Legal Question in Administrative Law in California

Re: legal to drive

It is illegal to operate a car when you can not do safely. If a policeman stops you, he feels you are unsafe and the court will likely accept his word.

Re: legal to drive

It is illegal to drive with your physical or mental ability impaired. With some tings such as alcohol, the degree of impairment making it illegal to drive is at least semi-defined: you are legally impaired at over .08 blood alcohol percentage. You can also be impaired in fact at lower alcohol levels. Things like leg casts are too variable to be described in statutes, so it is left to the wisdom of the judge or jury to decide (after the fact) if your ability to handle the accelerator and brake were significantly impaired by the cast. The same reasoning would apply to driving while sleepy, with eyes dilated following an eye exam, while ill, and so on.

Remember that in addition to the possibility of arrest, you might be involved in an accident where you would be sued in a civil action for negligence.