A Bay Area freeway once served as a guinea pig for a 1960s study on the feasibility of adopting a minimum speed requirement to help with the flow of traffic, but the results found California drivers to be much more fickle and unreliable than anticipated.

The report came as the state’s freeway network underwent massive changes in the mid-1960s when car culture became a hardened attribute of the American lifestyle. 

Slow drivers on state highways caught the ire of California Assemblyman Lee M. Backstrand from Riverside, who proposed a law that would establish minimum speed limits on the state’s highways.

The 1965 California Legislature asked the Department of Public Works to study the impact of establishing minimum speed limits on a lane-to-lane basis on multiple-lane highways. Lanes were divided into three speeds: 50 mph, 55 mph and, in the left two lanes, 60 mph.

The State Division of Highways — the predecessor to Caltrans — selected four highway sections across the state to study for four weeks in June 1966.

Among them was the Bayshore Freeway, connecting San Francisco with San Jose along the west shore of San Francisco Bay.

Originally called the Bayshore Highway, the road was particularly perilous in the 1940s and 1950s because it was divided by just a double yellow line. The roadway earned the nickname “Bloody Bayshore” from the Palo Alto Daily News due to its crash rate, which was twice the average of California highways. The highway was eventually revamped into a freeway and became part of U.S. Route 101 following the 1964 state highway renumbering overhaul. 

The minimum speed study also looked at two highway sections in the Central Valley — Interstate 80 near Roseville and I-80 near Dixon — and a section of what is now Interstate 110 called the Harbor Freeway in Los Angeles. 

These sites were selected because of their nearly straight alignment, with no sustained grades that would significantly affect speeds, leading researchers to believe the conditions created an atmosphere for high speeds.

Engineers with the State Division of Highways analyzed the Bayshore Highway between Peninsular Avenue and Ralston Avenue. 

They calculated the speed and volume of vehicles using a recording device called the Bureau of Public Roads Traffic Analyzer, which printed numbers on a paper tape displaying the speed of each car passing by. 

Based on data from observing more than 85,000 vehicles in a month, the study determined that minimum speeds were a bust and did not keep slower drivers to the right; instead, the minimum speeds had the unintended consequence of clogging the left lanes.  

“Minimum speeds by lane cannot be considered as a relief for traffic congestion,” the report’s conclusion begins. “… Probably the most unexpected result of this study was the fact that the minimum speed signing generally moved more drivers into the left lanes instead of moving slow drivers to the right lane. This was contrary to the intent of the signs, i.e., that drivers should keep right and pass left.”

The California Highway Patrol and the Los Angeles Police Department, who enforced the study, reported that 13% of drivers cited for violating the minimum speed confused the word “minimum” for “maximum.”

The report concludes by noting, “Minimum speed by lane signs would only add clutter to the highways, with definite operational and safety disadvantages.”

Caltrans’ 2020 manual for setting California speed limits states, “No person shall drive upon a highway at such a slow speed as to impede or block the normal and reasonable movement of traffic unless the reduced speed is necessary for safe vehicle operation, because of a grade, or in compliance with law.”

It also notes that the use of minimum speed limits is not commonly practiced in California.