How have courts interpreted excuse instructions in a motor vehicle case?

Fuentes v. Panella, 120 Cal.App.2d 175, at page 183, 260 P.2d 853 at page 858, holds: 'But these cases do not stand for the proposition that excuse instructions can be given only where there is an admitted violation and the violator offers evidence of justification for such violation. The jury may believe that a violation of the law has taken place, and thus disbelieve the testimony to the contrary, but at the same time believe [137 Cal.App.2d 259] that such violation, under all the circumstances, was justifiable because of the circumstances.' However, that rule is of no comfort to defendants here because the circumstances of our case bring it within the other rule set forth, 120 Cal.App.2d at page 183, 260 P.2d at page 858: 'Of course, where there is no evidence at all of justification, or the surrounding circumstances do not show it, it is error to instruct on excuse.'