Why Do Trucks Warn That They Make Wide Right Turns, But Not Wide Left Turns?

After admiring the shiny spikes and plastic arrows on a truck’s tires, you may notice the "wide turns" sign flapping behind them. This warning is usually pasted to a truck’s rear door or hung beneath it, and it comes in bright yellow to catch drivers’ attention. If the signage is detailed, it may caution motorists to look out for wide right turns specifically. The direction a massive semi is turning may seem like an arbitrary safety concern, but these signs highlight the dangers of right turns over left turns for a good reason.

Turning right in an 18-wheel vehicle is an ordeal. It’s dangerous for the same reason that passing a truck on the right is dangerous; any visibility of the vehicle’s right side is limited from the cab. This problem becomes worse when a truck turns right and the convex mirror on that side disappears from view. At least when a truck driver turns left, they can look through their left-side window.

Right turns also require more preparation the bigger the vehicle is. When a truck driver turns left, they have at least half a road’s width to straighten out their trailer. They don't get this wiggle room when making right turns, which is why trucks will swing out to the left immediately before banking right. This maneuver gives the trailer they’re towing space to follow the tractor. It's not an invitation for cars to pass them on the right, especially if the drivers behind the wheel want to keep their vehicles intact.

Semi trucks may look intimidating on the road, but many of their features—from their ornaments to their bumper signs—are designed with safety in mind. Here are more secrets of truck drivers you may not know, and if you’re in search of gifts for truck drivers, check out our gift guide.

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This article was originally published in 2022 and has been updated.