DENVER (AP) — Colorado's transportation agency began using a driverless truck on Friday that is designed to protect highway work crews from oncoming traffic.

The truck is officially known as an Autonomous Impact Protection Vehicle, but it is not really autonomous like the self-driving cars being tested around the country. Instead, the truck is electronically controlled by a driver in another truck ahead of it.

If the protection vehicle loses its electronic "tether" to the lead vehicle, it is programmed to pull over and stop.

Like other trucks that follow highway crews and display messages or a...