Speeding

As I was driving home from my road trip a couple of days ago, a thought occurred to me. Several cars were passing me on the highway, clearly going 10 km/h over the speed limit. Of course, people speed to save time and to get where they are going in a hurry. Sometimes they go 10 km/h over the limit on the highway, and sometimes they do the same thing in the city. I wondered, is there a difference?

More precisely, suppose you had to travel 100 km. In the first situation, you are on the highway clipping along at 100 km/h. The urge to speed wells up inside and you long to shave some time off your trip. If you increase your speed to 110 km/h, how much time do you save?

At your original speed, it will take you 60 minutes to complete the trip. At the increased speed, the trip will only take 54.5 minutes. Thus, you save 5.5 minutes on your trip. Not a ton of time, but still a temptation if you need to get somewhere in a hurry.

Now consider the second situation. You still need to travel 100 km, but you are in the city traveling at a gentle 60 km/h. Suppose you increase your speed to 70 km/h, how much time will save? Take a guess!

My first instinct was that you would still save about 5.5 minutes on the trip since the distance travelled is the same. However, if you crunch the numbers, you find the following:

Time at 60 km/h: 100 minutes

Time at 70 km/h: 85.7 minutes

Time saved: 14.3 minutes

You more than double your time savings! Let’s push this idea to the extreme. Consider a third situation, where you still need to travel 100 km, but the entire time you are stuck in a school zone and must travel 30 km/h! The kind of malicious person who would create a school zone like that escapes me. However, we will continue for the sake of the math. Here are the results:

Time at 30 km/h: 200 minutes

Time at 40 km/h: 150 minutes

Time saved: 50 minutes

You save almost an hour by speeding! Incredible and unexpected! A word of caution. I am in no way advocating speeding, it is a dangerous habit with potentially fatal consequences. However, by investigating the math of the situation, I believe I have uncovered something about human nature. While driving down the highway, speeding feels like a 50-50 choice. You could go a bit faster and cut some time off your trip. Or you could obey the speed limit. In either case, the difference won’t be that noteworthy. Yet, when people are stuck in a school zone, the temptation to speed can feel overwhelming. The vehicle is moving so slowly and it feels like going even 10 km/h over the speed limit would drastically reduce your commute. I think that this temptation, this intuition, is illuminated in the math above. Speeding in a school zone really does save you much more time than speeding on the highway.

Being a teacher, I can not, in good conscious, leave the discussion there. In the final, real life scenario, when the school zone is only 0.5 km long, here are the numbers:

Time at 30 km/h: 1 minute

Time at 40 km/h: 0.75 minutes

Time saved: 15 seconds

While it might be reasonable to try and speed through a 100 km school zone of torture, the 15 seconds saved in a regular school zone is not worth the risk of a child’s life. As the slogan goes, “normal speed meets every need.”