Vision Zero, VZ, has a very admirable goal: Reduce traffic fatalities to zero.
We could accomplish that by not having traffic at all, but that creates its own problems. Some of their proposals are so common sense they are already policy, have been for years. Unfortunately, the implementation has not been a resounding success.
Impaired drivers are cited in the majority of crashes, although the link from impairment to causation is sometimes assumed rather than proven. The crash might be entirely the fault of something or someone other than the one cited. We measure impairment indirectly by blood analysis though the connection is imperfect. A better measurement of actual reduced performance would make more sense. Enforcement generally occurs after the crash so its value as a deterrent is mostly hope.
VZ encourages red-light-camera enforcement, which could be valuable if applied logically and not used mainly for revenue. Camera enforcement’s failures are legendary.
The VZ’s prescription is to reduce all speeds to a level that makes fatality less likely in a crash, ignoring all other considerations. This is not really new but goes against 100 years of traffic engineering scientific experience. VZ emphasizes reduced speeds and reduced speeding almost exclusively.
That would be reasonable if the legal speed limit was not arbitrary. Usually the limit is established by fiat with only political or hysterical input. The highest speed on VZ’s Hawaii would be 43 mph and on most streets 30 or less!
Reduced speed does not necessarily reduce the number of crashes, sometimes it increases them. VZ ignores the probability that this will increase the number of crashes and not-quite-fatal-injuries. This VZ policy also ignores the wasted partial lifetimes waiting in traffic instead of living. If I have just one life to live, let me live it not waiting in traffic jams.
On open highways there is a natural safe speed that can be determined by evaluation of the behavior of the hundreds or thousands of drivers using the road in good conditions. Traffic engineers have learned that not only will 85 percent of the drivers stay within reasonable criterion, but when they do so traffic is well disciplined with little conflict.
The 85th percentile of free-flowing traffic is the traffic engineering recommendation for the posted maximum highway speed under ideal conditions. There will always be some outliers eligible for enforcement. Interestingly when the speed limit is based on this criterion not only will few exceed it, over 50% will be within a narrow 10 mph range. There will be a few laggards, but most of those have a reason, such as looking for an address.
Post a speed limit lower than the 85th percentile and the maximum speed of traffic hardly changes. What does change is the range of speeds. A few drivers will rigorously obey, they will be immediately followed too closely by drivers who know from experience that higher speed is practical. The probability of a rear end crash increases. Eventually someone gets impatient and tries to pass the parade not always with a good result. Increase the speed limit from 85th percentile and hardly anything changes.
There is a major flaw in the slow down philosophy. Reducing speed by a percentage increases the time on the road by a similar percentage, and therefore, more cars on the road. More opportunities to crash. Many roads are at or near capacity already. Add 15% to the volume by reducing speed from 35 mph to 30 mph and the result is gridlock or impatience-driven chaos.
That means more crashes and more injuries. The best way to avoid injuries is not go slower, it’s to not crash. When the 55 mph National Speed Limit was repealed safety advocates predicted carnage, but crashes and fatalities went down significantly while travel time was reduced dramatically.
Speed does not kill. Crashing kills. At this very moment a million people are going 600 mph at 30,000 feet with no harm.
Ken Obenski is a forensic engineer, now safety and freedom advocate in South Kona who writes a weekly column for West Hawaii Today. Send feedback to obenski@gmail.com.
