The western leg of State Route 138 traverses the Lancaster Freeway from Interstate 5 to Gorman Post Road, Lancaster Road from Gorman Post Road to 245th Street West near Neenach School, and Avenue D from 245th Street West to Route 138's north junction with State Route 14. The Lancaster Freeway has four lanes, two for each direction of travel. Both Lancaster Road and Avenue D are 2-lane conventional roads; Avenue D is on a straight alignment over its between 245th Street West and State Route 14. After its co-routing with the Antelope Valley Freeway
(SR 14) for approximately through
Lancaster and
Palmdale, it passes through Palmdale's eastside as four-lane Palmdale Boulevard, 47th Street East, and Fort Tejon Road to Avenue T. At Avenue T it tapers to two lanes and continues straight ahead on Pearblossom Highway through
Littlerock,
Pearblossom, and
Llano to its west junction with
State Route 18.
Route 18's western terminus siphons off
Las Vegas-bound travelers from 138. At its west junction with
State Route 18, State Route 138 turns southeast on Antelope Highway to the
Los Angeles/
San Bernardino County line where it loses its alternative name, Antelope Highway. Between the county line and
Interstate 15, State Route 138 traverses very mountainous and scenic terrain and it connects with
State Route 2 that leads to winter resort areas in the
San Gabriel Mountains used largely by residents of the
Los Angeles metropolitan area. State Route 138 then descends through the West Cajon Valley and crosses
Interstate 15 in the
Cajon Pass. From
Interstate 15 to
State Route 173, near the northwest corner of
Silverwood Lake, traffic on State Route 138 is rather sparse. The remaining road past Silverwood Lake is mountainous, narrow, and twisting, and not a prime mountain route to the San Bernardino Mountain resorts. The entire segment from Interstate 15 to the eastern terminus of State Route 138 at Mount Anderson Junction is known as the El Cajon-Skyline Forest Highway. State Route 138 and 18 overlap each other in opposing termini, as SR 18's northwest most endpoint is in Llano with SR 138, while SR 138's southmost point is in Crestline with SR 18. Because of its twisting, mountainous segments and overloaded traffic conditions on its eastern leg, State Route 138 east of Palmdale and west of Interstate 15 is the site of numerous serious auto accidents as of 2004, according to
CHP data. One of the chief contributors to accidents on Route 138 of late is drivers passing on the two-lane highway in unsafe conditions. A notable accident in 2003 involved a pickup truck driven by an unlicensed driver leaving the roadway and plunging into the
California Aqueduct, killing four occupants of the vehicle and leaving the sole survivor quadriplegic. The State of California paid a $10 million settlement to the victims' family. The area surrounding the highway is also prone to brush fires and flash floods. SR 138 is part of the
California Freeway and Expressway System, and west of the western junction of SR 18 is 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. SR 138 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. The segment of SR 138 from I-15 in the Cajon Pass to SR 18 at Crestline is designated as part of the
Rim of the World Scenic Byway, a
National Forest Scenic Byway. '' ==Future==