Approaching a school bus stop, when should the driver activate the alternating flashing amber warning lights? No federal regulation sets this timing; it comes from the CDL manual and from state law.

Explanation

The amber warning lights go on at least 200 feet, or about 5 to 10 seconds, before the stop, or on whatever schedule the driver's state law sets. The amber lights exist to buy time: they warn following and oncoming traffic that the bus is about to stop before the red lights and the stop signal arm commit it, so drivers behind have room to slow rather than to brake hard beside a group of waiting children. On the federal side the boundary matters here. 49 CFR 383.123(a)(2)(i) names stop signal devices and flashing lights as a required knowledge area, but it expressly qualifies them as devices required for school buses by State or Federal law or regulation, so the paragraph defers to state law rather than setting a procedure, and no federal operating rule prescribes this timing. The federal standard that does address the stop arm, 49 CFR 571.131 (FMVSS No. 131), is a manufacturing specification for the device, not a rule about when a driver switches anything on. Two of the wrong options move the warning to the moment of the stop or after the door is open, which leaves following traffic no advance notice at all and defeats the purpose of having a separate amber stage. The fourth gives a real manual figure attached to the wrong device: 100 to 300 feet, or about 3 to 5 seconds, is when the right turn signal goes on before pulling over.

Source: 49 CFR 383.123(a)(2)(i)