yielding dynamics at crosswalks (see Section 3.5). Where the path is stop- or yield-controlled, the departure sight distance for the path should be based on the slowest user who will have exposure to crossing traffic. This is typically the pedestrian. Under certain conditions it may be desirable to use a slower walking speed that is appropriate for seniors and children to calculate departure sight distance for the path crossing. Regardless of intersection sight triangle lengths, roadway and path approaches to an intersection should provide sufficient stopping sight distance so that motorists and bicyclists can avoid obstacles or potential conflicts within the intersection.

Table 3-10: Length of Path and Roadway Sight Triangle (ft)

Assumptions:

Bicycle reaction time = 1.5 sec
Width of path = 10 ft to 11 ft
Width of road lane = 11 ft to 12 ft
Length of bicycle = 6 ft
Length of motor vehicle = 18 ft
Grade = -2% to 0%

Bike Case D – Bicyclist Crossing from a Minor Road

Where a stop-controlled roadway intersects an uncontrolled roadway, bicyclists must judge the speed of, and gaps in, approaching motor vehicle traffic from their location at the edge of the roadway (see Figure 3-9). Providing the minimum stopping sight distance for the motorist on the uncontrolled roadway approach will allow the motorist sufficient time to exercise due care to slow or stop for the crossing bicyclist who may still be in the intersection. Table 3-11 provides the length of the departure sight triangle along the roadway to allow the bicyclist enough time to judge a gap in traffic and complete a full crossing of the roadway without a motorist needing to slow or stop. The table assumes a bicyclist with a:

• design acceleration of 2.5 ft/s2,
• maximum speed of 8 mph to account for a slow bicyclist, and
• bicycle length of 6 ft.

Figure 3-9: Bicyclist Crossing from a Minor Road Case D

Table 3-11: Bicyclist Sight Distance Crossing from a Minor Road Case D

Bike Case E – Shared Use Path Crossing of another Shared Use Path

As shown in Figure 3-10, if a shared use path intersects another shared use path and the intersection is uncontrolled, sight triangles similar to the yield condition described in Bike Case C3 above should be provided. However, both legs of the sight triangle should be based on the stopping sight distances of the paths. Use the equation in Table 3-9 or value “b” from Table 3-10 for both legs of the sight triangle. If sufficient sight distance cannot be provided, traffic control, such as a stop sign or shared use path roundabout, must be considered.

Figure 3-10: Bicyclist Crossing a Shared Use Path from a Shared Use Path Case E

Bike Case F – Bikeway Crossings of Walkways

At an intersection of a stop-controlled shared use path and a walkway, a clear sight triangle extending at least 15 ft. along the walkway and 25 ft. along the shared use path should be provided to ensure clear lines of sight between the path and walkway users (see Figure 3-11).

Figure 3-11: Minimum Path-Walkway Sight Triangle

At an intersection of a walkway and an uncontrolled shared use path, or where a pedestrian crosses a separated bike lane (e.g., to cross a street, access a crossing island, or floating bus stop), the length of the clear sight triangle along the bikeway should be determined using the equation presented in Table 3-12 or the minimum stopping sight distance (see Table 3-3), whichever is smaller. The length of the sight triangle along the intersecting walkway should be determined using the equation presented in Table 3-12 or if a curb ramp is present the length should be the distance between the curb line and the pedestrian landing at the top of the curb ramp (see Figure 3-12). The clear sight triangle provides sufficient time for pedestrians walking (3.5 ft/s) or running (12.5 ft/s) to judge gaps in approaching bicycle traffic and for bicyclists to perceive the presence of a pedestrian and slow or stop as necessary. If pedestrian crossings of bikeways is unexpected, signs may also be provided to warn bicyclists of the pedestrian crossing.

Table 3-12: Pedestrian and Bicyclist Intersection Sight Distance

* If a curb ramp is present for the walkway, the length of a should be the distance between the curb line and the level landing at the top of the curb ramp.

Figure 3-12: Pedestrian Crossing Shared Use Path or Separated Bikeway (shown) Sight Triangle

3.6 Geometric Design Elements

Key controls in geometric design for bicycle and pedestrian facilities are directly related to the characteristics of the various users of the facilities and the characteristics of motor vehicles where the facilities interface with roadways. The L&D and other adopted policies adequately covers the characteristics of motor vehicles and that information is not repeated here. However, in some cases relevant motor vehicle characteristics from the AASHTO “Green Book” are noted or are used in developing bicycle and pedestrian facility geometric design guidance.

As discussed in Section 3.6.1, the physical dimensions and operating characteristics of people walking and bicycling vary considerably. By choosing geometric design values that fit the upright adult bicyclist, most other users of the bicycle facility will be accommodated. For example, a railing designed to protect an adult bicyclist will protect a shorter child bicyclist. Providing designs that serve the operating space of the adult bicyclist will accommodate the most common design user operating in bicycle facilities, except for some vehicles and equestrians that may use shared use paths (see Chapter 6).

3.6.1. User Operating Space and Facility Widths

In addition to establishing the user profile and performance characteristics of people walking and bicycling, designers should understand the principles of operating space. When developing design parameters for sidewalk and bikeway widths, designers should consider the space occupied by the user and whatever device they may have, their operating space, and any additional shy space to vertical objects or obstructions adjacent to them (See Section 3.6.2). These combined operating and shy spaces are used to establish width requirements for sidewalk facilities, bicycle facilities, and shared use paths as discussed in Chapters 4, 5, and 6.

Physical Space

The figures in Section 3.2.2 shows that there are multiple types of bicycles and other devices for consideration. Though Section 3.2.1 notes that there is not a single design pedestrian, for the purpose of defining typical physical space dimensions, a typical adult in a wheelchair should be assumed for pedestrians:

• 3 ft. width
• 4 ft. length

When facilities include bicyclists, it is recommended that the design user be an adult bicyclist with a trailer in order to accommodate most users. The following minimum physical space dimensions should be used:

• 2.5 ft. width
• 10 ft. length
• 7 ft. height

Operating Space

The lateral operating space extends beyond the physical space to allow pedestrians and bicyclists the natural side-to-side movement that varies with speed, topography, traffic conditions, wind, and proficiency.

The operating space of a person walking varies based on the purpose of the trip and the space available in front of them. In general, it is assumed that a person in a wheelchair or using crutches can operate within a width of 3 ft.

For pedestrians with mobility devices, spatial needs will vary. Figure 3-138 below illustrates the increased space that may be required to accommodate the movements of pedestrians with mobility devices.

To accommodate the side-to-side movement of almost all bicyclists, the minimum effective operating space clear of all obstructions for a bicyclist should therefore be 3.5 ft., which accounts for a 30 inch physical width and 6 inches of space on either side (see Figure 3-14). This operating space should provide a smooth, rideable surface clear of surface defects, joints, and other potential obstructions including drainage grates. Where it is desired to accommodate larger bicycles or larger variations in straight-line travel, the operating width should be increased. Additional discussion of conditions where shy space should be considered is provided in Section 3.6.2.

Figure 3-13: Spatial Dimensions for People Using Typical Mobility Devices

The operating space must also consider vertical clearances to obstructions such as trees, signs, utilities, ceilings and other potential hazards. Fixed objects should not be permitted to protrude within the vertical operating space of a bicycle or pedestrian facility. The recommended minimum vertical operating space that may be used is 8 ft. The preferable vertical operating and shy space is 10 ft.

Figure 3-14: Typical Adult Bicyclist Operating Space

3.6.2. Shy Spaces

To maintain comfort and safety of pedestrians and bicyclists, it is important to consider providing clearances to obstructions adjacent to sidewalks and bikeways. For example, a contributing factor in many bicycle crashes is a bicyclist striking another person or object with their handlebar or wheel. Clearances to vertical elements should be provided as shy spaces located outside the operating space of the bicyclist. However, for bikeways within the roadway, it may not always be practicable to provide shy space to parked and moving motor vehicles just as sidewalks are sometimes placed directly adjacent to the curb and moving vehicles. Where minimum shy spaces are not provided, the useable width intended for bicycle travel and pedestrian movement, and the level of comfort for the facility, is likely to be reduced.

This section provides guidance for determining an appropriate clearance distance to obstructions and on the relevance of shy space for common contexts. See Table 3-13 for bicyclist shy spaces to common vertical elements.

Table 3-13: Bicyclist Shy Spaces

Bicycle Traffic

People walking or bicycling have the potential to collide into other bicyclists or pedestrians (on shared use paths) where a facility width limits a users’ ability to operate side-by-side, to pass other users of the same mode, or to pass other modes. Sidewalks and bikeways should be constructed to serve the expected volume of users to minimize this crash risk. A minimum shy space of 12 inches should be included to accommodate passing or side-by-side bicycling, though this may be reduced to 6 inches in constrained conditions. Where it is desired to accommodate side-by-side bicycling or frequent passing, shy space should be provided between the operating spaces of each user. Where it is not desired to encourage side-by-side bicycling, shy space should still be provided between the physical spaces of each bicyclist to accommodate occasional passing. Figure 3-15 depicts shy space from both physical and operating spaces for side-by-side bicycling and occasional passing scenarios.

Figure 3-15: Bicyclist Shy Space to Vertical Elements Accommodating Side-By-Side Bicycling and Occasional Passing

Intermittent Vertical Elements

Intermittent vertical elements along the edge of a bicyclists’ path, such as trees, signs, utility poles, flexible delineator posts, or other similar objects, can increase the risk of handlebar strikes or bicycle trailers striking vertical elements. Similarly, pedestrians will position themselves away from these obstructions to avoid hitting them with their arm or belongings. Where these features are present, the minimum shy space is 1ft., although the shy space may be eliminated in constrained areas. Exceptions to this guidance are as follows:

• The OMUTCD requires no portion of a sign or its support to be placed less than 2 ft. laterally from the near edge of a shared use path. Where space is available, wider shy spaces are desirable.
• Bicycle-only pushbuttons or pushbuttons on shared use paths should be located close enough to be pressed without dismounting and placed based on pedestrian accessibility guidelines. The OMUTCD and Chapter 8 provide additional guidance on the location of pushbuttons.
• Lean rails and footrests intended for the use of bicyclists at intersections are an exception to the shy distance guidelines and should be located close enough to be functional from the bikeway. Bikeways may be widened to provide shy distances and allow these treatments to be functional.

Continuous Vertical Elements

Continuous vertical elements, such as fences, railings, barriers, and walls, can also increase the risk of handlebar and bicycle trailer strikes. In this case, the constant presence of these elements will result in pedestrians and bicyclists attempting to increase their separation from them as these elements create a feeling of enclosure. Where these features are present, a minimum buffer width is 2 ft., but may be reduced to 1 ft. in constrained locations. Where space is available, wider buffers are desirable. Designers may use warning signs, object markers, or enhanced conspicuity and reflectorizing of the obstruction to draw attention to their presence.

Curb and Gutter

Some curb types can increase the risk of bicycle crashes if struck by a wheel or pedal. The face of curb angle—vertical, sloping, and mountable—and curb height influence the functional width of the bikeway, crash risk to bicyclists, the ability to exit bikeways, and the risk of encroachment into the bikeway by other users. In locations where the bikeway is located between curb on one or both sides, it is preferable to provide sloping curbs or reduced height vertical curbs (less than 3 inches). The following shy distances should be used for the different curb types:

• Where vertical curbs are provided, the minimum shy space is 6 inches and the preferable shy space is 1 ft.
• Where sloping curbs are provided, there is no minimum shy space adjacent to the curb; however, shy space behind the curb to other appurtenances is still relevant.
• Where mountable curbs are provided, there is no minimum shy space adjacent to the curb; however, shy space to other appurtenances should be carefully considered along the bicyclists expected path of travel if they are permitted to exit the bikeway (such as to access bicycle parking).
• Where curb with integral gutter creates a longitudinal joint parallel to the bikeway, the gutter area is not included in the width of the bikeway but there is no minimum shy space from the edge of gutter.

Some curbs are constructed with integral gutters that include a longitudinal seam parallel to bicycle travel that may deteriorate, resulting in dips or ridges that increase crash risk for bicyclists. Gutters also may have uneven surfaces where street resurfacing activities do not adequately remove asphalt approaching the gutter. Where curbs are provided with integral gutter, the minimum shy space from the bicyclist to the curb is the width of the gutter. See Chapters 4 and 6 for additional information relating to curb selection and design.

Some curb heights may warrant a railing when introduced within a walking area that is separating a lower portion of sidewalk from an upper portion of sidewalk. A railing should be installed when that curb height is greater than 6 inches and consideration should be given to including one when the curb height is at 6 inches. The railing serves as protection and support for pedestrians with vision impairments.

Vertical Clearance

The preferred vertical clearance to overhead obstructions is a minimum of 10 ft. for sidewalks, shared use paths, and bikeways. If any portion of a pedestrian facility has a clearance less than 80 inches., it shall be shielded by a barrier which is detectable with a cane at an elevation no higher than 27 inches.⁹ The minimum vertical clearance that may be used in constrained areas is 8 ft. In some situations, vertical clearance greater than 10 ft. may be needed to permit passage of maintenance and emergency vehicles or where equestrian use may be expected. Providing additional vertical clearances can also improve the comfort of a facility in an otherwise constrained location (e.g., a relatively long underpass). Vertical clearance should be considered for underpasses and tunnels, as well as for overhead signs, trees, and other appurtenances that may extend over a bicycle or pedestrian facility.

3.6.3. Horizontal Alignment

Basic horizontal geometric design guidelines for motor vehicles will typically result in a facility that accommodates bicyclist and pedestrians. Guidelines for the horizontal alignment of shared use paths that deviate from a roadway alignment will be discussed in more detail in Chapter 5 as a part of the shared use path design principles.

Sidewalks

While the horizontal alignment for sidewalks typically follows the roadway, designers may have a situation where the sidewalk is independent of a roadway and in these situations, care should be given to providing consistent design elements. For pedestrians with vision impairments or using mobility devices, sidewalks with straight alignments are preferred for ease of navigation. If any curvature is introduced, it should be gradual and sweeping, with forgiving infrastructure adjacent to the walk, preventing pedestrians with vision impairments from wandering off of the sidewalk because the edge is difficult to detect, and minimize maneuvers for pedestrians with mobility devices.

Bicycle Tapers

Changing the horizontal alignment of a bikeway may be accomplished without the use of horizontal curves if shifting tapers are used. Tapers should generally occur gradually, with a minimum length as calculated using the formula in Table 3-14. If the bikeway is delineated by paint- only, and if the off-tracking of a bicycle pulling a trailer would not put the trailer into a motor vehicle lane, a maximum taper ratio of 2:1 (longitudinal:lateral) may be considered. See Figure 3-16.

Table 3-14: Shifting Taper Equation

Figure 3-16: Bikeway Shifting Tapers

3.6.4. Cross Slope

For all facilities that include pedestrians, cross slope design should meet pedestrian accessibility guidelines and shall be a maximum of 1.56 percent to comply with ADA guidance. Cross slopes of 1 percent are more comfortable for people with disabilities and people bicycling with more than two wheels (e.g., cargo bike, adult tricycles, or trailers). In cases where the facility is designed for bicycle use only (e.g., pedestrians are accommodated on a separate walkway), cross slopes may exceed pedestrian accessibility guidelines.

3.6.5. Vertical Alignment

For facilities shared by bicyclists and pedestrians and for pedestrian only facilities, longitudinal grades should meet pedestrian accessibility guidelines. A sidewalk or bikeway adjacent and parallel to a roadway should generally match the grade of the adjacent roadway. Where a bikeway runs parallel to a roadway with a grade that exceeds 5 percent, the bikeway grade may exceed 5 percent but should be less than or equal to the roadway grade.

3.7 Other Considerations

3.7.1. Utilities

It is common to locate utilities within roadway corridors and to take advantage of utility rights-of- way to construct trails and shared use paths. This often creates challenges related to placement of utilities in relation to bicycle facilities.

Addressing utility location may not be practical in retrofit situations where minimal reconstruction is anticipated. However, new construction or substantial reconstruction presents opportunities to proactively address utility placement. Careful consideration of utilities within a roadway corridor can minimize potential utility conflicts and ensure adequate maintenance access for both utilities and bicycle facilities. Utility placement should be coordinated early in the project with utility owners and as part of the drainage and signal design. The following list represents common utility issues that may be encountered when designing bicycle facilities.

Adjacent Utility Features

The usable width of bikeways and sidewalks is reduced if a utility feature such as a pole or fire hydrant is located immediately adjacent to a bikeway. See Section 3.6.2 for information on shy distances to obstructions. It is preferable to locate fire hydrants in the buffer adjacent to a sidewalk or bikeway. Designers should coordinate with the local water department to determine exact hydrant placement. Additionally, the placement of valves, pull boxes, manhole lids, and grates could impact the design of curb ramps at pedestrian crossing locations.

Guy wires for overhead pole lines can create a vertical obstruction for pedestrians and bicyclists. The angle of the guy wire within the bicycle and pedestrian facility will require analysis to ensure the wire doesn’t extend into the vertical clear zone and create the risk of a pedestrian or bicyclists running into the wire.

Pad mounted transformers, telecommunication cabinets, and other cabinets for surface utilities can cause obstructions in the pedestrian access route or bicycle path. When designing pedestrian and bicycle facilities, coordinate existing infrastructure with the utility owner and facility design to provide the minimum accessibility width. If relocating these facilities, it is recommended these facilities be placed behind the sidewalk or bikeway as right-of-way permits to avoid vertical obstructions that could cause potential sight distance issues for the bicyclists or pedestrian and motorists.

Underground Utilities

Avoid locating utility covers and large ventilation grates within bikeways to maintain a level bicycling surface and minimize detours during utility work. Where unavoidable, utility covers and large ventilation grates within bikeways should be smooth and flush with the bikeway surface and placed in a manner that minimizes the need for avoidance maneuvers by bicyclists. In addition, keeping manholes flush within one-quarter inch below the pavement surface helps to avoid impacts to winter maintenance equipment. When utility cuts are necessary within a bikeway, the repaired pavement should extend the entire width of the bike lane to prevent uneven riding surfaces.

Due to their typically large size, ventilation grates may present a skidding hazard if located in a bikeway. If placement in a bikeway is unavoidable, designers should consider skid resistant treatments.

For pedestrian facilities, utility covers and grates must meet gap requirements for openings and surface treatment requirements for accessibility guidelines, i.e., ¼-inch maximum. If these elements are not accessible, the grate or cover can impact the accessible width of the pedestrian facility.

Traffic Signal Equipment

The addition of bikeways within the footprint of an existing roadway often results in the need to realign traffic signal heads and detection equipment. Designers shall consider configuration of traffic signal and detection equipment in relationship to alignment of travel lanes to determine whether traffic signal modifications are necessary. Additionally, the placement of signal cabinets should be considered when assessing sight lines to ensure that the equipment will not result in sight obstructions. See Chapter 8 for a discussion of bicycle signals and placement of pushbuttons.

Some pedestrian signal equipment is required to meet ADA requirements and is discussed in Chapter 4. Other pedestrian signal elements can include rapid rectangular flashing beacons and pedestrian hybrid beacons. For design information related to these elements, see Chapter 8, OMUTCD Parts 4 and 9, and TEM Parts 4 and 9.

3.7.2. Lighting

A properly lit area creates a comfortable and functional environment for all street users. A well-lit street provides drivers with more opportunity to see the bicyclists or pedestrians in the roadway and to stop or maneuver to avoid them. For both pedestrians and bicyclists, lighting directly impacts real and perceived safety, influencing one’s decision and willingness to walk or bike in an area.

For sidewalks, bikeways, and shared use paths, fixed-source lighting improves visibility along the path of travel, allowing users to better detect surface irregularities at night. Provision of lighting appropriate for all users should be considered, especially when night-time use is anticipated, such as the following locations:

• On pedestrian and bicycle facilities that provide connections to transit stops and stations, schools, universities, shopping, and employment areas,
• Under vehicular bridges, underpasses, tunnels, or locations with limited visibility,
• Along bridges used by bicycles and pedestrians,
• Along high-use portions of facilities that lead to areas with frequent evening events,
• At intersections or driveways where crossing are required, and
• At major shared use path intersections and entrances.

Along pedestrian and bicycle facilities, pedestrian-scale lighting is preferred to tall, highway-style lamps. Pedestrian-scale lighting is characterized by shorter light poles (approx. 15 ft. high), lower levels of illumination (except at crossings), closer spacing (to avoid dark zones between luminaires), and light emitting diode (LED) lamps. This approach to lighting design can improve lighting uniformity along the walkway or bikeway and at conflict points, helping to address issues of social safety and bicycle and pedestrian visibility. Streetlights should comply with local streetscape or historic district guidelines to enhance placemaking and work in the local context.

Depending on the location, average maintained horizontal illumination levels of 0.5- to 2-ft candles should be considered, and lighting levels should provide a uniform illumination of the walkway and bikeway surface. Higher lighting levels may be appropriate in some locations to increase the perception of personal safety.

Placement of light poles should provide the recommended horizontal and vertical clearances from the walkway and bikeway. Where pedestrians cross bikeways, or where bicyclists or pedestrians cross motor vehicle paths, the lighting placements should front light (illuminate) the crossing user to make them more visible to the approaching bicyclist or motorist.

Light fixtures should be chosen to reduce the loss of light and may need to comply with local “dark sky” guidelines and regulations. Lighting in natural and undeveloped areas may ultimately be undesirable to mitigate environmental disturbance, or may be designed to dim or turn off lighting after curfew along riparian corridors and other less/undeveloped areas.

Additional guidance for lighting can be found in the AASHTO Roadway Lighting Design Guide and the TEM Section 1100.

3.7.3. Drainage

Ensure drainage is provided on bike and pedestrian facilities to prevent water ponding, ice formation, and the collection of debris. Refer to L&D, Volume 2 for the design Annual Exceedance Probability event storm for bicycle pathways. Proper drainage protects the longevity of the infrastructure, reduces erosion, and follows local and state guidance for stormwater runoff collection. The minimum recommended hard surface cross slope of 1 percent typically provides adequate conveyance of drainage. For sidewalks or bikeways, sloping in one direction instead of crowning is preferred and simplifies drainage and surface construction.

Bikeways along or within a road corridor typically follow the slope and drainage patterns of the respective roadway, and may be incorporated into the roadway’s drainage system. If the bikeway changes drainage patterns or adds impervious area to the design, the roadway’s drainage system will likely need to be modified or expanded.

Utility covers and bicycle compatible grates should be flush with the surface of the pavement on all sides. Any horizontal openings shall not permit passage of a sphere more than 0.5 inches in diameter. Additionally, the gap between the frame and catch basin grate shall not exceed 0.5 inches. Inlet Grate from ODOT Standard Construction Drawing CB-6 shall be used whenever bike traffic is expected. Any elongated openings shall be placed so that the long dimension is perpendicular to the direction of travel.

Pedestrian accessibility guidelines also limit vertical deviations in surfaces of more than 0.25 inches. To minimize risks to pedestrians, drainage grates, utility covers, and gutters should not be located within bicycle facilities where pedestrians are traveling unless they meet pedestrian accessibility guidelines.

Any infrastructure located in low-lying areas may need special attention to larger scale drainage and flooding issues. Designers may need to capture excess stormwater to prevent standing water or erosion on a pedestrian or bicycle facility.

For pedestrian facilities, positive drainage at the base of curb ramps is critical to prevent debris from gathering or water from ponding during rain events or freezing in cold weather. Placing a catch basin or inlet immediately upstream from a curb ramp will capture a majority of storm runoff prior to the water passing the curb ramp base, minimizing the amount of water flowing past the ramp area. Minimum sidewalk cross slopes should be maintained to promote positive drainage away from the sidewalk area. Ideally, where curb or curb and gutter exist, sidewalks will slope to the roadway, directing water over the curb to the gutter and into a storm sewer system. Where a swale is placed between the roadway and the sidewalk, or at the back of sidewalk and water is directed into the swale, the swale design shall follow L&D Manual Volume 2 and ensure adequate freeboard is provided to prevent water from overtopping the swale and ponding on the sidewalk.

3.7.4. Landscaping

Landscaping should follow the guidance in L&D Manual Volume 1, Sections 600 and 900, and the ODOT Aesthetic Design Guidelines. Landscaping must be designed to allow sufficient sight distance, and proper offsets should also be provided from roadways to comply with clear zone and urban arterial offsets.

Well-designed landscaping—trees, shrubs and grasses—alongside sidewalks and bike facilities creates a more pleasant walking and bicycling environment, improves community aesthetics, and can help to reduce motorist speeds by visually narrowing the roadway. Landscaping, including defining maintenance roles, should be coordinated during preliminary design stages.

Street trees are the primary consideration for landscape design along sidewalks and separated bike lanes. With respect to the separated bike lane cross-section, trees may be located in the street buffer, in sidewalk buffers, or both. The street buffer is the recommended tree planting location to preserve usable sidewalk width and enhance the separation between motor vehicles and bicyclists in constrained corridors, but the sidewalk buffer may be considered to provide shade for the sidewalk or where the street buffer is too narrow.

When selecting tree species, ensure compatibility with the bicyclist operating height (100 inches vertical clearance from bike lane surface to tree branches). Avoid shallow rooted species and species that produce an abundance of fruits, nuts, and leaf litter. Properly designed tree trenches, tree pits, or raised tree beds can support root growth to preserve pavement quality of the adjacent separated bike lane. Coordinate street tree species selection with overhead utility owners to identify a tree that will not require extensive trimming to avoid interference with the utility lines as it matures. This will preserve the future tree canopy, increasing the shade and aesthetics of the bicycle and pedestrian facilities.

Where on-street parking is present, intermittent curb extensions with street trees between parking spaces can preserve sidewalk space and visually narrow the roadway for a traffic calming effect.

Tree plantings can also be integrated with stormwater management techniques.

The design of separated bike lanes and side paths in rural and low-density suburban communities should follow natural roadside design considerations. Natural roadside corridors are bound by the limits of the available right-of-way and should be designed accordingly. Motor vehicle speeds in these corridors are typically higher than in urban environments, therefore it is important to maximize the street buffer to the extent possible to provide greater separation from high-speed motor vehicle traffic. Methods to achieve this may include:

• fitting the separated bike lane or shared use path to the natural terrain, but maintaining grades that are comfortable for bicycling and meet ADA requirements if pedestrians are present;
• avoiding and minimizing impacts to wetland resources or other natural environments;
• where possible, maintaining natural drainage patterns and minimizing erosion through the use of vegetated drainage channels in the street buffer; or
• maintaining access for periodic mowing and other maintenance activities.

3.7.5. Surface Conditions

It is important to construct and maintain a smooth traversable surface on pedestrian and bicycle transportation facilities. Wheelchairs, electric mobility scooters, bicycles, and other wheeled users require firm, stable surfaces and structures (eg. ramps, beveled edges) since they can be difficult to propel over uneven surfaces. Hard, all-weather pavement surfaces are recommended for pedestrian and bicycle facilities. For on-street and separated bike lanes, concrete or asphalt pavement is typically appropriate.

Shared use paths must meet pedestrian accessibility surface requirements. All-weather pavement is preferred compared with crushed aggregate, sand, clay, or stabilized earth. Since unpaved surfaces provide less traction, they decrease braking ability for bicyclists which can cause bicyclists to more easily lose control. On unpaved surfaces, bicyclists and other wheeled users must use a greater effort to travel at a given speed when compared to a paved surface. Some path users, such as skaters, are unable to use unpaved paths. In areas that experience frequent or even occasional flooding or drainage problems, or in areas of moderate or steep terrain, unpaved surfaces will often erode and require substantial maintenance. Additionally, unpaved paths are difficult to plow for use during the winter.

On shared use paths, loads should be substantially less than roadways. However, paths should be designed to sustain wheel loads of occasional emergency, patrol, maintenance, and other motor vehicles that are permitted to use or cross the path. When motor vehicles are driven on shared use paths, their wheels often will be at, or very near, the edges of the path. This can cause edge damage that, in turn, will reduce the effective operating width of the path. The path should, therefore, be constructed of sufficient width to accommodate the vehicles, and adequate edge support should be provided. Edge support can be provided by means of stabilized shoulders, flush or raised concrete curbing, or additional pavement width or thickness. The use of flush concrete curbing has other long-term maintenance benefits, such as reducing the potential for encroachment of vegetation onto the path surface. If raised curbs are used, refer to Section 3.6.2 for shy distance and curb design considerations.

Rumble strips and stripes are tactile patterns constructed along the edge of a travel lane or paved shoulder or along the road center line. They are typically milled into existing pavement, but sometimes they are created by adhering raised devices to the pavement.¹⁰ The texture of rumble strips is different from that of the roadway surface, and is designed to give motorists an audible and tactile cue to correct their course when a motorist drives over them. Longitudinal rumble strips and stripes that are milled into the roadway surface have proven to be an effective and inexpensive way to reduce run-off-road crashes for motorists on high-speed roadways.¹¹ However, they can be difficult for bicyclists to traverse and can render popular and useful bicycle routes or shoulders unusable by bicyclists. The effect of some rumble strip designs on bicyclists can be significant if not properly mitigated, causing the bicycle to shudder violently and/or the bicyclist to lose control. Additional details on the design and placement of rumble strips and stripes is discussed in Chapter 6.

Railroad tracks that interface with pedestrian and bicycle facilities can be hazardous to wheelchair users, mobility impaired, and bicyclists. See Chapter 11 for railroad crossing considerations.

Chapter 3 Endnotes

1. FHWA. Bicycle and Pedestrian Facility Design Flexibility. Memorandum. HEPH-10. Federal Highway Administration, U.S. Department of Transportation, Washington DC, 2013.
2. Jacobsen, P. L. Safety in Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling. Injury Prevention, Vol. 9, No. 3, 2003, pp. 205–209.
3. Elvik, R. The Non-Linearity of Risk and the Promotion of Environmentally Sustainable Transport. Accident Analysis and Prevention, Vol., 41, No. 4, 2009, pp. 849–855.
4. Marques, R. and V. Hernandez-Herrador. On the Effect of Networks of Cycle-Tracks on the Risk of Cycling: The Case of Seville. Accident Analysis and Prevention, Vol. 102, 2017, pp. 181-190.
5. http://www.fhwa.dot.gov/environment/bicycle_pedestrian/publications/net  work_report/network_report.pdf
6. Dill, D. and N. McNeil. Revisiting the Four Types of Cyclists. In Transportation Research Record 2587. TRB, National Research Council, Washington, DC, 2016.
7. https://www.fhwa.dot.gov/publications/research/safety/pedbike/05085/chapt8.cfm
8. https://www.fhwa.dot.gov/publications/research/safety/pedbike/05085/pdf/lesson8lo.pdf
9. U.S. Access Board. Proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way. 36 CFR, Part 1190, 76 Federal Register 44664, published July 26, 2011. United States Access Board, Washington, DC, 2011. http://www.access-board.gov/guide-lines-and-standards/streets-sidewalks/public-rights-of-way/proposed-rights-of-way-guidelines.
10. AASHTO. A Policy on Geometric Design of Highways and Streets. American Association of State Highway and Transportation Officials, Washington, DC, 2011.
11. Torbic, D. J., J. M. Hutton, C. D. Bokenkroger, K. M. Bauer, D. W. Harwood, D. K. Gilmore, S. M. Dunn, J. J. Ronchetto, E. T. Donnell, H. J. Sommer III, P. Garvey, B. Persaud, and C. Lyon. National Cooperative Highway