Route 15 is defined as follows in section 315 of the
California Streets and Highways Code: Route 15 is from: (a)
Route 5 in
San Diego to
Route 8.(b) Route 8 to the
Nevada state line near
Stateline, Nevada via the vicinity of
Temecula,
Corona,
Ontario,
Victorville, and
Barstow. The section of Route 15 defined in subdivision (a) is not considered an Interstate Highway according to the
Federal Highway Administration (FHWA)'s route logs. and are part of the
National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the
Federal Highway Administration. I-15 from
SR 76 to
SR 91 and
SR 58 to
SR 127 is eligible to be included in the
State Scenic Highway System, but it is not officially designated as a scenic highway by the
California Department of Transportation.
San Diego County SR 15 begins south of
I-5 at 32nd Street near Harbor Drive. After this, SR 15 has an interchange with
SR 94, The route then meets
I-805; however, one can only continue in the same direction that they were going at this interchange, since the overall shape of this interchange is an elongated "X". Between the Polk Avenue and Orange Avenue overpasses, the freeway goes under a city park that was built on top of the freeway during construction in 2001. Pedestrian bridges were also built at Monroe Avenue and Landis Street to reduce the effects of the freeway geographically dividing the community. Between
I-805 and
I-8, SR 15 follows the former alignment of 40th Street, which was its former routing as a city street. It continues seamlessly into the southern terminus of I-15 at I-8; on the northbound conversion to I-15 at I-8, there is no "End SR 15" sign. There are various local names for the highway, such as the
Escondido Freeway between San Diego and Escondido. I-15 between
SR 163 and Pomerado Road / Miramar Road is known as the
Semper Fi Highway in recognition of the nearby
Marine Corps Air Station Miramar. I-15 runs along the eastern edge of the
Santa Ana Mountains, passing through the cities of
Wildomar and
Lake Elsinore. In Lake Elsinore, I-15 intersects
SR 74, a major highway connecting the city with
San Juan Capistrano as well as points east such as
Perris,
Hemet,
Idyllwild, and the
Coachella Valley. It continues northwest through the unincorporated area of
Temescal Valley as the
Corona Freeway and passes through the city of
Corona. During this stretch, I-15 has an interchange with SR 91, a major east–west highway; this interchange serves as a vital link between southwestern Riverside County and Orange County. North of SR 91, I-15 continues through the city of
Norco, crosses the
Santa Ana River, and heads due north along the boundary between the cities of
Eastvale and
Jurupa Valley. I-15 enters San Bernardino County just past an interchange with SR 60, another major east–west highway, which connects I-15 with the
Chino Valley and the southern
San Gabriel Valley. I-15 passes through the city of
Ontario on its way to
I-10, the main east–west artery though Southern California. North of I-10, I-15 passes through the cities of
Rancho Cucamonga and
Fontana as it intersects
SR 210, an east–west highway skirting the
San Gabriel and
San Bernardino mountain ranges. SR 210 connects I-15 to major foothill communities such as
Pasadena,
Rialto, and
San Bernardino. I-15 also crosses old
US 66 during this stretch of highway, which is signed as
SR 66, Foothill Boulevard. At this junction, I-15 takes a strongly northeastern alignment as it moves to rejoin with its spur route, I-215, in
Devore, in northern
San Bernardino. The highway then heads northward and upward through the
Cajon Pass, an important mountain pass that is the primary route between Southern California and points further north and east. The portion of I-15 that is located between its northern and southern junctions with I-215 is also used by many local residents as the major north–south route for the western portions of the San Bernardino–Riverside–Ontario metropolitan area. (I-215 serves a similar function in the eastern portion of the metropolitan area. These two highways are also the only continuous north–south freeways in the area.) North of Limonite Avenue (south of SR 60), I-15 is known as the
Ontario Freeway (formerly known as the
Devore Freeway prior to 1989). After its northern merge with I-215 in Devore, I-15 is called the
Barstow Freeway or the
Mojave Freeway. A short section between
SR 138 and Oak Hill Road is also designated as the '''CHP Officer Larry L. Wetterling and San Bernardino County Sheriff's Lieutenant Alfred E. Stewart Memorial Highway''', named after two officers killed in the line of duty. On this stretch of highway, I-15 northbound splits from I-15 southbound, where the road ascends up a steep grade until it reaches Cajon Summit (elevation ) just south of the High Desert communities of Hesperia and Oak Hills. Tractor-trailer trucks headed southbound are required to travel at the posted speed limit of or less due to the steep downward grade. The southbound lanes provide a
runaway truck ramp as a safety feature. The two halves of the highway rejoin shortly before reaching Cajon Summit. North of the Cajon Pass, I-15 traverses the
High Desert cities of
Hesperia, where it meets the southern end of
US 395, and
Victorville. I-15 passes through desert for before reaching
Barstow, where it meets the eastern terminus of
SR 58 and the western terminus of
I-40. It then passes
Zzyzx Road more than later, before reaching the town of
Baker. The sign for Zzyzx Road—alphabetically the last place name in the world—is a landmark of sorts on the drive between Los Angeles and Las Vegas. Northeast of Baker, I-15 passes through the Halloran Summit near
Halloran Springs at an elevation of over , then descends into the
Shadow Valley before ascending again through the
Mountain Pass at an elevation of . A runaway truck ramp is provided for northbound I-15 traffic near the
dry Ivanpah Lake at the end of Mountain Pass. I-15 then crosses the Nevada state line at the casino town of
Primm, Nevada, southwest of
Las Vegas. The Mojave Freeway is fairly busy on weekdays, since it connects the rapidly growing
exurbs of the Victor Valley with the Los Angeles area. On weekends and holidays, however, it can sometimes be jammed with Californians driving to Las Vegas for short vacations.
Express lanes . Note the variable fees for the minimum toll, and for the rates to travel to either SR 56 or SR 163. There are two sections of
high-occupancy toll (HOT) lanes along I-15. The first section is in San Diego County between SR 163 in San Diego and SR 78 in Escondido. The lanes were originally constructed as reversible carpool lanes in 1988 before they were converted into express lanes a decade later. Between 2004 and 2008, construction extended the lanes north from SR 56 to Del Lago Boulevard in Escondido. Then, between 2009 and 2012, work was done to widen the southern reversible segment from two lanes to four, and then extend the corridor north to SR 78. The lanes, dubbed a "highway within a highway", include a movable "zipper" barrier for , which can be changed to create an extra lane as demand allows. In addition, five direct access ramps allow for easier local access, as well as access to bus service from
MTS Rapid. These express lanes carry the hidden state highway designation of
Route 15S (for "supplemental"). The second segment of HOT lanes is in Riverside County, featuring one to two tolled express lanes in each direction from Cajalco Road in Corona to Cantu-Galleano Ranch Road near SR 60 at the Eastvale–Jurupa Valley line. These lanes began construction in 2018 and opened in 2021. , some toll policies differ between the counties. The HOT lanes in San Diego County are simply branded as the "I-15 Express Lanes" and are administered by the
San Diego Association of Governments (SANDAG). For the segment in San Diego County, each solo driver is required to carry a FasTrak transponder, while carpools and motorcycles are not charged. SANDAG does not use or offer the switchable FasTrak Flex tags directly, and instead instructs those drivers who do qualify for free to just remove their FasTrak tag off their windshield or cover it in the provided mylar bag to avoid being charged. There are long-range plans to extend the Riverside County segment at least as far south as SR 74 (Central Avenue) in Lake Elsinore. A separate project would extend the express lanes from Cantu-Galleano Ranch Road into San Bernardino County as far north as Duncan Canyon Road in Fontana. Phase 1 of the San Bernardino County extension started construction in March 2025 up to just north of Foothill Boulevard. ==History==