Speed Limit Signs
Does Lowering the Speed Limit Solve a Speeding Problem?
Municipalities and other agencies, which are responsible for traffic control, are occasionally asked by citizens to reduce the posted speed limit after a traffic problem has been identified. Citizens hope that the lower speed limit will reduce operating speeds and accident potential. Although public agencies share the desire for lower speeds and improved safety, studies have shown that arbitrarily reducing the speed limit does not accomplish the desired result.
Research has shown that lowering regulatory speed limits does not result in lower operating speeds nor in reduced accident potential. By and large, drivers chose their speed independent of the posted speed limit. Drivers select their speed intuitively based on the environment around them and the speed that feels comfortable and safe. "Before and After" studies have shown that there are no significant changes in average vehicle speeds following the posting of revised speed limits.
There are essentially two problems that may be associated with speed limits that are set too low. First, accident potential may increase due to the greater speed differential that exists when speed limits are posted unreasonably low. The safest traffic condition occurs when all vehicles travel approximately the same speed. Second, state law and city ordinance have established the prima facie speed limit which varies according to certain characteristics of the roadway. Although state law gives municipalities the authority to lower speed limits below the established prima facie speed, this should only occur after a traffic and engineering study suggests that the lower speed limit is appropriate. In the absence of such a study, a regulatory speed limit that is lower than the prima facie speed limit constitutes a "speed trap" and may be unenforceable in court.
Speed limits are set on the 85 percentile speed of a roadway. What this means is that the speed limit is the speed at which 85% of drivers feel comfortable driving. This method has been proven to be safe, practical and enforceable.
Residential Speed Limits
States base their speed regulations on the Basic Speed Law: "No person shall drive a vehicle...at a speed greater than is reasonable or prudent...and in no event at a speed which endangers the safety of persons or property."
Under Texas law, a motorist "may not drive at a speed greater than is reasonable and prudent under the circumstances then existing." In addition, specified speed limits, called prima facie limits, are considered by law to be reasonable and prudent under normal conditions. Certain prima facie limits are established by State law including the 30 mph speed limit on streets and the 15 mph speed limit on alleys in urban areas. These speed limits do not need to be posted to be enforced. Streets that have speed limits higher than this base speed limit are signed as 35 mph zones, 40 mph zones, 45 mph zones, etc. Streets that do not have these signs are 30 mph zones.
30 mph speed limit signs are installed generally under any one of the following criteria:
- streets that have documented speeding problems,
- streets that appear to motorists to have a faster speed limit (e.g., very wide streets), or
- streets that are the primary entrance into a residential subdivision where the interior streets are all 30 mph zones.
Drivers are required by the Texas Department of Public Safety to possess a valid Texas Drivers License. Obtaining a license requires knowing that the prima facie speed limit on city streets is 30 mph, unless otherwise posted.
35MPH and Faster Speed Zones
On any given street, some vehicles operate at faster speeds than others. The street’s operating speed is characterized by the statistically derived 85th percentile speed. This is the speed at, or below, which 85 percent of the vehicles travel. Non-residential streets can have speed limits that are faster than 30 mph. Factors that are considered in the establishment of the speed limit are the 85th percentile speed, adjacent land use, roadway character, 12-month accident history and engineering judgment.
Requesting Speed Limit Signs
If you are interested in having the City add speed limit signs to a particular street that meets the criteria outlined above, or if you wish to get the City’s assistance in determining if a particular street qualifies for speed limit signs, you may call 311 or make a report online through City Connect - Online Services.
Getting Motorists to Drive Slowly
Installing speed limit signs often does not cause motorists to drive at reasonable speeds. In fact, motorists tend to drive at speeds they feel comfortable with, regardless of the speed limit. Consequently, to cause vehicles to operate at lower speeds it may be necessary to increase enforcement of the speed limit law or retrofit the installation of a traffic calming features, such as pavement markings or signs.
What You Can Do
Most of the motorists who speed on our City streets are fellow residents. If additional measures are needed to provide sufficient traffic safety, please contact call 311. If we all do our part to follow the speed limits, we will improve traffic safety for San Antonians and our visitors.