Nash and Joe drive across the upper deck of the Oakland-San Francisco Bay Bridge in order to visit Linus Mills at his lecture on the UC Berkeley campus, which is east of SF. However, the upper deck of the Bay Bridge is for westbound traffic, so the officers would have to drive against the flow of traffic. This same mistake was also made in The Graduate (1967) - presumably because the lower deck (for eastbound traffic) isn't as picturesque.