The expansion of car services hailed by apps like Uber and Lyft would be sharply limited citywide for as long as 14 months under legislation supported by Mayor Bill de Blasio and being introduced in the City Council.

Citing increased congestion in Manhattan, officials said the city needed to study the impact on traffic flow of the competitors for yellow and green cabs and "make informed policy."

The restrictions would be based on the number of vehicles a dispatching base currently has in its fleet, with the greatest restrictions placed on bases with the most vehicles.

For example, a base with 500 or more vehicles in service as of June 15 would be limited to growth of at most 1 percent, while one with 19 or fewer can grow 15 percent or less. There are no restrictions now on how fast a base can grow.

Taxi and Limousine Commission Commissioner Meera Joshi said the app-based services have their "downsides" -- which the study would explore.

"What happens to congestion in Manhattan when you start adding lots of vehicles to the fleet?" she said in a conference call Tuesday convened with reporters. The de Blasio administration distributed a slideshow highlighting a 9 percent decline in average Manhattan traffic speeds, to 8.51 miles per hour to 9.35 between 2010 and 2014, and a 5 percent decline in rush-hour MTA bus speeds between 2013 and 2014.

The legislation will be reviewed at a hearing Monday morning of the City Council transportation committee.

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Uber spokesman Matthew Wing accused the administration of borrowing from a proposal put forward by a coalition of yellow taxi medallion owners "to protect the status quo, and limit competition and innovation."

"Unfortunately, this would reverse improvements made by Uber and others to our transportation system and most notably, stand between New Yorkers looking for work and their opportunity to make a better living," Wing said.

The yellow-cab trade group has proposed a cap on the kind of cars dispatched by Uber and Lyft.

Yellow cabs -- the only ones legally allowed to be hailed the traditional way citywide -- have seen a decline in business with the rise of app-hail services. Green cabs can accept street hails in northern Manhattan and the other boroughs.