Today I will (finally) finish my comments on Tom Vanderbilt’s book, Traffic. He observes that drivers travelling 50 miles per hour are 25 times more likely to die than those driving at 25 miles per hour (p. 210).
This fact, which is well documented, has several implications for how supervising adults should deal with teen drivers. First, obviously, when you act like an air traffic controller and work with your new drivers to prepare a “flight plan” for each drive, and you consider the route, you should evaluate the likely, average speed of cars on the roads that will be taken on that drive. For new drivers, in general, the escalating risks of high speeds warn against allowing them to drive on a limited access highways with high posted speed limits (and minimums) such as Interstates, or avoiding such roads as much as possible. (However, it is important to note that divided highways, with multiple lanes travelling in the same direction and separated from opposing traffic by a barrier, are safer than highways in which the only separation between traffic directions is a pavement marking.) Second is to counsel teens, where possible, to avoid roads on which they will be able to drive at higher speeds, such as long straightaways with relatively little traffic. Conversely, though we might think that having teen drivers use congested or heavily-trafficked areas is more dangerous (and nerve-wracking) than more open roads, Vanderbilt’s observation tells us that there is actually less risk wherever traffic, whether due to speed limits or congestion, operates at lower speeds.
It is important to note that Vanderbilt’s caution is not a linear equation. Starting at 25 MPH, twice the speed increases the risk by 25 times. In other words, once a driver gets beyond the speed of a quiet residential street, the risk of a serious injury or fatality rises quickly. We should also bear in mind why higher speeds are much riskier, especially for teens: circumstances change more rapidly, there is more for drivers to keep track of, and new drivers in particular have slower reactions because they are less skilled at looking down the road to see situations developing in the distance, and their reactions to unexpected developments and safety hazards are uncertain at best.
To summarize, an important guideline for adults supervising teen drivers, especially brand new ones, is to avoid the higher speed roads, because 50 is much more dangerous than 25.