The Importance of Speed Limit and Lane Width for Traffic Safety By Seth Chalmers, PE

Posted on January 21, 2013


Speed is one of the most important risk factor to take into consideration when thinking about traffic safety. The faster a car is going, the more likely a crash will be more severe or even fatal, especially if a road is not suitable for those high speeds. However, the tendency of many agencies, due to a lot of factors, is to set the post speed limit high.

For this reason, it is important to consider the width of the lane. Typically, on higher speed roadways, traffic lanes should not be wider than 12 feet and not narrower than 11 feet. If additional pavement width is available, once lane widths like this are achieved, then it should be used to create the shoulders as wide as possible. Wider shoulders can reduce run-off-the-road (ROR) crashes. Even an additional foot and half can make a difference. Also, providing a graded gravel shoulder, which is completely clear of all obstructions, for additional recovery area can also greatly enhance safety

When considering the speed limit and the layout of lanes and shoulders of a roadway, it is important to take all of these factors into consideration to maximize safety.

About the Author:
Seth Chalmers is President of Chalmers Engineering Services, Inc., a traffic and transportation engineering consulting firm. Seth Chalmers has studied the impact of narrowing traffic lanes to increase the hard shoulder size and has planned and implemented several related projects.

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