State Route 905 (SR 905) is a state highway in San Diego, California that connects Interstate 5 and Interstate 805 in San Ysidro to the United States – Mexico border at Otay Mesa. The entire highway from I-5 to the International border is a freeway. The highway was formerly routed on a limited-access highway called Otay Mesa Road.

This entire highway is being upgraded to Interstate Highway standards. Once completed, it will become Interstate 905. This route is part of the California Freeway and Expressway System.

SR 905 begins at the intersection of Tocayo Avenue and Oro Vista Road in San Ysidro. It begins as a freeway, intersecting with I-5 and then I-805 after a few exits. Following this, SR 905 veers southeast to parallel Otay Mesa Road, the state route's former alignment, with interchanges at Caliente Avenue, Britannia Boulevard, and La Media Road. The route turns south to its final interchange at Siempre Viva Road. Following this, SR 905 ends at the Mexican border.

The majority of SR 905, running in parallel with Otay Mesa Road from Interstate 5 to SR 125, was added to the state highway system and the California Freeway and Expressway System in 1959 as Legislative Route 281, and became part of State Route 75 in the 1964 renumbering. In 1972, the legislature added a new State Route 117, which extended this part of SR 75 southwest to the Mexican border near Border Field State Park, to the state highway system, and a southerly extension of SR 125 to the border at Otay Mesa to the state highway and Freeway and Expressway systems. SR 117 was extended east to SR 125, replacing this southerly segment of SR 75, in 1976. The Federal Highway Administration approved the continuous roadway via SR 117 and SR 125 from I-5 to the border at Otay Mesa as a non-chargeable (not eligible for federal interstate construction dollars) part of the Interstate Highway System in October 1984, and the number was legislatively changed to 905 in 1986. The original piece of SR 117 (west of I-5), which is not part of the Interstate Highway or California Freeway and Expressway Systems, also became SR 905, but Caltrans has no plans to construct it.[citation needed]

Previously, SR 905 had a direct connection with SR 125 via two at-grade intersections on Otay Mesa Road. With the completion of the newest freeway segment of SR 905 and the freeway-to-freeway connection to SR 125 unconstructed, traffic on SR 905 must exit at La Media Road (exit 7), head north on La Media and head east on Otay Mesa Road to make the connection. A freeway-to-freeway interchange is planned for the connection between SR 125 and SR 905; this interchange will be built when the new SR 11 freeway is constructed. SR 11 will be a toll facility that will serve a new border crossing east of Otay Mesa.

The final freeway segment of SR 905 between I-805 and Britannia Boulevard opened on July 30, 2012.

In February 2008, the multinational construction corporation Skanska announced that it had been awarded a contract by Caltrans to construct a freeway along Route 905 between I-805 and State Route 125:

The project comprises new construction of about 2,5 miles (four kilometers) of six-lane freeway. Construction will require major grading operations for its base and about 103,000 tons of asphalt. The construction contract also covers five bridges, landscaping, storm drains, and an irrigation system, as well as the installation of signal and safety systems.

Once the highway has been fully upgraded to Interstate standards, it will become Interstate 905.[citation needed] Once designated, it will become only the third auxiliary three-digit Interstate to meet an international border (with the other two being Interstate 190 in New York State and Interstate 110 in Texas). I-905 will also be only the second east-west Interstate Highway to connect with a foreign country, joining Interstate 94 which connects with Canada in eastern Michigan.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in San Diego, San Diego County.