Published: April 21, 2021

Conduit Inventory

This guide is intended for use by ODOT Districts in coding culvert and storm drain information. The Conduit Management Manual (CMM) is recommended for other agencies, Counties, Municipalities, Turnpike Commission, etc., as an outline for their own internal use.

The primary intent of the inventory and inspection guidelines outlined in the CMM is to ensure the safety of the motoring public. The required inventory items outlined below were determined with this goal in mind. Conduit location and size are the primary factors considered when determining inventory item guidelines.

Required Inventory Items:

• ODOT will maintain an inventory of culverts with a span or diameter of 12 inches or greater but less than 120 inches that are located under pavements and paved shoulders, Type A Conduits, and are owned or maintained by the Department.
• ODOT will maintain an inventory of storm drains with a span or diameter of 12 inches or greater but less than 120 inches that are located under pavements, Type B Conduits, and are owned or maintained by the Department.
• Longitudinal storm drains located under traveled lanes will also be included in the inventory.
• Longitudinal storm drains located under the paved shoulders will only be included if a defect in the storm drain will have a direct impact on the traveled lanes.

Periodic inspections will take place on all conduits meeting the above criteria. Frequency of these inspections is per section III Conduit Inspection, 8. Frequency of Inspection. Statewide funding decisions determining District allocations for conduit rehabilitation and replacement will be based from the required inventory items.

No conduit less than 12 inches in span or diameter will be included in the conduit inventory.

Inspectors are to keep in mind that any conduit with a span of 10 feet or greater when measured parallel to the centerline of the roadway is to be placed on the Bridge Inventory and inspected according to the ODOT Manual of Bridge Inspection: Reference Item 18. Span and Item 26. Skew for further guidance. Any bridge found to have been erroneously placed on the Conduit Inventory is to be removed. Prior to removal, verify that the conduit is on the Bridge Inventory, if not, the information should be transferred for placement on the Bridge Inventory.

Updating the inventory consists of adding conduits, retiring conduits, editing the existing inventory or adding modifications and creating proposed conduits. When a conduit undergoes a complete removal and replacement with a new conduit, the removed Conduit File Number (CFN) will be retired from the active conduit database. A new Conduit File Number will be assigned to the new conduit when you create a new inventory with the Collector App. Note that this new inventory data will need to be uploaded followed by an automated overnight script process before you will see the CFN in the data. The Districts are responsible for inventory changes and performance of inspections. Suggested changes to the manual should be directed to the OHE.

A Conduit Inventory form (CR87) is shown in the Appendix B.

Inventory and Inspection Notes and Special Conditions

While culverts and storm drains serve a similar function, they vary greatly regarding their design methodology and flow characteristics. For our purposes at ODOT, culverts and storm drains may be differentiated based upon their inlet end condition. Conduits with closed end inlet conditions, catch basin, inlet, manhole. etc., are considered storm drains, while conduits with open ended inlets are classified as culverts.

Unique Conditions:

In cases where multi-cell conduits are treated as one conduit, reference Item 18. Span, some judgment will be required on the part of the inspector when coding the conduit inventory and Inspection forms. In cases where material properties differ between cells, the conduit with the largest individual span is to be used to populate the Inventory Report. When performing an inspection on a multi-cell conduit, the worst individual conditions found at the site are to be used to populate the individual ratings. Keep in mind that the material under the roadway takes precedence. Example: The conduit with the worst alignment would determine the conduit Alignment rating; the worst headwall condition would determine the Headwall rating, etc.

Sometimes an individual culvert or storm drain may have multiple sizes, material types, shapes or all under a single CFN. OHE recommends that a new CFN should be assigned to each section that changes in size, material type, shape or all. This could ultimately lead to the creation of numerous CFN’s so it will be left to the discretion of the District. Keep in mind that the material under the roadway takes precedence. The inspector should expect to encounter unique situations in the field where conditions may vary from the typical situations outlined in the Manual and on the Inventory and Inspection forms.

Safety:

Due to their stable nature, culverts generally do not contain physical threats such as the potential to trap or engulf an entrant. Conduits that are fully or partially collapsed or have significant infiltration of backfill material or water pose an additional physical threat and should not be entered.

Inspection procedures will vary regarding the safety measures used. There are several factors that determine the applicable safety procedures: Conduit size, conduit length, the ability to see the opposite end, and conduit history.

Note: The Conduit inspector must complete the Conduit Inventory and Inspection Class prior to preforming an Inventory or Inspection of a conduit. These qualifications are listed within Section III Conduit Inspection of this manual. Only a Bridge Engineer is exempt from needing to take the Conduit Inventory and Inspection Class.

1. Coding the Conduit Inventory on Collector App. or CR-87 Form

Code the inventory fields according to the individual instructions below. Please leave any unknown fields blank. For each item, R = Required to collect, O = Optional to collect, C = Calculated automatically based on its latitude and longitude (GPS) or a formula.

Conduit File Number

The Conduit File Number (CFN) is a unique 7-digit number that identifies the conduit. When a conduit is initially inventoried, the Conduit Collector Application assigns a unique CFN to the conduit. The Conduit Web Application can also be used to create a unique CFN.

When an existing conduit is replaced or when installing a new conduit where one did not previously exist, a new CFN is to be assigned to the new conduit and the conduit being replaced is retired through the Conduit Collector Application or the Conduit Web Application. A nightly process to the Statewide Conduit Database will populate inventory data related to the NLF ID and ensure the most accurate straight-line mileage.

NOTE: Districts choosing to install conduit marking signs are to refer to:

Sign Designs and Markings Manual (SDMM)
Standard Sign Design - ODOT - Office of Traffic Operations
Code No. I-H25b

2. Location & Route Information

C - Item 1. District

This field will be generated after the field coordinates of the conduit have been collected via GPS. Refer to Item 6 Note.

C - Item 2. County

This field will be generated after the field coordinates of the conduit have been collected via GPS. Refer to Item 6 Note.

C - Item 3. Route

This field will be generated after the field coordinates of the conduit have been collected via GPS. Refer to Item 6 Note.

C - Item 4. Straight Line Mileage

This field will be generated after the field coordinates of the conduit have been collected via GPS using the most current linear references. Refer to Item 6 Note.

C - Item 5. Latitude

This field will be generated after the field coordinates of the conduit have been collected via GPS. Refer to Item 6 Note.

Ohio Limits are from 38.400000 degrees to 41.980000 degrees.

C - Item 6. Longitude

This field will be generated after the field coordinates of the conduit have been collected via GPS.
Ohio Limits are from -84.816666 degrees to -80.516666 degrees.

Note: The latitude and longitude should be collected where the conduit crosses the centerline of the roadway. For conduits where safety or other concerns prevent collection at the centerline, collect your point within the paved portion of the roadway over the conduit. Recall that a nightly process to the Statewide Conduit Database will populate this inventory data

R - Item 7. Status

The status of a conduit is the current operational status of the conduit.

Note: The Status Code “Proposed” represents a CFN created to replace an existing conduit or a new installation of a conduit where one did not already exist. Once installation has occurred and the initial Inventory and Inspection has been performed, the Status Code is to be updated to “Active”.

O - Item 8. Installation Date

The date, Day the conduit was put into service. Usually occurs when the construction project is finalized.

R - Item 9. Special Designation

Enter the most accurate code to describe the location of the conduit. (Cardinal direction logic)

Description
Mainline	Ramp to the Left
Side Road Left	Ramp to the Right
Side Road Right

R - Item 10. Conduit Owner

Enter the code for the agency who owns the conduit. Refer to Item 9 codes.

R - Item 11. Maintenance Responsibility

Enter the code for the agency responsible for the maintenance of the conduit.

O - Item 12. Entry Class

Enter the Entry Class that indicates how you performed your Inspection.

Class A (Non-Entry Inspection)
Class B (Non-Permit Required Entry)
Class C (Alternate Entry Permit Required)
Class D (Permit Required)

Entry definitions have been established to detail the requirements for inventory and inspection based on these variables. Refer to Figure 1 Conduit Entry Class Flow Chart.

Entry Class A - Non-Entry Inspection

Non-Entry inspections involve gathering inventory and inspection information without entering the conduit. The inspector will perform a visual inventory and inspection of the conduit from both ends.

Non-Entry inspections can be performed on any conduit. Consideration must be given to extremely long conduits or conduits with multiple bends which prohibit obtaining a good view of the entire barrel. An entry inspection is recommended for those conduits.

If structural or other defects are noticed during the non-entry inspection, further investigation via manned-entry or remote inspection may be required.

Entry Class B - Non-Permit Required Entry

Non-Permit inspections are arms-length inspections performed on conduits that require no special provisions for confined space issues.

Entry Class C - Alternate Entry Permit Required

Alternate entry inspections are arms-length inspections performed on conduits that require Alternate Entry Procedures to be followed. Refer to Appendix K of the current Manual of Bridge Inspection.

One requirement for Alternate Entry is that the conduit doesn’t have a known history of atmospheric or physical hazards. The inspector should make every effort to research prior inspection reports and contact the county maintenance forces to investigate any potential problems that may exist at the site.

Entry Class D - Permit Required

Permit required conduits require the full use and implementation of the Confined Space requirements.

Confined Spaces ‐ Entry of some conduits or storm drains may pose OSHA requirements regarding confined spaces. Employees must follow the protocols established by their employer when working in and around confined spaces.

Depending on their size and configuration, some conduits may meet the definition of being considered a confined space per OSHA (29CFR1910.146). Therefore, inspection procedures will vary with regard to the safety measures used.

ODOT employees are not to enter an Entry Class D conduit unless they have been trained in and are following the requirements and procedures described in the Alternate Entry Procedures for Conduit Entry, Appendix K of the current Manual of Bridge Inspection or an ODOT approved Confined Space Entry Program.

Where manned entry is not permitted or is undesirable, inspection via remote video equipment may provide a reasonable alternative.

Confined Space training is not an objective of this course, but it is highly recommended for inspectors.

• Permits can be obtained from the District Safety person.
• Most confined space inspection scenarios can be performed following the Non- Entry Inspection: Looking into the conduit from each end. In doing so, there will be no need to follow confined space requirements.

O - Item 13. Feature Intersected

Enter information that will help locate the conduit: Stream, canal, or tributary name. References to landmarks are also acceptable. Example: “200 ft. South of intersection with Parker Road.”

3. Conduit

R - Item 14. Number of Cells

Enter the number of conduit cells. Reference Item 18. Span for guidance on determining when multi-cell conduits are to be grouped as one conduit or considered separate conduits.

R - Item 15. Broken Back

A broken back conduit has more than one slope. Enter “Yes” for a broken back configuration. Enter “No” for a non-broken back configuration.

R - Item 16. Conduit Shape

Enter the most predominate shape code from list below. If the conduit was extended, do not enter the extension shape.

R - Item 17. Conduit Material

Enter the most predominant material. If the conduit was extended, do not enter the extension material. For slab top conduits, enter the material of the slab. Refer to Appendix D for photos of the various materials.

R – Item 18. Span

Unit of Measure = Inches. Use the manufacturer’s nominal pipe size. The span is the distance between inside faces of the barrel walls perpendicular to the centerline of the conduit. For a slab type culvert, the span is the distance from inside face to inside face of the abutment walls, perpendicular to the centerline of the culvert. In the case of multiple cell conduits, the conduit is considered one conduit if the distance between adjacent barrels is < ½ the diameter of the smallest barrel in the group.

R – Item 19. Rise

Unit of Measure = Inches. Use the manufacturer’s nominal pipe size. Enter the maximum rise of the conduit to the nearest inch.

If the conduit Shape is circular do not enter a value for Rise.

R - Item 20. Length

Unit of Measure = Feet. Enter the length of conduit barrel, including any extensions, from inlet to outlet to the nearest foot.

Note: If a conduit has been extended, Item 20. Length is to be edited to include the extension length(s). Example: An existing 60 ft. conduit is extended by 10 feet on each end. Edit Item 20. Length = 80 ft.

O - Item 21. Metal Gauge Thickness

Enter the gauge number for metal conduits. If different gauges exist for a conduit, heavy gauge bottom plates with lighter top plates, enter the heavier gage thickness. Enter the wall thickness, rounded to the nearest inch, for concrete, clay, or plastic conduits.

O - Item 22. Type of Pipe Protection

Enter the code for the type of protection present on the inside of the pipe.

R - Item 23. Skew (Degree)

Enter the Skew Angle of the conduit to the nearest degree. Disregard Skew Angle for longitudinal storm drains. Please note in the comments if the conduit is a longitudinal conduit.

NOTE: The Inspector should be aware of the effect of skew angle on the parallel span as measured parallel to the roadway centerline. Any parallel span ≥10 feet as measured parallel to the roadway centerline is to be placed in the Bridge Inventory and is not to be included in the conduit inventory.

C - Item 24. Centerline Span

Use the Skew Angle to determine the Centerline Span as measured parallel to the roadway centerline.

Centerline Span = Conduit Span / Cosine(Skew)

Example:

Span = 108 inches / Cosine 30
Span = 124.7 inches
Span is greater 120 inches (10 feet) = Bridge

R - Item 25. Inlet End Treatment

Enter the appropriate inlet end treatment. Refer to End Treatments listed below.

R - Item 26. Outlet End Treatment

Enter the appropriate outlet end treatment. Refer to End Treatments list above.

R - Item 27. Maximum Height of Cover

Unit of measure = feet. Enter the maximum height of cover to the nearest foot measured from the top of the conduit to the top of the pavement or embankment surface.

R - Item 28. Scour Critical

Enter yes or no. Conduits that have a spread footing are scour critical. Sound engineering judgement must be used to identify additional Scour Critical conduits.

NOTE: Items 29 through 32 are meant for conduits with a full height headwall. These 4 fields must be populated if there is a chance that the conduit is headwall critical.

O - Item 29. Height of Inlet Headwall (B)

Enter the Inlet headwall height to the nearest foot. Refer to Figure 5 Headwall Critical.

O - Item 30. Inlet Headwall to Edge of Pavement (EOP) Distance (A)

Enter the horizontal distance from to the edge of pavement to the back of the headwall to the nearest foot. Refer to Figure 5 Headwall Critical.

O - Item 31. Height of Outlet Headwall (B)

Enter the outlet headwall height to the nearest foot. Refer to Figure 5 Headwall Critical.

O - Item 32. Outlet Headwall to Edge of Pavement (EOP) Distance (A)

Enter the horizontal distance from to the edge of pavement to the back of the headwall to the nearest foot. Refer to Figure 5 Headwall Critical.

R - Item 33. Atmospheric or Physical Hazard

Enter Yes or No. If a known atmospheric or physical hazard exists enter Yes.

R - Item 34. Abrasion Level

Refer to the Abrasion Levels and Materials matrixes below and Appendix C. Select the Abrasion Level based from the General Site Characteristics. Use Level 1 if non-abrasive.

Sand: 0.002 inches – 0.08 inches
Gravel: 0.08 inches – 0.16 inches
Pebbles: 0.16 inches – 2.5 inches
Cobbles: 2.5 inches – 10 inches
Boulders: 10 inches or greater

Refer to APPENDIX C – Abrasion Level Pictures

O - Item 35. pH

Typically, only the pH of a culvert is taken. Enter the pH of the water at the inlet of the culvert to the nearest tenth.

O - Inventory Comments

A comments section is provided for the inspector to note any other inventory details not listed in the provided categories.

O - Item 36. Modification Type

Modifications may be made to conduit that do not involve the complete removal and replacement of the existing conduit. Conduits might be relined, field paved, or otherwise modified, but retain the same Conduit File Number.

If an existing conduit is relined, Code R, you must edit the Inventory R - Item 17. Culvert Material to reflect the relining material. Additionally, provide a comment in the Inventory Modification Comments field stating the material of the host conduit. Example: If a Corrugated Metal Pipe has been relined with a Corrugated Plastic, Smooth Interior pipe, edit the Inventory R - Item 17. Culvert Material to Code 13 Corrugated Plastic, Smooth Interior and add a comment stating the host conduit is a Corrugated Metal Pipe.

Modification Types
Field Paving
Section Repair
Internal Band(s)
Extending Conduit
Pipe Liner
Spray Applied Pipe Liner
Other modifications

O - Item 37. Year Modified

Enter the last year of a major repair or rehabilitation of the conduit. Leave field blank if unknown.

O - Modification Comments

The Modification Comments section may be auto populated based on historic Inventory Modification data already in the system. Additionally, recall Item 36. Modification Type requirement to include material of the host conduit here.

C - Inventoried By & Inventory Date

The Collector App will use your login as your signature and when you submit your Inventory, it will be time and date stamped.

Note: The Conduit Inspector must meet the qualifications listed within Section III Conduit Inspection of this manual.