The Bloomberg administration has worked tirelessly to turn bicycling into a mainstream mode of getting around New York, creating more than 200 miles of bicycle-only lanes and placing protected bike paths on major thoroughfares like Broadway and Ninth Avenue.

"New York City is the bicycling capital of the United States," boasts the city's transportation commissioner, Janette Sadik-Khan.

But some critics are now arguing that bicycling is not nearly as popular in New York as the Transportation Department has claimed -- and the dissent is coming from some of the region's pre-eminent bicycling enthusiasts.

Current and former cycling advocates, although supportive of the city's efforts, have questioned the accuracy of data that is often used to justify the expansion of bike lanes (and the elimination of traffic lanes).

"There has definitely been a significant increase in cycling in New York," said John Pucher, a professor of planning at Rutgers University and the author of a wide-ranging report on cycling (pdf) released Monday. "But it's not clear how big the increase has been, because there has not been a good measure of it."

The numbers released by the Transportation Department, Dr. Pucher added, "are totally unrepresentative of New York City as a whole."

The Transportation Department said the number of New Yorkers who bike to work grew by 26 percent in 2009, and that bicycle commuting has doubled in seven years. Using that data, Transportation Alternatives, an outspoken advocacy group, estimated that 236,000 New Yorkers ride bikes every day.

But those numbers are based on counts taken at popular biking spots like the East River bridges, the Hudson River bike path, and the Manhattan terminal of the Staten Island Ferry. Critics argue that these figures cannot be extrapolated to reflect bicycling trends elsewhere in the city, where gains have been slower.

Dr. Pucher said the city's methodology may be inflating the actual growth of ridership in the city by as much as 100 percent. "It's not a minor overstatement," he said.

Dr. Pucher's doubts about the numbers are shared by Charles Komanoff himself, the longtime architect of the Transportation Alternatives survey and the group's former president.

"The screenline number is as good a number as I think we have, even if it probably overstates the increase in overall cycling," Mr. Komanoff said, referring to the system used by the city to calculate bicycle ridership. But he added: "I do think that if I were to make the appropriate adjustments, we would still end up with 200,000 or more."

Officials at the Transportation Department defended its method of counting riders, noting that the data collected is presented as a snapshot of cycling at a particular location at a particular time. The department is also looking to expand the scope of its survey.

"As we bring new world-class bike facilities to our streets citywide, our expanded counts at key commuter corridors and at key project locations citywide are helping us see how cyclists are actually using the growing network," Ms. Sadik-Khan said.

Ms. Sadik-Khan also noted in an interview earlier this month that a bicycling network must be built in advance of demand, in order to encourage cycling. The department has pointed to a decrease in cyclist fatalities and an overall decrease in accidents as positive results of the city's expanded biking network.

Dr. Pucher, whose study was financed by the United States Department of Transportation, said he found discrepancies between the city's estimates and those of the Census Bureau's annual American Community Survey, which asks residents about how they get to work.

"There is no need to exaggerate the growth in cycling in this way, since there has been a lot of growth in cycling in the city since 2000," he said.

Mr. Komanoff admitted that some of the factors by which he calculates the citywide bicycling figure -- developed in the early 1990s -- need to be revisited.

But Wiley Norvell, a spokesman for Transportation Alternatives, acknowledged that his group might seek out a better methodology. "We're all on the same page that there's a dearth of hard data on cycling, even as biking surges dramatically," Mr. Norvell said.

Still, both critics and advocates agree that the city has seen an inarguable upward trend in cycling. And Dr. Pucher said he hoped his criticism of the Transportation Department would generate a more accurate understanding of cycling's popularity in the city. His true leanings may be construed from the outgoing message on his campus office voicemail, in which he identifies himself as "Car Free John."