The Ohio Manual of Uniform Traffic Control Devices states "Section 4511.21 of the Ohio Revised Code (O.R.C.) establishes statutory speed limits, and prescribes how those speed limits may be altered when an engineering study determines that they do not fit the road and traffic conditions. The process by which an altered speed limit is established is typically referred to as speed zoning."
When setting speed limits it is important to have speed limits that the majority of drivers consider reasonable. Studies have shown that most drivers tend to drive at a speed they are comfortable with. 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. It is considered safer to have all the vehicles traveling at approximately the same speed. Also the Ohio Department of Transportation (ODOT) does not want to set unreasonably low speed limits that would make the average driver a law breaker.
When doing speed zone studies ODOT considers various factors such as the development of the area, roadway features including 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 percent of the vehicles are traveling at that speed or lower. The 10 mph pace is the ten mile per hour range of speeds containing the greatest number of observed speeds.
Speed zone requirements are for roads and streets in all jurisdictions
It should be noted that ODOT approved speed zones are needed for roads and streets that are to have a speed limit lower than the statutory prima-facie speed limits given in the Ohio Revised Code regardless of jurisdiction. This includes, rural state highways, county and township roads and streets in both cities and villages. However, a Board of Trustees has the authority to lower the speed limit without ODOT approval on a road that is an "unimproved highway" or is in an area that meets the Ohio Revised Code definition of a commercial or residential subdivision.
Raising speed limits in cities and villages
It should be noted that while both cities and villages are required to have ODOT approval to have a speed limit lower than the statutory prima-facie speed limits given in the Ohio Revised Code, they can raise speed limits on their streets without ODOT approval. The Ohio Revised Code states in part "Local authorities in their respective jurisdictions may authorize by ordinance higher prima-facie speeds than those stated in this section upon through highways, or upon highways or portions thereof where there are no intersections, or between widely spaced intersections, provided signs are erected giving notice of the authorized speed, but local authorities shall not modify or alter the basic rule set forth in division (A) of this section or in any event authorize by ordinance a speed in excess of fifty miles per hour."
Additional information on speed limits and speed zones
Section 1200 of the ODOT Traffic Engineering Manual has the forms and directions for performing speed zone studies. (requires Adobe Acrobat Reader)
Approved traffic control zones - Information on the locations of traffic control zones in all twelve Districts of the Ohio Department of Transportation for state and local roads. The traffic control zones lists include speed zones, parking zones, school zones and village signal permits.
Arizona Department of Transportation - Establishing Speed Limits - A Case of "Majority Rule"
FHWA Traffic Safety Research Program Summary Report - Effects of Raising and Lowering Speed Limits on Selected Roadway Sections
Complete Report - Effects of Raising and Lowering Speed Limits on Selected Roadway Sections (requires Adobe Acrobat Reader) Note: This file is 2.08 MB.
ODOT District One Planning & Engineering Web Site Manager: Charles Schreck