By the numbers: How following speed limits and using seat belts add up to a safer drive
Question: Is there a speed at which wearing a seat belt isn’t important because I’m going slow enough to where I won’t get hurt?
Answer: I’m pretty sure that if I answered this question with an actual number there would be people out there who treat it as a rule: “Oh, I don’t put on my seat belt until I’m going at least 13 mph.” You might think I’m joking, but there’s actual data to (sort of) support the idea.
Every year the Washington Traffic Safety Commission conducts a seat belt use observation survey. Yep, it’s just what it sounds like. Observers count how many people wear their seat belts, using enough locations and vehicles to get an accurate representation of use statewide. According to the most recent survey, 94% of vehicle occupants in Washington wear a seat belt, and it’s been at roughly that level since the early 2000s.
How is this relevant? The survey also tracks seat belt use based on road type. The rate on state routes (with generally higher speed limits) is about 95% while the rate on city streets (read slower speed limits) is about 90%. County roads fall in between. It seems that some people are, consciously or not, adjusting their seat belt use to the speed of their driving.
Before we address the flaw in the logic there, I think we can agree on the opposite; there are speeds where all the safety features available on the highest safety-rated vehicles can’t protect you from physics. The human body is a flimsy container for our consciousness, at least when you consider the speeds with which we are capable of traveling, and when your delta-v exceeds human limits there’s no seat belt or air bag that can make up for it.
At the other end, we don’t generally worry that our walking or running speeds will get us into a life-threatening situation. However, designers have developed airbag jackets for pedestrians that would deploy if they sensed that a person is about to be struck by a car. Maybe that sounds silly, but it also highlights the problem with the original question. In an 18-mph collision in a car you have a one in 10 chance of a serious injury; if you want your odds to be more like one in 100, you’d have to go slower, obviously. The problem with that number, whatever it turns out to be, is that it doesn’t factor in anyone else on the road.
Despite a steady seat belt use rate, the number of unrestrained fatalities has increased to the highest number since before 2010. Just since 2019 unrestrained fatalities have increased more than 30%. If seat belt use rates are staying the same, what has changed? It’s not more people on their phone; that number went down a bit. Most likely, it’s speed.
In the past couple years there has been a spike in the infractions written for speeding in excess of 40 mph over the speed limit. Yeah, that’s a lot over the limit. To be fair, most people aren’t driving like that, so it doesn’t take a lot of extra tickets to cause a spike, as there aren’t a lot of those issued to begin with. What it does show is that when speeds go up, so do serious crashes, even if our other driving habits remain steady or even improve a bit.
Driving at a safe speed reduces your risk of a crash, and the severity of injury if you’re in a crash, so let’s buckle up and respect the speed limit.
This story was originally published May 16, 2022 at 5:00 AM.
