Crunching some numbers on Paris bike-sharing program

Bike-sharing offers modest emissions reductions, and no reason to complain.

On the first anniversary of Vélib, the Times dishes up some stats on Paris’ popular bike-sharing program:

• Riders took 27.5 million trips in the first year.
• The current pace is about 120,000 trips per day.
• The program includes 20,600 bikes.
• The 1,450 self-service rental stations are available every 300 yards.
• The bikes are heavy and expensive — $3,460 and 50 lbs — built to withstand theft, mistreatment, and heavy riding.
• Nevertheless, 3,000 bikes have gone missing, about 15% of the total.

Such programs, done right, do a fantastic job of boosting bicycle ridership. One thing they don’t necessarily do, however, is reduce a lot of carbon emissions. I built a simple model using the cited figures, and added in assumptions about average trip length, the number of displaced car miles, average fuel efficiency, etc. The results are necessarily rough, but I estimate the program is currently reducing maybe 40,000 metric tons of CO2 per year, about the amount saved by removing 5,700 cars from the road. (This suggests that it takes about 3.6 shared bicycles to replace a car.)

40,000 tons ain’t bad, and with more generous assumptions and future growth factored in the number might double or even triple. But even that would be a modest figure in the context of the price tag — $142 million to set up the program, and millions in maintenance costs per year. The cost per ton of CO2 pencils out in the many hundreds of dollars, a price that makes solar photovoltaics look like an incredible bargain.

Which is not to say that bike-sharing programs are a bad idea. On the contrary, the costs of the Vélib program are being entirely borne by a private company in exchange for advertising rights, a deal that is proving handsomely profitable for everyone involved - company, city, and citizens. But it does suggest that bike-sharing shouldn’t be oversold as a solution to climate change, but instead should be seen as part of the movement toward green, livable cities that prioritize citizens over cars.

In the meantime, New York gazes across the pond at Paris and likes what it sees. The city just put out a “Request For Expressions of Interest” to determine what a similar program over here might look like. Compact, flat, and bustling, New York is ripe for bicycles.

Update: Spreadsheet with calculations now posted (xls). Note that my assumptions are really generous. It’s unlikely that the average trip is three miles (96% of trips take less than half an hour); it’s unlikely that 80% of trips displace driving (many displace walking or public transportation); and the average fuel economy in Paris is likely higher than 20 mpg. So probably the system is saving even less than 40,000 tons of CO2 per year.

Image by Ed Alcock for The New York Times.