Have you ever noticed a heavy-duty pickup truck with a row of semi-truck-style yellow marker lights on its roof? This popular accessory is actually not legal in all fifty states; California lawmakers worry that motorists may confuse yellow markers with police lights. At the same time, pickup trucks are getting wider, and federal law requires several trucks to come with yellow marker lights from the factory. Automakers have come up with a surprising compromise.

Federal law requires that any vehicles wider than 80 inches must have amber-colored “marker” lights. This includes lights on the outside corners of the vehicle and a row of five marker lights placed as high as possible on the vehicle’s roof.

Because most semi trucks and dump trucks are wider than 80 inches, they all come with marker lights. These lights serve two purposes. The lights on the outside corners mark exactly how wide the oncoming vehicle is. The lights on the roof just indicated that an extra wide vehicle is approaching you head-on.

These marker lights are required in all 50 states. Interestingly, the official width of a vehicle does not include mirrors or other accessories or running boards that don’t stick out past the mirrors.

Semi-truck-style marker lights have been a popular aftermarket accessory for pickup trucks, for years. They may make pickup trucks easier to spot on the highway. They also make light-duty pickup trucks look a bit more like heavy-duty semi trucks.

Automakers have begun to offer amber marker lights as a factory-installed option on heavy-duty pickup trucks. General Motors offers a marker light upgrade on its heavy-duty Silverado and Sierra trucks which are equipped with dual rear tires.

There is no clear consensus whether installing semi truck style markers on a regular-width pickup truck is legal. Some folks have speculated that it could be considered “misrepresenting” the width of the vehicle. That said, California is the only state that’s passed a law expressly prohibiting it.

California Vehicle Code 27606 prohibits having a light bar “mounted upon the roof of a vehicle…which emits amber, red, or blue, or any combination of those lights.” According to Pickup Truck Talk, this law aims to keep accessories that may be mistaken for police lights off of civilian vehicles. According to California, such accessories include amber-colored marker lights.

General Motors honors California’s law prohibiting amber marker lights on regular vehicles. If you order a heavy-duty GMC Sierra or Chevrolet Silverado in California, you cannot configure it with amber marker lights.

Several automakers make off-road pickup trucks with wheel spacers that bump their width above 80 inches. These include the Ram 1500 TRX, F-150 Raptor, and Toyota Tundra TRD Pro. All of these trucks come with amber-colored corner marker lights and a row of “top” marker lights set into their grille.

Because these vehicles are wider than 80 inches, the federal government requires they have amber-colored marker lights to warn oncoming motorists. Though these three trucks all have corner lights, their upper lights are mounted lower than normal.

While this in-grille marker light placement may not technically be “as high as possible,” federal regulators have let it slide. Perhaps this is because it honors California’s insistence that automakers and vehicle owners should avoid rooftop lights that might be mistaken for police lights.

Next, see the best pickup truck ladder racks or learn how to install marker lights on your truck in the video below:

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