Speed adaptation — something drivers should be aware of

Have you noticed how fast traffic moves when entering our rural villages, where the posted speed limits are normally 30 mph? This is also where enforcement sets up with radar. Measurements show speeds generally in the 40s as vehicles enter our villages. There is a reason for this, and it is called “speed adaptation.”

Tom Vanderbilt, in his book “Traffic — Why We Drive the Way We Do,” explains that the longer we drive at high speeds, the harder it is for us to slow down. The reason is that neurons in the brain that track forward movement begin to become fatigued as a person looking ahead drives at the same speed for a time. The fatigued neurons begin to produce, in essence, a negative “output,” which fools you into thinking you are moving slower than you actually are.

Because of this, as we approach a slower speed zone after a period of time at 55 or 60 mph, as we slow to the 40s, it feels like we are going much slower, perhaps even at the 30 mph speed limit. In essence, we UNDERESTIMATE our speed when asked to slow down and OVERESTIMATE our speed when asked to speed up. As Vanderbilt explains it, this is the reason why we often go too fast entering villages or coming off a highway, and also explains why drivers entering a highway frequently fail to reach the speed of traffic by the time they are merging into traffic already on the highway, frustrating those in the right-hand lane who are forced to slow down to let them merge.

So now that we have identified a real problem, how do we correct for it? We can use pilots as a good example. They rely on their instruments rather than on what it feels like, and for good reason. A pilot’s instruments tell him whether the aircraft is turning, climbing, descending, air and ground speed, and much other information necessary for safe flying. What we as drivers should do is similar — look at the speedometer. Don’t rely on what speed it “feels like.” You may be going much faster than you think, or you may be driving too slowly for some conditions, such as a merge onto an expressway. It is also important to know the change in the posted speed zone you are leaving and the one you are entering, or perhaps the suggested exit ramp speed as posted on a warning sign as you exit an expressway.

State highways are required to have, and many county and local roads also have, warning signs in advance of curves requiring a speed slower than the posted speed limit. As you approach the curve, check your speedometer — you may be going faster than it feels like and much too fast for the curve.

Vanderbilt states that the reason we have speedometers, and why you should pay attention to yours, is that drivers often do not have a clue about how fast they’re going — even when they think they do. A New Zealand study measured the speed of drivers as they passed children playing with a ball and waiting to cross the street. When questioned, drivers stated they were going at least 20 kilometers per hour (12 mph) slower than they actually were. They thought they were doing 18 to 25 mph when they were really doing 31 to 37 mph. Point made! The speedometer is accurate — our senses are not. This explains why, when changing from higher speeds to lower speeds, we can be fooled into thinking we have slowed more than we really have. Check the speedometer so you’ll know. Only a foolish, and perhaps fatal, pilot would rely on his senses over his instruments. Perhaps the same can also be said for a foolish driver.


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