US Route 466 Daughter Road Tribute Page: An Explanation of the California Highway System

In California there are basically four different kinds of highways:
Interstate highways--abbreviated I-XX
US highways--abbreviated US XX
State highways--abbreviated SR--XX
County roads--abbreviated CR--XX

Interstate Highways

The Interstate System was developed as a Congressional act in 1956. Putting it simply, its a system of escape routes to use in the case of imminent danger. The term "Interstate" is a little misleading... The roads don't necessarily connect one state with another. There are Interstate highways planned for every jurisdiction of the United States. It has very simple numbering...
PRIMARY--One or two digits. Generally odd numbers go north and south. Even numbers go east and west. The north-south Interstates start small in the south and gradually get larger going north. The east-west Interstates start small in the west and gradually get larger going east. Presently, the westernmost Interstate in the continental U.S. is I-5. The easternmost is I-97. There is an I-99 that is out of order (and a few other numbers too), but they all conform to the standards. The southernmost Interstate in the continental U.S. is I-4. The northernmost is I-96. There is room for more numbers.
SECONDARY--Three digits. Odd numbers are spurs. They go in but they don't come back. They may even connect one Interstate with another. Example: I-505 in California is a "jug handle" spur connecting I-5 to I-80, diverting traffic from Sacramento. Even numbers are bypasses or loops. The go around and come back to the primary. The second two digits denote the primary Interstate. Example: I-405 in California is a bypass of I-5 that goes around the middle of Los Angeles. There are exceptions to these rules: One of the shortest Interstates is I-238 in California. There is no I-38. It's a spur/connector, not a loop or bypass. The number is an extension of SR-238. Caltrans (California Department of Transportation) has its own rules on numbering and the numbers 180, 380, 580, 780, and 980 had all been used. The U.S. Department of Transportation (DOT) would not allow an I-1180, so the state highway was extended.
BUSINESS LOOP: A road of any kind which goes around an Interstate highway. Signage is green.
BUSINESS SPUR: A road of any kind which connects an Interstate highway with a particular point with no point of return, except to turn around. Signage is green.

US Highways

At one time this was known as the US Interstate Numbering System. When the Interstate Defense Highway System started the Interstate part was dropped. And like the newer Interstate highways, the older system wasn't necessarily a system of roads that went from state to state. It only covered the 48 conterminous states. Remember that Alaska and Hawaii weren't states yet. These roads were not and are not Federally funded. They are different in different states. There are rules set up by the American Association of State Highway and Transportation Officials (AASHTO), which are often ignored.

Here is a fairly simple explanation of how the numbers work:
PRIMARY ROADS: One or two digits. East-west routes are even. North-south routes are odd. They start small in the east and the north and gradually get larger in the west and the south. Supposedly, they ran out of numbers and after US 99 they needed one more north-south highway, so US 101 was charted. It has no secondary roads connected with it. There are a couple of other primary roads with three digits which absolutely no logical reason for existence: US 400 and US 412.
SECONDARY ROADS: Three digits. They can generally do whatever their respective jurisdictional highway authorities want them to do and go almost anywhere. For the most part, they were all spurs of one kind or another. No formula here. And the "daughter roads" didn't necessarily meet their "mother roads" at any point. Take US 395: Nowhere does it even come near to US 95. Anymore discussion would just add confusion.
BANNERED ROADS: These are roads which work from the main road.
-BYPASS: It goes around. Sometimes the main route is marked "Bypass," which is a freeway. The former surface street route is marked "Business."
-BUSINESS: It goes through (and allows for large commercial vehicles).
-CITY: It goes through (and does not allow for large commercial vehicles).
-SCENIC: Usually a narrow road with a slow speed limit to see something the highway people think is pretty.
-SPUR: It goes somewhere but it doesn't come back.
-ALTERNATE: Gives a second opinion as to where you are going.
-TRUCK: A bypass route with enough space for large commercial vehicles.

State Highways

MAIN ROADS: The numbering varies. Signage is green.
BANNERED ROUTES: Roads that work from the main road:
-BUSINESS: Usually the old highway.
-TEMPORARY: This is now the route since the main route is under construction.
-AUXILIARY ROUTES: Shown by letters that follow the numbers.
--S: Supplemental
--U: Unrelinquished (the state considers this the main highway, even though a freeway goes around it)

County Roads

Most county roads in California are surface streets. San Diego County probably has the most extensive system. It had the green mileage numbers long before the Interstates had them. (Remember, California didn't even get those until about 2008!)

As far as the numbering goes, most have a letter followed by one or two numerical digits. This is the state system other counties have their own way of doing things with their own signs. I used to think these blue and gold shields were only found in California (state colors, you know) but they are fairly standard in other states.

California Peculiarities

Before California had green mileage markers like the other states, it had these Postmile signs. The three digits at the top are the number of the highway (this is I-10). Next is the county: This is Riverside County. Then there was the location. Miles would be counted from west to east and south to north but their occurrence was not uniformed. Which is why certain isolated parts of the state would have speedometer odometer checks: signs stating MILE 1, MILE 2, MILE 3, and so forth. With the green mileage signs, the odometer checks are not necessary. The miles were counted from county line to county line, then start over again.

You don't see signs like this in California. The state only has six US highways (6, 50, 95, 97, 101, and 395). So a little extra care is given to signage.

Types of Superhighways in California

Freeway: Control access highway which is paid for with taxes.

Toll Road: Control access highway which is privately funded (aided by motorists' tolls) but patrolled by public law enforcement personnel. California makes a distinction between freeways and toll roads.