So the raindrops noticed a truck, probably a 1 ton or 2 ton, on the way to school yesterday with its clearance lights on and asked why it had all those lights all over it. The best I could come up with is that you often saw larger trucks with those running lights (I didn’t know they were called clearance lights until I did some Googling) on the cab.
Turns out they are called clearance lights, and the DOT requires them on vehicles 80 inches wide or wider. The same regulation that specifies the placement of clearance lights on the tallest part of the cab, also specs reflectors on the sides, the number of reflectors being a product of the length of the vehicle.
This is great, all kinds of ignorance fought. But…I couldn’t find any explanation of WHY they are required. I found lots of places where people were asking WHY, and lots of speculation, but nothing definitive. I guess the easiest answer is visibility, and since they are called clearance lights and have to go on the highest point that they help determine if a large vehicle will clear a low hanging obstruction. But the reflectors specified by number on the front sides seems to hint at more. Anyone know the why? Or is it just the obvious and the codification into law makes it seem like there is more to the story.
-rainy
It’s so oncoming traffic can tell a larger wider vehicle is coming their way at night so they can provide proper clearance. It’s important on narrow roads.
Aside note is all the 3/4 and 1 ton pick ups manufactured in the US are made to fall within the inch limitation, so do not require clearance lights. Most dealerships order them with clearance lights because most the clientele will be using them to tow trailers wider than 80 inches, which would require the lighting. If an officer wants to be a jerk they can ticket vehicles towing wide trailers, like campers without proper clearance lights.
I believe the DOT requirement is 4 lights but most models of pick-ups use 5. I don’t know if one of the states requires 5.
They’re also important for crossing traffic. In the dark you might not know how long a tractor-trailer rig is and could run into the back of it instead of waiting for it to completely cross. That’s mainly for lights along the length of the rig, rather than in the front.
But the 80" wide and GVW criteria are mainly to distinguish the commercial vehicles from the non-commercial, and big pickups get swept up in the mix.
That makes sense, except surely with a trailer wider than the truck, it’s the trailer that most needs the lights? The lights on the truck are much less relevant in that situation.
I saw a truck with this lighting, including along the top of the trailer, last week, and I thought it was there as a sort of holiday decoration. It does make the outline of the truck very visible, so it sounds like a good idea.
A 1 ton pickup with single rear wheels isn’t required to have the clearance lights. The same truck with dual rear wheels is required to have clearance lights.
Some drivers like to make their trucks look pretty and light them up like a Coca Cola advert. In the UK, apart from the normal side/headlights, lights are required on all the corners of a truck/trailer and at intervals down each side. This makes it much easier to see the size of a vehicle in the dark.
<joke> The lights fail on a car transporter so the driver switches on the lights of the top front car and drives on those. After a few miles, a car coming the other way suddenly swerves into the ditch on his side of the road. The transporter driver stops and runs back to the ditched car. “What happened,” he asks.
The shaken car driver says, “I saw the lights coming towards me and I suddenly thought - if it’s that high how ******* wide is it?”
In Japan large trucks have three lights on the top of the cab but they are green, not yellow. The faster the truck is going the more lights are supposed to be lit but on Okinawa, at least, they rarely worked well.
The Ford Raptor, for example, can exceed 80” width. Its clearance lights are on the grill. The regulation doesn’t specify “on top of the truck”; they only specify “as high as practicable.”
On my FIL’s 1 ton dually Ford, the only clearance lights are a small red light on each fender extension over the outboard rear tires.