How do vehicles of the Department of Transportation indicate warnings?

The correct response indicating how vehicles of the Department of Transportation provide warnings is amber. Amber is a color that is universally recognized as a cautionary alert, especially in traffic and vehicle contexts. Vehicles equipped with amber lights signal to other road users that they are either working or present in a construction or maintenance zone, thereby enhancing safety for both the workers and the public. This standardization of color helps ensure that people can quickly and easily understand the intent behind the vehicle's presence.

Other colors such as red are more associated with emergency vehicles, which may not apply in this context. Blue can indicate law enforcement presence, while white and clear lights are typically used for illumination or visibility rather than signaling warning or caution. Hence, amber is specifically chosen for its effectiveness in communicating warnings on Department of Transportation vehicles.