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Lower/higher speed limits?

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Concerning the pending legislation to increase Illinois speed limits and a compromise that may leave final decisions to the counties …

Studies have long shown speed limits have little effect on how fast people actually drive on open roads, and any traffic engineer (and many state police departments) will explain 85th percentile speeds are the proper way to set limits (the maximum speed at which 85 percent of traffic actually flows when unencumbered).

Artificially low limits do not slow down the faster traffic, but they do cause several types of dysfunction which make the roads more dangerous. For example, slower traffic will tend to flow at the posted limit. When limits are too low, speed variance between the fastest and slowest traffic increases. This is a leading cause of road rage particularly when slower traffic does not keep right and yield to faster traffic. Dumbed-down limits also tend to increase distracting activities, further contributing to impaired drivers and road rage as slower traffic lumbers along in the passing lane chit-chatting on the phone, too busy to notice someone wants to pass.

In addition to road rage and speed variance being largely caused by artificially low speed limits, there are other issues. For example, Illinois instituted “super-speeder laws” a year or two ago. For going 30 over the limit, a person can go to prison. Think about that. Thirty miles per hour over the limit is not unusual in Chicagoland when the roads are clear (55+30 = 85). This is not such an unreasonable speed in modern cars in clear daytime weather that offenders should go to jail.

Combining extreme penalties like this with limits which are 20-30 mph below prevailing traffic flow speeds exposes even safe drivers to the threat of jail time and insurance rate surcharges. The insurance surcharges (for points on license) are the primary reason that P&C insurance companies (including AAA) push to keep limits low – it enables them to charge higher rates without higher risk – it’s all profit. Health, disability and life insurers have very little to say about speed limits because it is a non-issue for them.

States which have increased limits, by and large, have experienced declines in fatality rates because of reduced speed variance and road rage. The Michigan State Police are among the more outspoken proponents of this approach. The fatality rate even decreased in Montana which for some years had no daytime limit following the demise of the 55 mph national speed limit in 1995. In 1995, 22 years of prohibition ended … unless you live in Illinois.

Traffic congestion increases when speeds are lower. Heavy traffic can only move as fast as the slowest car, and the slowest car will be going the speed limit. Like water through a hose, you can increase the flow rate by using a bigger hose or by increasing the flow rate. Slow down the flow of the main line, and all the feeders back up. Lower limits mean more gridlock.

Artificially low limits have nothing to do with safety. They are about politics and enrichment of insurers.

Steve Doner, former Illinois state chapter coordinator for National Motorists Association


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