Interstate 15 is connected to parts of State Route 15 and Route 15 and it happens to be a major state highway within California which connected San Diego, San Bernardino and Riverside Counties. This route is almost 288 miles long and Interstate 15 happens to extend through the Canada-US Border, Montana, Idaho, Utah, Arizona, and Nevada as part of a major interstate highway. This interstate is also a major thoroughfare for a lot of traffic that travels between Las Vegas, Nevada and Southern California as well as between Inland Empire and San Diego, and some points beyond that.
Just south of the junction located near Interstate 8 within San Diego, the highway will become State Route 15 and it will extend about 6 miles to Interstate 5 for about 12 miles to the Mexican Border. This small segment was initially meant to be a state route instead of an interstate, but because of the recent interstate standards, it is being upgraded to become part of Interstate 15 in the future. Included within this part of the highway, the whole length is called Route 15 which stretches about 294 miles into California.
Interstate 15 has plenty of areas that are designated as the Mojave Freeway, Barstow Freeway, Ontario Freeway, Temecula Valley Freeway, Avocado Highway, and the Escondido Freeway. It also has portions that are considered to be part of a memorial highway for CHP Officer Larry Wetterling and Sheriff Lieutenant Alfred Stewart.
However, over the years Interstate 15 has replaced US 66 that was between Barstow and San Bernardino, as well as US 91 which ran north of Barstow and it also replaced US 395 that ran between Temecula and San Diego.
Interstate 15 was originally planned to run from Interstate 10 which is in San Bernardino and run along the Interstate 215 alignment then up to Cajon Pass and through to Las Vegas, Nevada being a distance of 187 miles within the state. However, California had argued successfully that the addition that is south of San Diego would be useful to connect major military bases such as MCAS Miramar and March ARB.
It would be during 1957 when the State Highway Commission would state that the Escondido Freeway to be Routes 215 and 15 from Route 91 and 805. This whole part was originally US Route 395 whenever it was first named. It has been since then that it was extended to Route 15 south to Route 8 during 1979. Then in 1990, Route 15 from San Diego County would become the I-15/I-215 interchange and was called the Temecula Valley Freeway.
The present-day State Route 15 was signed into effect after the creation of Interstate 15 during 1968. The terminus for Interstate 15 was at Interstate 8 and State Route 15 was mostly considered to be along Wabash Boulevard and 40th Street within San Diego would eventually merge into Interstate 5. The area that is between Interstate 805 and Adams Avenue has remained to be a city street for a long time and this area was completed until after January of 2000. It is for this reason that this freeway is called the 40th street freeway.
To learn more about Interstate 15, Check out: http://www.cahighways.org/009-016.html#015 .