The one thing that no one in the transportation advocacy community wants to talk about is speed-limiting vehicles. Speed-limiting means that vehicles cannot operate over the speed limit selected for a section of roadway. The technology for doing this is largely already in place on modern motor vehicles, as they already monitor their speed and already have available information about the speed limit on the street they are on. Older vehicles of course don’t, and would need to be retrofitted.

Why speed limiting? Because it is a simple solution that cuts through all the other discussion and contortions and expense of other solutions. Some people think education is the solution, as though all the education to date has done any good. Some people don’t want any traffic laws enforced, because ‘freedom’, meaning of course the freedom to operate a vehicle recklessly and kill people. Some people think that the solution is to redesign roads so as to prevent speeding. I’m not against that solution, but our mis-designed transportation system has a value of trillions of dollars, and fixing it will require trillions of dollars. We could spend our money that way, but why when we have so many other good causes to spend on. Vision Zero efforts are admirable, at least when they don’t have the involvement of law enforcement, but there has been very slow progress or regression in the United States because the engineering profession and law enforcement really don’t believe in the idea, giving it lip service while trying to subvert it.

Speed kills. It increase the severity of crashes, making severe injury and fatality more likely. It also increase the frequency of crashes, because drivers have less time to react and avoid, or slow before impact. You have all seen a version of the graph below, and it is important to remember that at every speed, speed is a contributing factor.

Speed limited does not mean changing posting speed limits, though it turns out that reducing speed limits does indeed reduce traffic speeds and reduce crashes and injury severity. However, speed limits are not set to the design speed of the road, but lower than than. As a result, drivers are encouraged by road design to speed, while fingers are wagged and tickets are written. But the problem is not solved. Crashes and severe injuries and death continue apace, or increase in the case of this last year.

With speed-limiting, no vehicle goes faster than the speed limit. If there are no crashes, maybe it gets increased a bit. If there are crashes with severe injury or fatality, then it gets reduced. We don’t need to change speed limit signs, we just change the permissible speed which vehicles respond to and follow.

Of course we should redesign streets to make them friendlier and safer for walkers, bicyclists, transit users, and drivers for that matter. But in the meanwhile, I want no one to die or be seriously injured on the streets and roads we have. Speed-limiting is the solution.

It is worth pointing out that designers and manufacturers of autonomous vehicles don’t want this to happen. They are assuming they will be allowed to violate speed limits, because they know that their primary target driver audience, young aggressive males, won’t buy vehicles that go the speed limit. They are just hoping no one notices that they are going to bypass this, and probably will get away with it.