In June 2009, the Governor of Texas vetoed a bill (SB 488) that would have required motorists to allow at least 3 ft when passing "vulnerable road users". A petition effort is trying to resurrect the measure.  I think it's probably a good thing to give motorists a "metric" to use when passing cyclists, but I don't think a law like this really offers a panacea of any sort.  You could even argue that it might further inflame the situation, if drivers feel its a one-sided law designed to place restrictions on them, while cyclists are allowed to ride disrespectfully or carelessly with little consequence.  The same law should address the responsibilities and rights of both parties.  Perception is everything.  If the public perceives Safe Passing gives further immunity/protection to a group they perceive as often arrogant and law-ignoring, the result could be self-defeating.  Feel free to sign the petition but don't let it stop there -- be Polite & Right.