Most are two-lane highways, and can accommodate high speeds and large volumes of traffic.

Routes in Lake and San Bernardino Counties are designated by numbers only.

In San Diego County, reassurance markers are placed as frequently as they would be on state highways.

For most county routes, signage may be found at the beginning and end and at major junctions; reassurance markers are rare and are placed at distant intervals.

The county routes are alphabetically sorted by the prefix letter in its shield, followed by the corresponding number.