Which is a signal for a towing vehicle to proceed?

A steady green light is universally recognized as a signal to proceed. In traffic control, green typically indicates that it is safe to move forward. For towing vehicles at O'Hare Airport, this signal would mean that the vehicle is allowed to continue its journey without stopping, following the established traffic rules in the area.

In contrast, other signals imply caution or the need to stop. A hand wave might indicate to a driver to proceed but is often reliant on the context and the person signaling, making it less standardized compared to traffic lights. A blinking yellow light generally alerts drivers to exercise caution and be prepared to stop, while a red flashing light unequivocally commands that the vehicle must stop. Thus, the steady green light is the only signal that clearly provides the directive for a towing vehicle to move forward safely.