Friday, February 13, 2009


Driving in the dark tonight, I was reminded of a problem that has bothered me for years. Hang with me here for a bit, hopefully it will become clear.

When you are in your car or pickup, your eyes and the headlights on your vehicle are at about the same level. The eyes are actually a foot or two above the headlights, but for this exercise, they are close enough to consider them the same height.

Now look at a large truck. A conventional cab has the headlights at about the level of the driver's feet. A cabover is even higher. They have to be that low so that smaller vehicles aren't blinded - think a light bar on an off road truck. The driver also sits in a more vertical position than in a car - car drivers generally have the feet stretched out and the seat back leaning rearward - similar to a recliner. A truck seat is more comparable to a kitchen chair. This is because most truck seats have air suspensions, and not many human backs could take the pounding a reclining position would cause. So, the driver's eyes are more towards the upper reaches of the cab - as is the automobile driver, but there is less of a gross difference than a large truck.

So, at night, when you meet a truck and see the marker lights on top of the cab - the driver's eyes are just underneath those lights. Your eyes are closer to the level of your headlights.

This is an issue when you meet a truck cresting a hill and the auto still has it's bright headlights on. The driver of the car cannot see the headlights of the truck, so most just leave their brights on until they get a line of sight on the truck headlights. Meanwhile, the trucker is being blinded by those bright lights. Remember, when you are in your car and can see the cab marker lights, the driver sees you and your vehicle as well.

As far as I know, this isn't something taught in driver's ed classes nor is it taught in any truck driving school I've ever heard of. I don't think a lot of truckers have figured this out, considering the complaints I hear at night about "that damn four wheeler didn't dim it's light until I was almost on top of it." Well, while there are plenty of people who don't dim their lights properly, some don't simply because it never occurred to them that maybe they should "dim" even though they cannot see the oncoming truck's headlights.

Now, there are those out there that just won't give a damn one way or the other, so I hasten to remind them that they might be meeting a drug crazed slack jawed mouth breather whose whole life has gone badly and he just needs one more thing to push him over the edge. He's driving a forty ton vehicle in your direction, and he might just be ready to take action.

But, odds are it's someone like me who has put in a long day and whose irises don't contract as fast as they used to back in the day, so y'all will be blinding the tired tubby trucker who is resigned to having one more light bloom staying in his vision for the next few minutes, and hoping it doesn't cover a deer or some other hazard that he'd sure like to see a bit better.


Mo K said...

That's "good to know" kind of stuff! Thanks!

Farm.Dad said...

Good post . I will also point out that one of my flirtations wayy back in the day was a career as a truckdriver , and from that i consider it common courtesy ( assuming a wide enough " safety lane " ) to pull over on the downhill side when a semi is overtaking me and allow him around irrespective of traffic . Many will wait till the uphill side( passing lane or no )after he has lost all the momentum . I guess it is just a hat tip to my past of driving " short legged " and heavily loaded trucks while being paid by the mile . Used to be i would see a " thank you " blink of the trailer lights when i did this , but nowadays that has become rare . I guess " Truk Drivin Skewl " is a mixed blessing lol .

Anonymous said...

I actually learned this decades ago in a defensive driving class my dad made me attend -- it was taught by a police officer who used to be a trucker.

I will admit that I now have automatic dimmers in my vehicle, and when I have had a long day, will turn them on so as not to forget to dim my lights.