would presumably have carried Pacific Electric Railway red cars), but this plan was never fully implemented. Planning and construction During World War II, transportation bottlenecks on Southern California roads and railways convinced many that if Southern California was to accommodate a large population, it needed a completely new transportation system. The city of Los Angeles favored an upgraded rail transit system focused on its central city. However, the success of the Arroyo Seco Parkway, built between Los Angeles and Pasadena in 1940, convinced many that a freeway system could solve the region's transportation problems. Leaders of surrounding cities, such as Whittier, South Gate, Long Beach, and Pasadena, accordingly called for a web of freeways to connect the whole region, rather than funneling their residents out of their own downtowns and into that of Los Angeles. Pro-freeway sentiments prevailed, and by 1947, a new comprehensive freeway plan for Los Angeles (based largely on the original locally planned 1930s system, but without the light rail tracks in the median strips of the freeways) had been drawn up by the California Department of Public Works (now Caltrans). San Diego soon followed suit, and by the early 1950s, construction had begun on much of the region's freeway system. Proposed/future freeways Caltrans or local transportation agencies have identified the following priority freeway projects: A toll road that will go through a tunnel in the Santa Ana Mountains from Irvine to Corona. Upgrading State Route 210 to Interstate standards and renumbering the route Interstate 210. A new freeway, the Mid County Parkway, from Interstate 215 in Perris to State Route 79 in San Jacinto. An extension for Interstate 710, the Long Beach Freeway, to its originally planned terminus at Interstate 210, Foothill Freeway, in Pasadena, via a tunnel underneath the city of South Pasadena or some other means. Caltrans, however, cancelled the project in November 2018. An extension to the State Route 241 toll road to meet Interstate 5 in or near San Clemente. Upgrading State Route 71, the Chino Valley Freeway, to a full controlled-access freeway north of State Route 60, the Pomona Freeway, to Interstate 10, the San Bernardino Freeway, in Pomona. Upgrading State Route 55, the Costa Mesa Freeway, from south of its current freeway terminus at 19th Street in Costa Mesa to State Route 1, Pacific Coast Highway, in Newport Beach, potentially via a tunnel. Construction of the High Desert Corridor, a