Do Higher Speed Limits Cause More Accidents?

The Texas Department of Transportation is in the midst of a debate about increasing the speed limit on a stretch of highway to 85 mph.   If this happens, then this section of road will hostthe highest speed limit in the United States.  Should Texas then expect to experience more car accidents on this highway then?

What is the relationship between speed limits and accident frequency?  Will higher speed limits always lead to more accidents?  In nearly every study made, the answer is no.  However, when accidents happen at higher speeds, the damages and injuries are much more severe.  Fatality rates in high speed accidents are always higher than in those at lower speeds.  Given that, how do traffic engineers determine the safest speed limit on any given stretch of highway?

Well, the formula that is most commonly used now is to set the speed limit at a speed  at which 85% of the drivers would drive at any given location in optimum weather conditions.  This is because the real factor in determining the likelihood of an accident is the speed disparity between the fastest and the slowest cars.  The majority of drivers rarely drive faster than their speed comfort zone.  This might seem ridiculous given how many drivers you see risking their life and everyone else’s by texting and talking on the phone while they drive.  These behaviors are much more dangerous than driving fast, but people understand intuitively that speed can kill them and so they rarely drive faster than they can control their vehicle.  Texting and talking on the other hand are activities that few drivers recognize as deadly at this time in our cultural development.  That will change in time.  When traffic engineers choose a speed limit that suits 85% of the drivers, then the police can then more easily spot the speeding outliers who need to be controlled by ticketing.

But wait, isn’t driving slower always safer?  Well no.  It turns out that in  both state and federal studies it is consistently shown that the drivers most likely to get into accidents are those traveling significantly below the average speed of the other drivers on the road.  If you are on the highway driving 10 mph slower than the average vehicle speed  then you are more likely to be involved in an accident than if you were driving 10 mph faster than the average speed. 

One thing that everyone should remember when driving at higher speeds is that that you need to allow significantly longer stopping distances between you and the car in front of you.  It will take you nearly twice as far to stop at 85 mph as it will at 60 mph.   So increased speed limits need to be accompanied by some changes in driver habits and that doesn’t always happen.

If those driving on highways at speeds above the speed limit are less likely to get into accidents than those traveling at speeds below the speed limit, then why do auto insurance companies charge you higher rates if you have speeding tickets on your driving record?  In my opinion this is an example of archaic rules still on the books.  Here in NC it is a bit ironic that you can get your ticket reduced to less than 10 miles over the speed limit and have your insurance points waived.  However, if you get a speeding ticket for going more than 75 mph in NC, which in some cases might be only 6 mph over the speed limit, then you could face a 4 point surcharge which would increase your insurance costs dramatically.  You can quickly see that this approach flies in the face of all research and does not make any actuarial sense at all.  I think with the increased use of on board monitoring systems for auto insurance rates, that eventually some of the speeding ticket insurance surcharges will be changed or removed from the books completely.

Clinard Insurance Group is an independent insurance agency located in lovely Winston Salem, NC.  We insured thousands of families all across North and South Carolina.  If you need any help with your auto insurance policy, your homeowners insurance policy, or your life insurance, please call our office, toll free, at 877-687-7557.  We look forward to answering your questions and helping you.