SPEED LIMIT
Introduction
The Preble County Engineer’s Office gets many requests to lower speed limits on
a number of different types of roads within the county. This page better
describes the reason for speed limits and the process of changing speed limits,
especially those on county and townships roads and streets.
Authority to set speed limits
In Ohio, basic speed limits are set in accordance with Ohio Revised Code Section
4511.21. These are considered “prima facie” limits, that is, they are subject to
change when information can be supplied that would justify a change. Authority
to change speed limits in various jurisdictions is as follows:
State
Highways, including Interstate Highways and State Highways inside cities and
villages: by Ohio Department of Transportation
City
and village roads and streets other than state highways: by the city and village
through engineering study
· County
and township roads and streets: by Ohio Department of Transportation through
engineering study provided by the county or township (working with the county)
Maximum speed limits in Ohio
Interstate highways and expressways have a maximum speed limit of 65 miles per
hour. Other highways outside villages and cities, that include county and
township roads, have a maximum speed limit of 55 miles per hour. City and
village streets, including state highways within their boundaries, have varying
limits based on land use.
Factors considered in establishing speed limits
Traffic
characteristics inconsistent with particular land use or other conditions.
Prevailing
speeds consistently higher or lower than the statutory speed limit.
Transition
between rural and urban areas on major highways.
Schools
or other significant pedestrian traffic areas.
Road
construction activity.
Frequent
collisions in which speed is a contributing cause.
Unusual
or unanticipated conditions.
After a speed limit is established, there may be changes in conditions that
could lead to further traffic engineering study to determine if it needs to be
raised or lowered.
Correlation between speed limits and crashes
Attention and behavior varies from driver to driver. Therefore driver
expectations differ, leading to different traveled speeds on a section of a
road. The goal of the speed limit is to indicate to motorists a reasonable speed
under good conditions that will provide adequate reaction and stopping time on
that road. This in turn leads to more uniform travel speeds that reduce
tailgating and lane changing, major causes of traffic crashes.
Traffic Engineering Studies
Traffic studies are compilation of data that reflect actual traffic conditions
and roadway characteristics and also include an analysis using long accepted
engineering principles to determine an appropriate speed limit. Traffic studies
used to determine changes in speed limits are often called speed studies.
Characteristics used include:
Traffic
volumes
Number
and types of intersecting roads, streets and other access points
Roadway
and road shoulder widths
Traffic
crash history
Prevailing
speeds (85th percentile)
85th percentile speed
The 85th percentile speed is the speed at or below which 85 percent of the
motorists drive on a given road when unaffected by slower traffic or poor
weather. This speed indicates the speed that most motorists on that road
consider safe and reasonable under ideal conditions. This is used as an aid to
set the appropriate speed limit for that road.
Speed concerns in residential areas
Enforcement of speed limits is the responsibility of various law enforcement
officials. Requests to patrol these areas can be made to the appropriate
agency. Bear in mind that most motorists in a residential area probably live in
that area. They are accustomed to conditions and travel a speed that is believed
to be safe and reasonable. However, it is quite common for residents to believe
that traveled speeds are greater than actually being traveled. If the speed
limit is determined in the proper manner, and there is evidence of excessive
speeds, the appropriate law enforcement agency should be contacted so that speed
limits on that section of road may be enforced.
If attempts at enforcement do not achieve desired results, further investigation
from the responsible agency should be requested. Conditions may justify a
lowering of the speed limit, but may also require use of other techniques. These
would be determined through different types of traffic studies that could lead
to use of other traffic control devices and improvements. For county roads,
those requests would be directed to the Preble County Engineer. For township
roads, requests should be directed to the Board of Township Trustees of the
particular township. They will usually seek assistance from the Preble County
Engineer in assessing the problem.
The difference between the posted speed limit and advisory speeds
Posted speed limits are for ideal conditions. It is the responsibility of
motorists to maintain control of their vehicle at all times. Speeds should be
adjusted for weather conditions, at night, and for hills and curves. On county
and township roads, speed limits are enforced based on a prima facie limit of 55
miles per hour where no speed limit sign is posted. Where the speed limit has
been lowered, such a sign will be installed for that particular stretch of road.
This sign would have black letters on a white background.
Many times advisory speeds are posted at hills, curves, intersections and other
potential hazards to assist motorists in maintaining control of the vehicles.
These are usually small placard signs with black letters on a yellow background
placed under a larger warning sign. These are not specifically enforced, but
ignoring these signs may be considered as a contributing factor in an accident
if investigation shows this.