Since Mayor Michael Bloomberg announced his plan to create a new class of taxis allowed to make street hails outside the Manhattan core, most of the coverage has focused on the potential effect on yellow cab medallion owners’ profits or livery drivers’ earnings. Less has been written about the broader effect such a plan would have on the city’s transportation system as a whole (Cap’n Transit being a notable exception).

Taxis, after all, make up a significant component of that system. A 2006 report by Bruce Schaller, a former policy director at the Taxi and Limousine Commission and now a top DOT official, estimated that in 2004, yellow cabs drove 815 million miles each year, while livery cabs drove more than double that, 1.733 billion miles.

Now that the legislature has passed the plan — it still needs Governor Andrew Cuomo’s signature — we checked in with TLC Commissioner David Yassky to see how he views its wider impact. He argued that the outer-borough taxi plan would help reduce car ownership and improve traffic safety.

Though he couldn’t quantify the likely impact of the Bloomberg taxi plan on car ownership or trip mode-share, Yassky said that “I think we can say that we know what direction the numbers go in.”

“A healthy taxi market gives people an alternative to private car ownership,” he said. People currently use illegal street hails “to go home from the supermarket with heavy bags, to go to and from the subway stop if you live a mile from the subway, to go to church or visit friends on a Saturday or Sunday. Those are all things that you need a car to do outside Manhattan if there’s no decent taxi service… That’s the systemic impact.”

Yassky also made the case that the taxi plan would make livery drivers more likely to follow traffic laws and drive safely: “We see with the yellow taxis that when you have a valuable license, that gives the driver a stake in following the rules.” Certainly some yellow taxi drivers break rules, he said, but “they do have to worry that if they rack up too many driving infractions, they’re going to lose their livelihood.” That isn’t true in the underground market for livery cab street hails. “Since the drivers activity is illicit to begin with, we have no way to give them an incentive to follow the more mundane but important traffic rules,” he said.

Interestingly, Schaller’s 2006 report found that livery cabs generally had fewer crashes per mile than yellow cabs (both were far safer than private vehicles). The two classes of vehicle take different trips in different locations, so it’s possible either that Yassky’s intuitions are correct and liveries will become even safer, or that making liveries more like yellow cabs will push up their crash rate.

Yassky wouldn’t say whether legalization would make hailing a cab outside the Manhattan core more or less affordable. “Rates will be set through TLC rulemaking,” he said. “We’ll have to look at the economics of the industry.”