 Route 37 has been proposed to be built to freeway standards since the early 1950s. However, the proposal was met with many economic and environmental obstacles, making the task all but impossible for much of the route. Problems included a levee break in Vallejo which turned part of the land around the highway into a marsh that is home to endangered salt marsh harvest mice, and a section of highway known as "Blood Alley" for its high rate of fatal accidents.
