In the 1960s, San Diego proposed to expand what is now known as State Route 163, the Cabrillo Freeway, through Balboa Park to an 8- to 10-lane freeway. Public protest stopped the freeway from expanding more than its existing four lanes, but not before a portion of the SR 163/I-5 freeway connection began construction. The built portion would have extended north over a pedestrian walkway. The stub is still visible today from the Bridle Trail in Balboa Park and connects to the SR 163/I-5 interchange, modeled after the "Four Level" US 101/SR 110 interchange in Los Angeles.