While I applaud the effort, there is little chance that people will give up driving just because their employer will get a tax break for it.  Employers will have to have some pretty significant sticks and carrots in order to get their employees out of their cars.  A carbon tax on DRIVERS would be a much more effective approach, but would probably not be politically popular (though in SF, who knows?), which is the most likely reason that a politician like Newsom won't try that.