Three-Lane Highways
There are two types of three-lane highways.
The first kind of three-lane highway designates one lane of traffic for each direction and a middle lane for vehicles making left turns or passing. Unless specified, the middle lane is not used for regular through traffic.
Speed Limits for Authorized Vehicles
22406. Driving any of the following vehicles faster than 55 miles per hour on a highway is strictly prohibited.
(a) A truck or tractor trailer equipped with 3 or more axles or a truck or tractor trailer hauling another vehicle of any kind.
(b) A bus or any passenger vehicle hauling another vehicle of any kind.
(c) A school bus occupied by one or more students.
(d) Any farm-related vehicle while carrying passengers.
(e) All vehicles shipping explosives.
(f) Any bus trailers (Please refer to Section 636).
Sec. 22406 vehicles should always drive in designated lanes. If no lane has been designated, these vehicles should use the right-hand lane or drive as close as is practical to the right-hand edge or curb. If a divided highway has at least four lanes of traffic moving in the same direction but has no designated lanes for these types of slow-moving vehicles, then they are permitted to drive either in the right-hand lane or in the lane immediately to the left of the right-hand lane (that is, the lane second from the right).
Exceptions:
Sec. 22406: vehicles may drive in a different lane if they are doing any of the following:
Preparing to turn left or right
Preparing to exit the highway
Passing an even slower vehicle
Being forced to drive in a lane other than the right-hand lane in order to continue along the intended route.
Special “Turnout Areas”
On two-lane roads, there are sometimes special marked "turnout" areas. The purpose of a turnout area is to allow vehicles behind you to pass. When driving slowly on a two-lane road where passing is unsafe, and five or more vehicles are following you, utilize the first designated turnout to move off the road safely, thus allowing the vehicles behind you to pass. This applies even to passenger vehicles.
Some two-lane roads have "passing lanes" provided at wider sections of roadway.