The California Streets and Highways Code defines Route 605 as " Route 1 near Seal Beach to Route 405. Route 405 to Route 210 near Duarte." However, the portion in subsection A has yet to be constructed. The southern terminus of I-605 is at the San Diego and Garden Grove Freeways in Seal Beach. From there, it 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, in Duarte, a small city located at the foothills of the San Gabriel Mountains. 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 Interstate 10. There are no plans to extend it to Interstate 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. Newer signs with exit numbers replaced the older signs between the Orange County line and Interstate 10 in 2016, with the completion of the I-605 and I-10 junction improvement. Guide signs along I-605 never included destinations such as "Seal Beach" or "Irwindale" since its opening. Rather, cardinal directions, 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 from I-405 to I-10 is known as the San Gabriel River Freeway, as named by Senate Bill 99, Chapter 1101 in 1967.
History
In 1957, the number for this route was proposed as I-13, as it is positioned approximately midway between I-5 and I-15. That number was rejected, as was the second proposed number, I-102. Finally, the designation I-605 was accepted in 1958. Interstate 605 began construction in 1963 and the first section was opened in 1964 from I-405 to SR 60. The newest section was opened in 1971 was originally signed as SR 243. There are plans to extend it to SR 1 further south in Orange County as SR 605, but strong community opposition means that it is unlikely that the alignment will ever be built.
