How to enforce 3-foot passing law to protect bicyclists

To those who say that laws requiring motorists to give bicycles a 3-foot gap when passing are unenforceable, consider what police in Austin, Texas, are doing.
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<a href="http://www.bikingbis.com/2013/09/16/how-to-enforce-3-foot-passing-law-to-protect-bicyclists/">http://www.bikingbis.com/2013/09/16/how-to-enforce-3-foot-passing-law-to-protect-bicyclists/</a>;