01334326

Component

Discussions of speed zoning focus almost exclusively on inducing the desired response by drivers. However, speed limits also get used for a variety of other applications over which the posting agency has no control and of which it may be ignorant. Posted limits may be used to determine sight distances, traffic signal clearance times, and the selection and placement of warning signs. However, to assume that they represent or control actual travel speeds is usually incorrect and can lead to the creation of adverse conditions inimical to road safety. A survey was made of the available literature, codes, and manuals to get an idea of the extent of the potential problems. Several earlier reports acknowledge posted speed limits are generally well below the prevailing (85th percentile) speed. Many found them to be near to, or lower than, the 50th percentile. Others indicate that the average for urban/suburban roads is below the 30th percentile and for rural highways below the 60th percentile. The posting or lowering of speed limits is not a safety measure and unless speed limits are posted at or above the 85th percentile speed, they misinform engineers, planners and the general public by indicating that travel speeds on a road are slower than they actually are. Bad information leads to bad results. Their potential to create unsafe conditions should not be minimized. Though the consequences of establishing improper speed limits may be unintended, they are not unforeseeable.

01329018

11-1561

English

10p

2011

Transportation Research Board 90th Annual Meeting

DVD

Figures (1) ; References; Tables (2)

Automobile drivers; Behavior; Highway safety; Rural areas; Speed limits; Speed zones; Suburbs; Traffic engineers; Traffic law enforcement; Traffic speed; Urban areas

Highways; Operations and Traffic Management; Safety and Human Factors; I73: Traffic Control; I83: Accidents and the Human Factor

Transportation Research Board Annual Meeting 2011 Paper #11-1561

TRIS, TRB

Feb 17 2011 5:51PM