Highway Notes and Glossary

With all the highways and byways here in Southern California, there are some bits of information that aren’t as easy to categorize. This page will contain those tidbits of information in one easy place. It will also contain definitions for some of the terms used on this site. This will not be a static page, so check back for updates.



Zero Mileage Points:

Traveling around the region, you see many directional signs pointing toward Los Angeles and San Diego. Sometimes those signs will be within those same cities, so why keep pointing there? Well, both of those cities have a central point and that is where the signs and mileage are referring.

For Los Angeles, the control point is the Four Level Interchange, where US 101 and State 110 cross. All Los Angeles mileage goes to zero at that interchange. Prior to its construction in 1949, the control point was the intersection of 7th St and Broadway.

For San Diego, the story is similar. The zero point and location where the control point is the “Other Four Level Interchange”, the I-5 and State 163 interchange. Prior to its construction, the control point was Horton Plaza at the intersection of 3rd Ave and Broadway.

Freeway Facts (To be expanded to cover San Diego and Imperial Counties):

Freeway NameRoute NumberYear BeganYear Completed
Antelope ValleySR-1419631972
Arroyo Seco ParkwaySR-11019391953
Corona (Chino Valley)SR-7119711998
Costa Mesa (Newport)SR-5519621993
FoothillI-210, SR-21019552007
Garden GroveSR-2219591967
Glenn Anderson (Century)I-10519871993
Golden StateI-519541968
HarborSR-110, I-11019511962
HollywoodUS 101, SR-17019401966
Long BeachI-71019521975
Redondo BeachSR-9119851985
Richard M NixonSR-9019621962
Ronald Reagan (Simi Valley)SR-11819681993
San BernardinoI-10, I-21519441957
San DiegoI-405, I-519571969
San Gabriel RiverI-60519631971
Santa AnaI-5, US 10119441958
Santa MonicaI-1019611964
Terminal IslandSR-47, SR-10319471947
VenturaUS 101, SR-13419531972

Highest Points:

  1. Onyx Summit at 8443′ (SR-38) – San Bernardino Co
  2. Dawson Saddle at 7901′ (SR-2) – Los Angeles Co.

Highest Connector Ramp:

  • 130′ (I-105 HOV East or West to I-110 North HOV)

Highest AADT:

  • Santa Ana Freeway at the Orange Crush Interchange – Jct 5/57/22 (410,000 in 2015)

Lowest AADT:

  • State 173 along unpaved portion (20)

Most Lanes (including HOV):

  • 12 (Santa Ana Freeway in Orange County)

Most Lanes at an interchange:

  • 24 (I-5/I-405 South at the El Toro Y)

Most Levels to an interchange:

  • 5 (I-105 / I-110)

Shortest Freeway:

  • Marina Freeway (SR-90) at 2.25 miles

Most Routes Intersecting:

  • East Los Angeles Interchange Complex (I-5, I-10, SR-60, US 101)

Most Named Routes Intersecting:

  • East Los Angeles Interchange Complex (Santa Ana, Santa Monica, Pomona, Golden State, San Bernardino)

Most Common Local interchange type:

  • Diamond and Two Quadrant Clover

Oldest Freeway:

  • Arroyo Seco Parkway (1939-1940)

Newest Freeway:

  • Foothill Freeway Extension (2007)


Average Annual Daily Traffic (AADT) from Caltrans – Annual average daily traffic is the total traffic volume for the year divided by 365 days. The traffic count year is from October 1st through September 30th. Very few locations in California are actually counted continuously. Traffic counting is generally performed by electronic counting instruments moved from location to location throughout the State in a program of continuous traffic count sampling. The resulting counts are adjusted to an estimate of annual average daily traffic by compensating for seasonal influence, weekly variation and other variables which may be present. Annual ADT is necessary for presenting a statewide picture of traffic flow, evaluating traffic trends, computing accident rates, planning and designing highways and other purposes.

Control City or Point – A location that highway signs and mileage end at. An example sign would read:

Newhall             15
Santa Paula     40
Ojai                      95

Shown here, Los Angeles is the control city.

Ojai would be the “Control City” in this sign. At or near Ojai, the next distant city would be displayed. Sometimes that city is on another highway or it isn’t a city at all, such as giving US 101 as an end point. The point is give travelers an idea where the road is generally going. Signage on I-5 heading northbound from Los Angeles gives Sacramento as a control city, being the next major city it passes through. It was formerly signed as Bakersfield, which was the control city for US 99.

HOT Lanes  or HO/T Lanes – used to describe lanes on a freeway which are normally HOV lanes but SOV (Single Occupancy Vehicles) can purchase a transponder to drive in the lanes themselves. These lanes are becoming more commonplace as funding for HOV only lanes is becoming more scarce. HOV traffic, however, is still generally free. It varies by facility (or agency) whether or not a transponder is required for all vehicles. For information about these agencies, go to this page.

High Occupancy Vehicle (HOV) used to describe vehicle carrying more than one person. HOV lanes were formerly called Carpool Lanes or Diamond Lanes. Motorcycles are generally the exception where they can ride in HOV lanes with just one person.

Signage for the 55 North HOV connection

Single Occupancy Vehicle (SOV) – Used to identify any vehicle that is carrying only one person regardless of actual capacity and to differentiate from HOV.

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