Although many South Pasadena residents opposed the division of the city that the parkway would bring, the city's voters elected supporters in the 1936 elections. The state, which had the power to put the road where it wished even had South Pasadena continued to oppose it, approved the route on April 4, 1936. The route used the Arroyo Seco's west bank to near Hough Street, where it crossed to the east and cut through South Pasadena to the south end of Broadway (now Arroyo Parkway) in Pasadena. Another project, the Arroyo Seco Flood Control Channel, was built by the Works Progress Administration before and during construction of the parkway to avoid damages from future floods. A number of state engineers toured East Coast roads in early 1938, including Chicago's Lake Shore Drive, full and modified cloverleaf interchanges in Massachusetts and New Jersey, and Robert Moses's parkway system in New York City. The parkway was the first road built in California under a 1939 freeway law that allowed access to be completely limited to a number of specified points. Although, in some areas, it was possible to use a standard diamond interchange, other locations required folded diamonds, or, as the engineers called them, "compressed cloverleafs", where local streets often took the place of dedicated ramps, ending at the parkway with a sharp right turn required to enter or exit. The highway was designed with two lanes and one shoulder in each direction, with the wider inside (passing) lanes paved in black asphalt concrete and the outside lanes paved in white Portland cement concrete. The differently-colored lanes would encourage drivers to stay in their lanes. (By mid-1939, the state had decided to replace the shoulders with additional travel lanes for increased capacity; except on a short piece in South Pasadena, these were also paved with Portland cement. So that disabled vehicles could be safely removed from the roadway, about 50 "safety bays" were constructed in 1949 and 1950.) The engineers used a design speed of , superelevating curves where necessary to accomplish this. (The road is now posted at .) Despite the freeway design, many parkway characteristics were incorporated, such as plantings of mostly native flora alongside the road.