The Ramifications of Lowering and Raising the Speed Limits




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The Ramifications of Lowering and Raising the Speed Limits


The research conducted by the U.S. Department of Transportation, in the year 1992 begins with these objectives:  Determining the effects of raising and lowering the speed limits, driver behavior; and accidents from non-limited access rural and urban highways.


Data was collected from 22 states, utilizing 100 collection sites.  This critical data was collected before and after the speed limit signs were switched around.   Simultaneously the same data was collected at 14 sites that did not change the speed limit signs.  Repetitive measurements were collected to examine and determine the short and long term effects of the speed limit changes.


Speed limits were raised as much as 20 mph and lowered as much as 15 mph.  Data collected shows lowering speed limits below the 50th percentile doesnít decrease accidents it simply increases traffic violations on the main operator of a vehicle which is: the driver. Ultimately the study shows increasing the speed limit does not increase the speed of the driver nor does it increase the amount of accidents on the highways of America.


In recent years studies have emphasized on the effects of 55 mph and 65 mph, this study focused on highways that were posted between 20 mph and 55 mph.


 A maximum speed limit is posted by state statute considering: a good road, traffic along with possible weather conditions.


Previous United States legislation implies regulations were set to improve the safety of the public. The government leans towards punishing drivers who exceed the limitations set theorizing damage will be prevented towards a personís property or personal body parts attached to a human body.


The law set in place also recognizes that the maximum speed varies according to traffic conditions. The law also depends on the drivers to use their best judgment on the safety of their equipment and of course their own lives.


Prior research has shown that acceptable risk is in the 85th percentile speed.


Most traffic engineers agree that the speed should be set at a speed which is considered to be safe by the majority of the drivers, using the road ways under good weather conditions.


Most states use the 85th percentile to set the speed limit, they also take into consideration roadside development and other variables.


The lack of nation wide uniformity has left several engineers accusing some states of setting up speed traps. The primary reason states set lower speed limits is because they believe that this action will reduce speeds and traffic accidents. 


Also some law makers make the assumption that most motorist drive 5 to 10 miles over the posted speed limit any way, so lowering the speed limit will compensate for the variation.


People do die in higher speed traffic accidents due to: Kinetic energy dissipated due to the proportional square of the velocity involved.  However researchers have found being involved in an accident is much more likely when traveling at a much lower or higher speed than the majority of the motorist sharing the same highway.


Unrealistic speed limits increases traffic accidents because people totally disregard the posted limit, this gives road users and pedestrians a false perspective of the actual traffic speed.


This obscure variance in the speed limit forces judges to punish professional, average and the high risk in-experienced drivers equally. Itís quite obvious law makers, highway administrators enforcement officials, the judiciary system and the public need factual information.


Article is attached simply click this link.


Sources:  U.S. Department of Transportation, Report No. FHWA-RD-92-084 1992 Retrieved: January 18, 2006, from:




 Performing Organization Name and Address:
Martin R. Parker & Associates, Inc.
38549 Laurenwood Drive
Wayne, Michigan 48184-1073

Sponsoring Agency Name and Address:
Office of Safety and Traffic Operations R&D
Federal Highway Administration
6300 Georgetown Pike
McLean, Virginia 22101-2296

Contracting Officer's Technical Representative (COTR): Howard H. Bissell, HSR-30 and Davey L. Warren, HSR-10.
Contract or Grant Number: DTFH61-85-C-00136.
Type of report and dates covered: Final, October 1985 - June 1992



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