In Texas, the department of transportation is currently debating increasing the speed limit on a stretch of highway from San Antonio to Austin to 85 miles per hour. If this change is made, then this stretch of highway will have the highest speed limit in the United States. And this begs the question: What is the relationship between higher speed limits and accident frequency?
So do higher speed limits cause more accidents? In study after study, the answer is a resounding no. But when accidents occur at higher speeds, the damages and injuries are much more severe. Death rates in high speed accidents are always much higher than in those at reduced speeds. So what should determine the best speed limit for safety?
As it turns out, most studies indicate that the optimum speed limit for a highway is a speed at or below the speed at which 85% of the drivers would drive at any given location in optimum weather conditions. You see, while high speed accidents generally are more fatal and cause more damage, the factor that causes more accidents on highways is a large discrepancy between the fastest cars and the slowest cars. In turns out that most people won’t drive faster than their speed comfort zone. I know this seems a ridiculous notion given how many drivers you see texting and talking on the phone while they drive, activities that are actually much more dangerous than speeding. But people recognize that speed can kill them and will rarely drive faster than they can control their vehicle. By choosing a speed limit that suits 85% of the drivers, police can then more easily find those that are the speeding outliers who need to be controlled by ticketing.
But wait, isn’t driving slower always safer? Actually both state and federal studies have 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. Those driving 10 mph slower than prevailing speed are more likely to be involved in an accident than those traveling 10 mph faster than the average speed.
One thing that should be taken into account with higher speeds is that stopping distances are increase rather dramatically. The stopping distance for a vehicle traveling 60 mph is just over half of that of the same vehicle traveling at 85 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 a relic of old thinking that still remains in our laws. Ironically, if you can get your ticket reduced to less than 10 miles over the speed limit, then you can have the extra points on your auto insurance policy waived. But 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. 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.
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