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General Knowledge · Seeing

Why must a bus, truck, or truck tractor be equipped with two rear-vision mirrors, one on each side?

1.Federal equipment regulation requires them so the driver has a view of the highway to the rear and along both sides, since most large commercial vehicles have no usable rear window viewCorrect answer
2.It is only needed to pass a state vehicle registration and safety inspection conducted once a year, and is not an everyday federal driving requirement of any kind
3.It is required only for vehicles that are currently carrying fare-paying passengers for hire along a regularly scheduled intercity bus route today only
4.Mirrors are recommended by vehicle manufacturers as a helpful safety option, but they are not actually required anywhere under federal law or regulation

Explanation

Federal equipment regulation requires every bus, truck, and truck tractor to be equipped with two rear-vision mirrors, one at each side, giving the driver a view of the highway to the rear and along both sides of the vehicle, under 49 CFR 393.80. This exists because most large commercial vehicles have no usable rear window view, making mirrors the only way a driver can see traffic behind and beside the vehicle. Unlike the shifting and basic-control facts in earlier topics, this is a genuine federal equipment mandate, not a state inspection formality, and it is not limited to passenger-carrying vehicles. It is also not merely a manufacturer recommendation; the regulation itself requires it, using mandatory language.

Source: 49 CFR 393.80

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