Why Do Semi Trucks Have Yellow Lights on Their Roofs?

Have you ever noticed the five amber-colored lights on the roof of semi trucks? The U.S. government actually requires these lights on all oversized vehicles. But they are not intended to provide extra visibility for the driver, they are actually marker lights to warn other drivers about the size of the oncoming tractor trailer or semi-truck.

Which oversized vehicles need marker lights?

The government requirement for amber-colored marker lights is not based on a vehicle’s height or weight but instead based on its width. Any vehicle 80 inches wide, or wider, must have a set of marker lights.

A tractor trailer driving down a country road at dusk with its amber marker lights glowing.
Semi truck | Josiah Farrow via Unsplash

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Most pickup trucks are just under 80 inches wide for this exact reason. The Ford F-150, for example, is 79.9 inches wide. But when Ford’s Special Vehicle Team (SVT) decided to widen the wheelbase of the F-150 to create the Raptor, it produced an oversized vehicle. For this reason, every F-150 Raptor wears marker lights.

This 80-inch width limit does not include rearview mirrors, flexible accessories such as fender extensions or mudflaps, marker lights, and door handles. You can even mount hard running boards wider than 80 inches on your truck without becoming officially oversized, as long as some feature such as the rearview mirrors is wider than the running boards.

A legal marker light set includes two Front Clearance Lamps at the widest points of the vehicle, often on the outside of its front fenders. It also includes at least three Front Identification Lamps mounted “as high as practicable.” These usually take the form of three or more amber light pods mounted on the roof of the oversized truck.

Why are marker lights mounted on the roof of semi trucks?

The Front Identification Lamps on the roof of a semi truck help other motorists recognize that the oncoming vehicle is an oversized truck. Their high location also makes the truck more visible to the drivers of other semi trucks.

Semi truck | Robson Hatsukami Morgan via Unsplash

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If you just sees a pair of approaching headlights in the opposite lane, it is not always clear what vehicle is behind them. But when you see a pair of headlights below a row of amber marker lights, you know an oversized truck is coming.

But what about when one semi truck encounters another? These trucks’ long hoods create huge blind spots in front of them. Moving at low speeds around a truck stop parking area, it might be difficult for truck drivers to spot the headlights of another truck nearby. In rare instances, installing each truck’s upper markers as high as possible might prevent a fender bender.

Is it illegal for regular-sized pickups to have oversized truck marker lights?

Some folks have pointed out that installing marker lights on a regular truck could conceivably land you a ticket for “misrepresenting the size of your vehicle.” But Jalopnik found no evidence any motorist has ever received such a ticket.

Semi trucks | ay Huang via Unsplash

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In the 1970s and 1980s, the Detroit Three began offering diesel engines in their heavy-duty pickup trucks. These automakers pioneered “big rig” styling to go along with their trucks’ increased towing capacities. One popular option was a set of semi-truck-style amber marking lights on the roof of these pickup trucks.

Today, the oversized Ford F-150 Raptor, Ram 1500 TRX, and Toyota Tundra TRD Pro are inspiring imitations in the same way. Several aftermarket brands are selling in-grille amber LEDs to create a Raptor-like appearance on an otherwise stock truck.

Next, learn why GPS might be getting semi trucks stuck in a mountain pass or see all the lights and reflectors required on a semi truck in the video below:

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