A month ago I moderated an HDT webinar discussing maintenance concerns, and most subjects involved trucks and tractors. But one question sent by a member of our audience had to do with trailers:  

“Why do we still have marker lights on the top of our van trailers? It would save the industry a lot of money and time if we moved them down on the lower rails where a driver could change the light if it was burnt out. When they are up on the top, a driver has to find some way to get up on the top with a ladder or some other means. 

Most tall trailers, like these vans, must have three ID lights at their top-centers. When one's out, someone must climb a tall ladder to fix it. Photo by Jim Park

Most tall trailers, like these vans, must have three ID lights at their top-centers. When one's out, someone must climb a tall ladder to fix it. Photo by Jim Park

“If I remember right, back in the ‘70s they had moved down to the lower rails for about a year or year and a half, and then for some reason went back up to the top. It would be interesting to see how many worker’s comp claims have come from repairing upper marker lights. Those lights are a DOT minimum lighting requirement.”

I posed that question to Brad Van Riper, an active member of the Technology & Maintenance Council and senior vice president and chief technology officer at Truck-Lite Inc., a major lighting manufacturer. His response:

“As you are likely aware, the three marker lamps at the top-rear of the trailer, mounted around the center line of the vehicle, are called ‘identification lights.’ Their purpose is to alert following drivers that the vehicle equipped with these lights is wider than 80 inches. 

The regulations for mounting locations are, in Canada, at the top, and maybe lower if the door header is narrower than 25 milimeters (just under 1 inch), and in the United States, ‘as high as practicable.’

For a period of time in the late 1990s, there was a U.S. interpretation that allowed lower mounting of the lamps, but it has been since clarified to require all lamps be mounted as high as practicable. One case where they are mounted lower is for flatbed trailers that have no high structure; it is allowed to mount them in the rear sill of the trailers. 

With the development of very small LED identification lights, it becomes much easier to locate the lamps in the upper header of most van trailers and most trailers in general. 

One other element of the law is, many times the mounting of lamps is at the discretion of the vehicle OEM, who is responsible for certification of compliance. This certification will be considered correct by the National Highway Traffic Safety Administration (whose Safety Standard 108 governs lighting matters) unless it is ‘clearly erroneous.'”

To comply with the spirit of the law, it would be my recommendation that a trailer be designed so the ID lamps could be mounted on a high level. This would avoid regulatory scrutiny as well as any accident-related product liability issues. 

I am aware of issues that some trailer manufacturers have experienced with new trailers being held up at the border because of lower mounting of lamps, when in the view of the inspector, the lamps could be mounted higher.”

On the move, they're still visible -- and more artsy. Photo by Jim Park

On the move, they're still visible -- and more artsy. Photo by Jim Park

So the short answer is, "It's the law" -- or the reg. Of course, the three red ID lamps are also required on straight trucks and some buses, also to alert motorists that there’s a wide and maybe slow-moving vehicle ahead. Three amber ID lights are required on the front of power units. The high mounting also gives an impression of the vehicle’s height, and thus its overall size.  

Here’s another possible reason: An old-timer once told me that in the days of mostly two-lane highways that pretty much followed the terrain, a truck could crest a hill and only its top would be visible – but not at night if there weren’t those three high-mounted lamps. They’d warn a motorist barreling up from behind that something was there.

Modern Interstates where most big rigs travel today don’t have many of those kinds of hills. But Interstates don’t go everywhere and the old two-laners aren’t totally flattened, so the practice persists because the lights can still be useful. Keep that in mind the next time you have to climb up and change a bulb.

Author

Tom Berg
Tom Berg

Tom Berg

Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational and hybrid vehicles.

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Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational and hybrid vehicles.

View Bio
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