That's ~5% of the state budget, and primarily financed by the gas tax, not the income tax. (Large projects funded with bonds)
Source: https://dot.ca.gov/-/media/dot-media/programs/research-innov...
Source: https://dot.ca.gov/-/media/dot-media/programs/research-innov...
Even though legislators might label or apportion some source of tax to some specific expense, in reality, they can always move it elsewhere (since they are the legislators). Therefore, it is always a question of which expense has political priority.