Ohio.gov State Agencies  |  Online Services
Skip Ribbon Commands
Skip to main content
Sign In

Speed Zone Studies

See ODOT Application Standard 5A-4, Revised August 22, 2001. This application standard describes the complete process that is required when doing a speed zone study.Note: This is a large document.

Why Speed Limits?

Since most citizens can be relied upon to behave in a reasonable manner as they go about their daily activities, many of our laws reflect observations of the way reasonable people behave under most circumstances. Traffic regulations are invariably based upon observations of the behavior of groups of travelers under various conditions.

Generally speaking, traffic laws that reflect the behavior of the majority of vehicle operators are found to be successful, while laws that arbitrarily restrict the majority of drivers encourage wholesale violations, lack public support, and usually fail to bring about desirable changes in driving behavior. This is especially true of speed zoning.

Speed zoning is based upon several fundamental concepts deeply rooted in our American system of government and law.

Driving behavior is an extension of social attitude, and the majority of drivers respond in a safe and reasonable manner as demonstrated by their consistently favorable driving records.

The normally careful and competent actions of a reasonable person should be considered legal.

Laws are established for the protection of the public and the regulation of unreasonable behavior on the part of individuals.

Laws cannot be effectively enforced without the consent and voluntary compliance of the public majority.

Public acceptance of these concepts is normally instinctive. However, the same public, when emotionally aroused in a specific instance, will often reject these fundamentals and rely instead on more comfortable and widely held misconceptions, such as:

Speed limit signs will slow the speed of traffic.

Speed limit signs will decrease the accident rate and increase safety.

Raising a posted speed limit will cause an increase in the speed of traffic.

Any posted speed limit must be safer than an unposted speed limit, regardless of the traffic and roadway conditions prevailing.

"Before and After" studies consistently demonstrate that there are no significant changes in traffic speeds following the posting of new or revised speed limits. Furthermore, no published research findings have established any direct relationship between posted speed limits and accident frequency, although short-term reductions have resulted from saturation enforcement efforts directed at speed and other traffic law violations.

Police agencies necessarily rely on reasonable and well recognized speed laws to control the unreasonable violator whose behavior is clearly out of line with the normal flow of traffic.

Contrary to popular belief, speed in itself is not a major cause of accidents. In fact, there is a consensus of professional opinions that many speed-related accidents result from both excessively low and high speeds.

It is accepted within the traffic engineering profession that there is a demonstrated need to produce as much uniformity as possible in the traffic flow and to eliminate the so-called speed trap. A speed trap may be defined as a street or road which is wide enough, straight and smooth enough, and sufficiently free of visibility limiting obstructions to permit driving a certain speed, but where the law nevertheless calls for a much lower speed.

Why Should I Care About Realistic Speed Limits?

Realistic speed limits encourage drivers to travel at a safe speed

Realistic speed limits encourage drivers to obey the posted speed limit

Realistic speed limits clearly show the reasonable and prudent speeds

Realistic speed limits make it easier for police to enforce the speed limit

What’s Wrong With a Speed Limit That is Too Low?

Unrealistically low speed limits DO NOT SLOW DOWN CARS!

Unrealistically low speed limits may increase the potential for crashes.

Unrealistically low speed limits encourage drivers to break the law and may encourage drivers to disobey other signs.

Unrealistically low speed limits make people think they have been caught in a "speed trap".

Unrealistically low speed limits make people angry at police officers.

Unrealistically low speed limits create a bad image for a community in the eyes of visitors.

What is a Rational Speed Limit?

Good traffic laws reflect the behavior of the majority of motorists. Traffic laws that are not based on the behavior of the majority of drivers encourage violations. This is especially true of speed limits.

Speed zoning is based on four fundamental American legal concepts:

Most drivers are safe and reasonable.

What a reasonable person does should be considered appropriate.

Laws protect the public and reduce unreasonable behavior.

Laws can only be enforced with the consent and voluntary compliance of most people.

A rational speed limit is one that is safe, that most people consider appropriate, that will protect the public, and that can be enforced.

Common Misconceptions

You probably nodded your head to the concepts listed above. They make good sense. When it comes to controlling speed, however, we tend to fall back on truisms that turn out not to be true at all. Like:

 "A lower speed limit slows people down."

"A lower speed limit decreases crashes"

"A higher speed limit makes people speed up."

"Drivers always go 5 MPH over the speed limit."

How Are Speed Limits Set?

The "85th percentile speed" is a basic factor in setting speed limits. Basically, traffic engineers measure vehicle speeds, and then determine the speed that 85 percent of the drivers were at or below. The 85th percentile speed is how drivers "vote with their feet".

Studies have shown crash rates are lowest around the 85th percentile speed. Drivers traveling significantly faster OR slower than this speed are more likely to crash. High speeds do not determine crash risk - the difference among the speeds of vehicles does. It is true that crashes at higher speeds tend to be more severe, but higher speeds to not necessarily increase the likelihood of a crash.

In fact, high-speed roadways, like interstate highways, have a lower speeding- related fatality rate than low speed roadways. Large variations in speed within the traffic stream create more conflicts and passing maneuvers, which lead to more crashes.

What Other Factors Are Considered?

Other factors are considered in setting the final speed limit, such as: crash history, curves, number of driveways and cross streets.

But the Cars are Still Going Too Fast on My Road

If the 85th percentile speed is just too fast, posting a lower speed limit sign doesn’t make drivers slow down. Other means of making drivers move more slowly on a neighborhood road, called "traffic calming" are needed. Traffic calming includes adding features to the road that actually force drivers to drive more slowly.

Remember, self-enforcing, reasonable speed limits that reflect the behavior of most drivers are most likely to lead to safe roads and allow police to focus their efforts on stopping the most flagrant violators.

How Realistic Speed Limits are Established in Ohio?

Section 4511.10 of the Ohio Revised Code (ORC) establishes ODOT's authority to place and maintain traffic control devices conforming to the OMUTCD on all state highways, and indicates that "no local authority shall place or maintain any traffic control device upon any highway under the jurisdiction of the department except by permission of the director of transportation."

Section 4511.21 of the Ohio Revised Code (ORC) establishes Speed Limits for all streets and highways within the State. It also provides that the Director may alter Speed Limits. It further provides that local authorities may request that the Director determine and declare a reasonable and safe speed limit.

More Frequently Asked Questions on Speed Limits

Procedures for Authorizing Speed Zones

ODOT-Maintained Highways

All proposals for alterations of speed limits on ODOT-maintained highways shall be documented with the appropriate engineering study as outlined in Part 5 of the OMUTCD and Section VI herein.

Once a determination has been made to alter a speed limit, the District shall forward the proposed speed limit reduction to the appropriate District Office of the Ohio State Patrol (OSP) for review and comment.

Following resolution of the OSP comments, if any, the District shall prepare a description of the Speed Zone for the Director's approval using the Speed Limit Revision form.

Following approval, the District shall erect the appropriate Speed Limit signs, record the dates on the description, and notify the OSP and other law enforcement agencies as appropriate.

Local Roads

All requests for alterations of speed limits on local roads shall be submitted to the District in the form of a resolution of the local authorities. The appropriate engineering study, as outlined in Part 5 of the OMUTCD and Section VI herein, shall be included with all such requests. Concurrence from the appropriate enforcement agency should be included with the study. All requests shall be acknowledged, and the local authorities shall be notified whether additional data will be necessary to substantiate their request.

Based on the engineering study, the District shall determine a reasonable and safe speed limit. If this determination is substantially different from that which was requested, the local authorities may be asked to further substantiate their original request, and a new determination may be made.

Following resolution of any comments, the District shall prepare a description of the Speed Zone for the Director's approval using the Speed Limit Revision form.

The District shall notify the local authorities of the Department's final action on the proposed Speed Zone.

If, based upon the District's final determination, new Speed Limit signs are required, the local authorities shall erect the signs and, upon completion of the work, forward the signed Speed Limit Revision form to the District and notify the OSP and other law enforcement agencies as appropriate.

Upon receipt of the completed authorization form, the District will forward the completed Speed Limit Revision form to ODOT's Central Office, Office of Traffic Engineering.

For more information on Speed Management, try the FHWA Safety Website at:  http://safety.fhwa.dot.gov/programs/speedmgnt.htm