The city's green borough cab program appears poised to shift into high gear -- and that's a pleasant surprise.

Under Mayor Michael Bloomberg, the city Taxi and Limousine Commission put almost 5,000 of the metered borough taxis on the streets -- for legal hails in the outer boroughs and in upper Manhattan.

The green cabs caught on fast in areas where yellow taxis seldom cruise. But no one knew which way the new program would go when Mayor Bill de Blasio took office.

De Blasio had accepted tens of thousands of dollars in campaign contributions from the yellow cab industry, which views the green cabs as competitors.

And when asked as a candidate about the program, his answers often grew vague: "There's a particular balance to be struck" as the program goes forward, he noted in one debate. He said it was an issue with "many moving parts."

But this afternoon Meera Joshi, the mayor's nominee to head the commission, is expected to win City Council approval -- and that's a great sign.

She has acknowledged the popularity of the borough cabs. And she has cited their value serving neighborhoods that are neglected by mass transit and yellow cabs.

The borough program will get some scrutiny later this year when City Councilman Ydanis Rodriguez of upper Manhattan, chairman of the Transportation Committee, holds hearings to see what fine-tuning might be needed as the rollout expands to 18,000 cabs. There's lots to discuss.

The city's taxi industry is all about turf. Are green cabs cruising where they're supposed to? Are the yellow cabs playing by the rules? How are the livery drivers in the black sedans faring in the new pecking order? And most crucially: How well are green cabs distributed in formerly underserved areas? There's evidence that clustering in the most popular spots of each borough is a problem.

But the take-away is that program is working.

No politician at the moment seems eager to anger the millions of people who suddenly can make street hails. The program has come too far too fast for de Blasio or any other politician to slam on the brakes.