The Uber wave that prompted Mayor Bill de Blasio to try to cap the ride-share company's growth appears to be gaining strength: The number of Uber drivers in New York City has almost doubled in the past year, and fare revenue per driver also has increased, according to the company.

Last September, 10,000 UberX drivers, which operate as black cars, were roaming the streets of New York City. By March 2015, about 13,000 car-service drivers were using Uber's app to arrange rides with passengers. By September, that number had grown to 20,000, as well as another 4,000 yellow- and green-cab drivers who can be hailed through Uber. Taken together with the company's limo, SUV and carpool services, there are now over 30,000 Uber-affiliated vehicles in New York City today.

According to a blog post that went up on Uber's website Tuesday, average UberX (non-taxi) gross fares per hour increased by 6.3% from September 2014 to September 2015. Last month, UberX drivers earned $39.30 per hour in fares on average, up from $36.96 last year. That figure is inflated by part-time Uber drivers who make themselves available when the company's surge pricing is in effect.

The San Francisco-based company says about 42% of its drivers are part-timers, logging into the service 15 hours a week or less. Also Uber drivers who frequently cancel rides, or whose customer ratings drop below 4.5 stars, can find themselves locked out of the system.

Uber says its drivers are spending less time cruising or waiting for customers to summon a ride, and more time with passengers in their vehicles. In September 2012, the first year Uber was active in New York, drivers spent 16 minutes per hour with passengers. That number has risen to 32 minutes in 2015.

Uber says it has grown the pie, meaning it has attracted riders who did not previously use car service as much, but its gains in market share have certainly put pressure on yellow cabs, livery cabs and black-car businesses. Credit unions that finance taxi-medallion purchases tried to force the city to stop Uber drivers from responding to smartphone hails, but a judge dismissed the lenders' lawsuit.

Which is not to say the city hasn't tried to stymie Uber in other ways. In June, Mr. de Blasio unveiled a plan to cap Uber's growth at 1% while his administration studied its impact on traffic congestion. Uber unleashed an ad campaign and an army of lobbyists, forcing the mayor to retreat. The administration is now conducting a four-month traffic study, with data that Uber agreed to provide, after which it will likely propose a new plan to limit the company's growth, restarting the fight.

The concept of Uber's rapid growth conforms to numbers the city used to justify its plan. More than 25,000 new for-hire vehicle licenses have been issued since 2011, increasing by 63% a market that includes livery cabs and black cars, according to data released by the Taxi and Limousine Commission during the summer. Much of that growth has occurred in the past year: At least 2,000 licenses were handed out in each month of fiscal 2015, which ended June 30.