Q: I’m very concerned about the people on the roads who never seem to use their high beams. Out in the county there can be literally anything on the road and high beams are needed to see what is there. Can you give the stopping distance for a car traveling at, say 50 mph, for the average driver? And how far does the average low beam travel? We had one neighbor who said she never used her high beams “because the lights frighten the deer and cause them to run into the road.” Honestly. Have you ever heard this argument? Can you please rebut it for me? She won’t listen to us. Are there any laws for drivers who aren’t using high beam when needed?
A: I’ve heard plenty of criticism of drivers who fail to dim their headlights; this is the first time someone has written in with such passion demanding that drivers use their high beams more often. And it is a valid point. I think as drivers we often overestimate the effectiveness of our headlights and think we can see farther than we really can. So let’s work through the questions.
What is the stopping distance at 50 mph? We’ll work with averages here. Road surface, weather conditions, tire tread and brake pads all factor in to stopping distance. It typically takes a driver about three-fourths of a second to recognize a hazard and another three-fourths of a second for the brain to tell the body to put the foot on the brake and have the foot actually start pressing the pedal, giving us a reaction time of 1.5 seconds. A driver can safely decelerate a vehicle at about 15 to 20 feet per second (fps). Let’s assume a best case scenario of 20 fps. At 50 mph (or a bit over 73 fps) a driver travels 110 feet in the 1.5 seconds it takes to react and another 133 feet to bring the car to a stop, for a total of 243 feet.
How far does the average low beam travel? By law, a low beam is required to “reveal persons and vehicles” at a distance of 150 feet. Real world examples are somewhere around 160 to 180 feet. If you do the math, that puts our visibility in a best case scenario at over 60 feet short of what we need based on the stopping distance above. (And still traveling at roughly 30 mph.) To reiterate, these numbers are a best case scenario; an alert and skilled driver on a dry road surface in a well-maintained vehicle with properly adjusted headlights. Your own results could easily be worse, but not likely better. Based on the math, driving within the limits of low beams requires speeds below 35 mph. Also, you didn’t ask, but high beams are required to illuminate to a distance of 450 feet.
Do high beams frighten deer? I’m no deer expert, so I reviewed the wisdom of people who really know deer; mostly hunters, zoologists and insurance companies. (They deal with a lot of car/deer collisions, over a million a year.) It’s pretty unanimous; deer are wildly unpredictable. Who knows what a deer will do, no matter what setting your headlights are on. The deer experts also agreed that high beams are the best bet because your only real hope of avoiding a deer is to see it as early as possible so you have time to slow down.
Have you ever heard this argument? No, not until you asked, but in researching your question I came across what might be the dumbest strategy to avoid hitting a deer at night. There is a person (on the internet, of course) who is convinced that headlights cause deer to panic and the best solution is to drive with headlights off in deer country.
Are there any laws for drivers who aren’t using high beams when needed? We all know (at least I hope we know) the law requiring drivers to dim high beams for other traffic. That same law also includes a requirement that drivers use light of a “sufficient intensity to reveal persons and vehicles at a safe distance in advance of the vehicle . . .” That doesn’t specifically require the use of high beams, but it would be reasonable to conclude that if you’re driving faster than your low beams can illuminate (again, less than 35 mph) high beams would be required.