The entirety of I-605 is defined in section 619 of the
California Streets and Highways Code as
Route 605, and that the highway is from: (a)
Route 1 near
Seal Beach to
Route 405.(b) Route 405 to
Route 210 near
Duarte. The segment defined in subdivision (a) remains unconstructed, and is not included in the
Federal Highway Administration (FHWA)'s Interstate Highway route logs. The southern terminus of I-605 is at the
San Diego (
I-405) and Garden Grove (
SR 22) Freeways in
Seal Beach. This interchange was built to accommodate the aforementioned southern extension to
SR 1. From there, I-605 runs roughly north through the
Gateway Cities of the
Los Angeles Basin. It then shifts north-northeast, crossing the
Whittier Narrows and across the
San Gabriel Valley. I-605 then ends at its junction with the
Foothill Freeway, (
I-210) just south of the
Irwindale–
Duarte border. Ramps from I-605 then extend north to
Huntington Drive in Duarte. I-605 follows most of the length of the
San Gabriel River from the San Diego Freeway in Seal Beach to the
Santa Fe Dam. Typically dry riverbed and flood basins are visible from many portions of the route, especially near the northern terminus. In the mid-2000s, a
HOV lane was added for motorists with two or more people to use between I-405 and I-10. The HOV lane ends at I-10 and there are no plans to extend it to I-210 at this time. With the addition of the HOV lane, the left shoulder was eliminated to avoid massive costs to widen the freeway. The highway also suffers from traffic jams regularly, especially the junction with
I-5 (the
Santa Ana Freeway). Newer signs with exit numbers replaced the older signs between the Orange County line and I-10 in 2016, with the completion of the I-605 and I-10 junction improvement. I-605 is one of the only Southern California freeways without destinations (
control cities) such as "
Seal Beach" or "
Irwindale" since its opening. Rather, cardinal directions ("NORTH" or "SOUTH"), and a simple "THRU TRAFFIC" designation in place of control cities, are used on signs along I-605 itself. I-605 is part of the
California Freeway and Expressway System, and 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. I-605 is designated as the San Gabriel River Freeway, as named by Senate Bill 99, Chapter 1101 in 1967, and amended to section 619 of the California Streets and Highways Code. ==History==