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Speed Limits - Percentile Speed and safety

Does a speed limit set at the 85th percentile speed satisfy everyone?

In few other ways does society ask and expect behavioral consistency such as it does in driving on our streets and highways. But drivers' skills, attitudes, and time pressures vary greatly, as does their perception of an appropriate speed limit. Whatever the speed limit, some will consider it to be too high; others, too low. What the public should expect and demand is that, within the latitude provided in Maryland law, engineers set the most appropriate speed limits on the basis of thorough engineering study and the application of sound traffic engineering principles.

If motorists speed through a residential neighborhood, what should be done?

First, consider that traffic in most residential neighborhoods is comprised principally of those who live in those neighborhoods and who are most familiar with the street, the traffic characteristics and other conditions that affect the safe speed. Nevertheless, it is human nature for some to feel that the maximum safe speed for their street is much lower than for similar streets.

If the speed limit appears to be appropriate, but speeders are creating a safety hazard, it likely is an enforcement matter. Contact the law enforcement agency having jurisdiction over the street and ask that speeds be checked and appropriate enforcement action taken.

If, in light of the information provided in this brochure, the speed limit itself seems to be unrealistically high, contact the traffic engineering agency having jurisdiction – all of the large political subdivisions have a traffic engineering office. If there is no such office, contact the law enforcement agency.

What if those steps fail to achieve appropriate speeds?

Sometimes circumstances in certain residential areas require still slower speeds than can be achieved by posted speed limits, other traffic signing and/or enforcement. Under those circumstances, traffic engineering studies might determine that "traffic calming" techniques, such as roundabouts, chokers, speed humps (not speed bumps), raised crosswalks, pedestrian refuge areas, or other physical controls, can reduce speeds and make street-crossing easier and safer.

Is it always safe to drive at the speed limit?

As described, speed limits typically are set for ideal conditions. Therefore, drivers must recognize and appropriately respond to adverse conditions. Maryland vehicle law requires that motorists drive at a reasonable and prudent speed and with a regard for existing and potential dangers. Motorists must adjust their speed according to the existing vehicle and pedestrian traffic, road surface, lighting, and weather conditions. Maintaining a safe speed at all times is a serious responsibility shared by all motorists.


State Highway Administration
Office of Traffic and Safety
Traffic Safety Division