What color lights indicate the crossing of a service road?

The color amber is used to indicate caution and alert drivers to potential hazards or changes in road conditions, making it appropriate for informing drivers about crossing service roads at an airport like O'Hare. Amber lights are commonly used in various traffic control scenarios to signify that a driver should prepare to stop or be aware of nearby pedestrian movement or other vehicles.

In the context of an airport, where safety is paramount, amber lights serve an important function in mitigating risk by signaling to drivers to proceed with caution, reinforcing the need for awareness of their surroundings. This is particularly relevant in service road areas where the likelihood of pedestrians or other vehicles might be higher, thus requiring increased vigilance from drivers.