States vary somewhat in their laws, but in my home state of California, the laws state only:
California Vehicle Code (CVC) Section 21452(a): "A driver facing a steady circular yellow or yellow arrow signal is, by that signal, warned that the related green movement is ending or that a red indication will be shown immediately thereafter."
CVC Section 21454: "When lane use control signals are placed over individual lanes, those signals shall indicate and apply to drivers of vehicles as follows: (a) Green indication: A driver may travel in any lane over which a green signal is shown. (b) Steady yellow indication: A driver is thereby warned that a lane control change is being made. (c) Steady red indication: A driver shall not enter or travel in any lane over which a red signal is shown. (d) Flashing yellow indication: A driver may use the lane only for the purpose of making a left turn to or from the highway."
A yellow light on a traffic control signal in the state of California only indicates an upcoming transition to a red light, which a driver must stop for. There is no requirement that a driver must stop for a yellow.