The Arroyo Seco Parkway, also known as the Pasadena Freeway, is one of the oldest freeways in the United States. It connects Los Angeles with Pasadena alongside the Arroyo Seco seasonal river. Mostly opened in 1940, it represents the transitional phase between early parkways and later freeways. It conformed to modern standards when it was built, but is now regarded as a narrow, outdated roadway. A 1953 extension brought the south end to the Four Level Interchange in downtown Los Angeles and a connection with the rest of the freeway system. The road remains largely as it was on opening day, though the plants in its median have given way to a steel guard rail, and most recently to concrete barriers, and it now carries the designation State Route 110, not historic U.S. Route 66. Between 1954 and 2010, it was designated the Pasadena Freeway. In 2010, as part of plans to revitalize its scenic value and improve safety, the California Department of Transportation (Caltrans) restored the roadway's original name. All of its original bridges remain, including four that predate the parkway itself, built across the Arroyo Seco before the 1930s. The road has a crash rate roughly twice the rate of other freeways, largely due to an outdated design lacking in acceleration and deceleration lanes. The Arroyo Seco Parkway is designated a State Scenic Highway, National Historic Civil Engineering Landmark, and National Scenic Byway. It was listed in the National Register of Historic Places in 2011.