Interstate 5 spans the West Coast, originating at San Ysidro (San Diego), California, the nation’s busiest international border crossing, and culminating at Blaine, Washington. This freeway connects all of the major population centers of the western seaboard, including San Diego, Los Angeles, Sacramento, Portland and Seattle. Via I-580 and I-505, Interstate 5 provides freeway connections to the populous San Francisco Bay Area.
Guide and Major Projects
Beginning at the International Border at San Ysidro, Interstate 5 connects the metropolitan areas of Tijuana, Baja California, and San Diego, California. Due to significant traffic loads at all hours of the day and night, plans called for expansion of the northbound border inspection facility and realignment of the southbound lanes into a larger border inspection facility. A three phase, $735 million project expanded the port of entry to 62 northbound inspection booths and one dedicated bus lane among other improvements including expanded pedestrian processing facilities and connectivity to a new multi-modal transportation hub in Mexico. Initial work was completed in April 2011 when a new pedestrian bridge was completed. Phase 2, pertaining to the I-5 North and Southbound Inspection Facilities, was scheduled for completion in Summer 2018.3
Passing through the border inspection station, Interstate 5 immediately assumes the role of an urban freeway, with eight to twelve lanes for its entire length through San Diego County. The freeway replaces old U.S. 101, which used to follow surface streets between the border and Downtown San Diego. While some parts of the old road are buried (such as in National City, where it was overrun by the Mile of Cars and in La Jolla, where I-5 was routed on top of the old road), many extant sections of U.S. 101 are still around for driving enjoyment, especially between La Jolla and Oceanside via San Diego County Route S-21.
With the population explosion resonating throughout Southern California, eight lane Interstate 5 is ill-equipped to handle the needs of daily commuters, visitors, business people, international tourists, truckers and more. Plans call for expansion of I-5 in San Diego, for instance, to ten or more lanes, including the implementation of high occupancy vehicle lanes. One such project added an HOV lane per direction from Manchester Avenue to SR 78 during work between late 2015 and 2018. This work preceded the planned construction of I-5 Express Lanes, from La Jolla Village Drive in San Diego to Harbor Drive in Oceanside. These will operate similarly to the I-15 Express Lanes through San Diego County. Work proposed between 2020 and 2035 will upgrade the existing carpool lanes to Express Lanes.
Another large scale project addressing traffic congestion along I-5 was the reconstruction and expansion of the interchange with Interstate 805 through the San Diego communities of Sorrento Valley (Mira Mesa), Torrey Hills and Carmel Valley. The freeway was widened to a dual freeway configuration, which allows for trucks and local traffic to use the lanes that lead to exit ramps, while through traffic may use the express lanes. The northbound local bypass opened in early 2006, followed by the southbound local bypass in Spring 2007.
Continuing north through Orange County, Interstate 5 was reconstructed and widened substantially in the mid-2000s between SR 73 and SR 91. Parts of this section of freeway contain as many as 22 lanes, including auxiliary and carpool lanes. Even so, the interchange between I-5 and Interstate 405 can be very busy and congested during rush hour periods and on weekends.
Entering Los Angeles County, Interstate 5 reverted to its originally constructed alignment, following concrete poured in the 1960s in some areas. I-5 was generally six lanes wide. Construction expanded the freeway northwest from Buena Park to Commerce. Work started between the Coyote Creek over crossing and Marquart Avenue in January 2012. Construction continued on Segment A through December 2018. Segment B between I-605 and I-710 and Segment C at the I-710 interchange was proposed to start in Winter 2025.6
One of the biggest congestion points along Interstate 5 is at the junction with I-10, U.S. 101 and SR 60. This maze of interchanges, ramps and other maneuvers remains largely unchanged since its original construction, and so it is overwhelmed by traffic every day. Through traffic on I-5 is squeezed into two lanes at one point as well as merged with traffic from the busiest freeway in Southern California, Interstate 10 (Santa Monica Freeway). From here, I-5 generally follows old U.S. 99, which was decommissioned in 1964.
Leaving the Los Angeles Basin, Interstate 5 regains its full freeway configuration of eight to ten lanes, but the evening commute generally hits at the north end of San Fernando Valley. The interchange between I-5, I-210 and SR 14 is a choke point, even with the truck bypass. The SR 14/I-5 interchange was also the site of two devastating earthquake collapses, one in 1971’s Sylmar Earthquake and the other in 1994’s Northridge Earthquake.
Beyond San Fernando Valley, Interstate 5 ascends to one of the highest points along its course along the western coast. Crossing the Tehachapi Mountains at Tejon Pass (elevation 4,144 feet) as well as the infamous San Andreas fault, I-5 transitions from an urban to a rural freeway for the first time. In order to make the grade manageable for trucks, the northbound lanes of I-5 just north of Castaic switches sides with the southbound lanes. The result is several miles in which northbound Interstate 5 is on the left side of the freeway rather than the right side. This kind of configuration is uncommon; Interstate 8 east of Yuma, Arizona has a similar inversion of its east and westbound lanes.
Descending into the massive Central Valley via the Grapevine, Interstate 5 immediately splits into two routes: I-5 follows the Westside Highway, avoiding all major population centers between the Grapevine and Tracy. SR 99 follows the old U.S. 99 route, connecting with most major Central Valley cities, including Bakersfield, Fresno, Modesto, and Stockton. Fresno holds the dubious distinction as the largest city in the country not served by an Interstate highway. Nevertheless, Fresno still has its old standby, SR 99. Most traffic destined for the Bay Area and points northward prefer to take Interstate 5, which is shorter and avoids urban traffic.
The next several hundred miles can be peaceful or stressful depending on the day of the week and time of year. During holiday weekends, Interstate 5 can be a parking lot filled with travelers eager to reach relatives and friends in Northern or Southern California. At other times, I-5 is as free flowing as any rural freeway. However, over the past decades, more people have been using “the 5” to connect between Southern and Northern California. As this kind of usage increases, traffic delays become problematic in the Central Valley, even if the nearest city is many miles away.
Once at Interstate 580, travelers en route to the San Francisco Bay Area may exit west to their destination. I-5 remains in the Central Valley, closely following the California Aqueduct and Path 22, the flagship transmission power lines that follow the freeway through much of the state. Whenever Southern California needs power from Northern California, these power lines carry that extra power needed to satisfy their needs. The power lines also work in reverse, thus ensuring that neither part of the state is without power for a long period of time.
Finally I-5 passes through some cities in the Central Valley, including Tracy, Manteca, Stockton, and the capital city, Sacramento. By the time Interstate 5 reaches Sacramento, it has expanded to eight to ten lanes. Passing under Business Loop I-80, I-5 is well below grade … so low that the bottom of the nearby Sacramento River is higher than the level of the freeway as it passes by Old Town Sacramento. Occasionally, with significant amounts of rain and other variables, this section of Interstate 5 may flood.
However, there are plans to change this. Some Sacramento leaders want to see their access to the river restored, and part of that would require removing Interstate 5 from between downtown Sacramento and Old Town Sacramento. I-5 would then be re-routed to the west, connecting with Interstate 80 and Business Loop I-80 in West Sacramento at their current interchange, then continuing northeast to rejoin current I-5 at the current I-5/I-80 interchange. This ambitious plan faces many hurdles, including major cost and environmental concerns, and nothing has been finalized.
Interstate 5 leaves Sacramento almost as quickly as it arrived. Again meeting California State Route 99, I-5 serves the west edge of the northern Central Valley (via old U.S. 99W), while SR 99 and SR 70 serve the east side of the valley (via old U.S. 99E and U.S. 40 Alternate). Most of the towns passed by Interstate 5 are small, but they have seen growth through the addition of fast food restaurants, gas stations and motels. Behind the veneer of these services, old towns with a great deal of history and farming tradition — such as Williams, Arbuckle, Willows, and Orland — await.
Passing through Red Bluff, Interstate 5 enters the rolling hills that separates Red Bluff from Redding. I-5 leaves the Central Valley, and glimpses of towering Mount Shasta become common. Changing from the great valley to mountain scenery, I-5 weaves northward along old U.S. 99. This terrain remains similar as Interstate 5 passes through northern California and enters southern Oregon. By the time it reaches Eugene, the freeway has entered the narrow Willamette Valley, and it approaches Portland.
Both Portland and Seattle have several concerns with Interstate 5. In Portland, the Interstate Bridge over the Columbia River is substandard and causes traffic delays daily. In Seattle, the freeway is congested daily and cannot support the ever increasing crush of traffic.
South of San Diego, Interstate 5 replaced U.S. 101, truncating that route in Los Angeles. However, for the rest of its route northward, I-5 roughly parallels and replaces former U.S. 99, which was decommissioned in stages between 1964 and 1972. Remnants of the old route are now part of California State Route 99, Oregon Route 99, and Washington State Route 99. Although Interstate 5 runs closely to the original route of U.S. 99, large sections of the freeway avoid the old roadway and take on a new alignment, especially between Wheeler Ridge and Manteca. Old U.S. 99 instead passed through Bakersfield, Fresno, and Modesto via modern SR 99, while I-5 stays clear of urban areas until reaching Stockton. In addition, Interstate 5 replaced U.S. 99W between Woodland and Red Bluff. Today Interstate 5 only intersects a handful of U.S. routes, and only three of them are in California (U.S. 101, U.S. 50, and U.S. 97).