Keith Srakocic/AP

These programs promise big things for cities, but changes in habits—like parking—take time.

Bike-share programs start off with big, bold New Year’s Resolution-style ambitions. They promise to save cities money, make people healthy, and convert commuters to the Gospel of Good Cycling.

But just like setting attainable goals for the new year, we should look to small changes in habit—rather than an overnight transformation—to measure a bike-share program’s success.

The behavior changes produced by bike share are subtle, but could be significant. That’s the main takeaway from a recent working paper on Social Science Research Network (SSRN) by Konstantinos Pelechrinis at University of Pittsburgh and Beibei Li and Sean Qian at Carnegie Mellon University.

The paper looks at whether a bike-share program decreases demand for parking spaces for cars. The study looked specifically at Pittsburgh’s Healthy Ride, the city’s bike-share program that launched in 2015.

Researchers compiled transactions from the Pittsburgh Parking Authority meters and ridership stats from Healthy Ride stations to compare patterns in two neighborhoods—Shadyside and Squirrel Hill in Pittsburgh’s East End.

The program created the right conditions for a natural experiment. The neighborhoods are fairly similar in terms of demographics and density. The major difference is in the availability or lack of bike-share stations.

Healthy Ride installed seven stations in Shadyside—the cluster of stations north of Fifth Avenue below in the Healthy Ride map—and no stations in Squirrel Hill—just south of Fifth Avenue. The locations are mapped below:

(Healthy Ride Pittsburgh)

To estimate the effect that bike share had on car trips, the researchers paired Shadyside’s bike dock data with parking meter data from both neighborhoods.

The researchers measured the differences in parking rates in the month before and a month after the bike-share stations were installed in Shadyside (May 2015 and July 2015). The researchers then charted the hourly difference between parking events in Shadyside and Squirrel Hill. The difference is illustrated below:

The difference-in-differences coefficient for parking in Shadyside compared to Squirrel Hill after adding bike share stations. (Konstantinos Pelechrinis et al./SSN)

After bike share was introduced, the researchers found a statistically significant difference in demand for parking between the two neighborhoods during morning and afternoon commuting hours, as well as a significant effect during lunchtime hours. The study also compared those numbers to 2014 parking levels to ensure larger trends in either neighborhood were not skewing the results.

A subtle shift adds up

Bike-share trips replaced at most about 69 car trips per day, out of 2,250 daily parking events in the neighborhood of Shadyside. This is a 2 percent decrease in parking demand (adjusted for the lost curb parking space for the installation of the bike docks) after the program’s launch in 2015.

Okay, so that’s not exactly a sea change in commuting patterns. But while those numbers are small, the benefits of that change could add up.

The average distance traveled towards the Shadyside stations was about .85 miles. Over the course of those nearly 69 trips, that’s about 58.6 fewer miles driven each day.

The researchers estimate that level of trip replacement over a month would produce approximately 1,346 fewer car trips, 82.5 fewer gas gallons, 76,470 calories burnt, and 0.73 fewer metric tons of CO2 emissions from trips to Shadyside.

The researcher Konstantinos Pelechrinis tells CityLab his team is using a much larger data set to look for evidence of a similar phenomenon throughout the whole city of Pittsburgh, where even a small decline in driving could have a much more significant effect.

Obviously, the subtle shift to bike share is no substitute for tackling global climate change, a charge that cities will likely need to lead. But at least good signs of changing habits make that challenge seem less Sisyphean—even if biking Pittsburgh’s hills can be hellacious.

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