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. State law and city ordinance have established specified speed limits, called prima facie speed limits, which varies according to certain roadway characteristics. 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.
Although state law gives municipalities the authority to lower speed limits below the established prima facie speed, this should only occur after a traffic 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.
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 (210.207.6000) or make a report online.
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 or retrofit the installation of traffic calming features, such as pavement markings.
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.