A speed zone is a section of roadway with a different posted speed limit than the statutory speed limit. The Ohio Department of Transportation (ODOT) must approve speed zones that lower speed limits on all state, federal, interstate, and local roadways. Speed zones to raise speed limits can, in some cases, be accomplished by local municipalities, without ODOT's approval.

How ODOT Sets Safe Speed Zones

It is important that set speed limits are considered reasonable by a majority of drivers. Studies have shown that most drivers tend to drive at a speed with which they are comfortable, so raising or lowering the speed limits does not have a significant effect on speed. However, when the speed limit is set at a level that most drivers consider reasonable, the speed of vehicles is more uniform, which has proven to be a safer traffic pattern.

When doing speed zone studies ODOT considers various factors such as the development of the area, roadway features, traffic volume, accidents, and the speed vehicles are traveling.  Both the 85 percentile speed and the 10 mph pace are very important factors. The 85 percentile speed is the speed at which 85% of the vehicles are traveling at that speed or lower, while the 10 mph pace is the 10 mph range of speeds containing the greatest number of observed speeds.