Does carsharing really reduce overall driving?

The research shows carsharing really is green.

At the Share conference that I covered for this week’s Guardian, there were wildly divergent claims for how many vehicles carsharing companies such as City Car Share, Zipcar, and Getaround take off the road. I was also a little skeptical of claims that carsharing dramatically reduces overall driving and greenhouse gas emissions, so I decided to take a deeper look at the issue.

“For every car that is shared, we take seven cars off the road,” Board of Supervisors President David Chiu said during his presentation. The next day Getaround founder and spokesperson Jessica Scorpio cited a study claiming that 32 cars get taken off the road for every shared vehicle.

Luckily, one of the country’s top researchers in this area is right in our backyard. UC Berkeley civil and environmental engineering professor Susan Shaheen heads the school’s Transportation Sustainability Research Center and has been doing peer-reviewed studies on car-sharing for almost 20 years.

Her research, which is consistent with the body of academic research on carsharing from around the world, has found that each shared car takes between nine and 13 other cars off the road, figures that she says are amazingly consistent around the world. That big reduction is because households that have cars tend to get rid of at least one of them when they sign up for carsharing, while car-free households that want access to a car will choose (as Shaheen says is the case for about 25 percent of the people in each group, which adds up to 90,000-130,000 fewer cars on the road nationwide).

But Shaheen told us that she’s highly skeptical of the study showing 32 cars being taken off the road, an industry-sponsored study that was far less rigorous than her work, and whose authors intially wouldn’t share their work with her when she requested it. “It appears to be some kind of idealized number,” Shaheen told me. “I take this stuff pretty seriously.

The part about up to 13 cars being taken off the road has always made sense to me, and it’s certainly a benefit to cities have fewer overall cars on the road, particularly as they use parking spaces on public roads. But I was more skeptical of the claim that overall vehicle miles traveled (VMT) is reduced by carsharing.

Shaheen’s biggest study (“Impact of Carsharing on Vehicle Holdings,” a 2009 study she did with Elliot Martin and Jeffrey Lidicker) found overall VMT was reduced by 27 percent, even though her study frankly admits that about 60 percent of carsharing customers come from car-free households.

How can that be? Doesn’t it seem like driving would increase when you give more people access to something as expensive as an automobile, particularly in a small, congested city like San Francisco that has such a variety of other good transportation options? Shaheen does admit that one study focused specifically on San Francisco did indeed find that overall VMT does increase among carsharing customers in their first year using the service.

But the studies by Shaheen and other researchers show that VMT among carsharing customers drops in subsequent years, often quite dramatically, as people figure out that it’s not really so hard to get around by public transit, bike, or on foot. “When people use carsharing, they use it less and less and less,” Shaheen told us.

And when it comes to air pollution and greenhouse gas emissions, Shaheen said her studies and those of other researchers — including the 2010 “Greenhouse Gas Emission Impacts of Carsharing in North America,” who she and Martin did for the Mineta Transportation Institute at San Jose State University — found dramatic reductions.

“This study contributes to mounting evidence that carsharing is lowering GHG emissions

by providing people with automotive access on an as-needed basis,” the study concludes, with the reduction in VMT compounded by the fact that carsharing encourages people to get rid of older, more polluting cars and instead drive new, more efficient vehicles.

Still, despite all of that evidence, Shaheen admits that it’s tough to say carsharing causes less overall driving in the city of San Francisco, although she thinks it’s likely that it does. Not only is her survey based on self-reported data, but it’s also based on national aggregations that can’t be unpacked to comment on specific locales.

And her study predated rapid and drastic changes on the streets of San Francisco over the last five years, where bike lanes and ridership have been expanded, bikesharing has been introduced (another area that Shaheen has studied in detail), Muni has had its ups and downs, the population has increased, parking costs have increased and morphed, and Lyft and other ridesharing companies have filled the streets with a new category of cars (that latter development is the subject of her latest research project that is now underway).

“Things are changing really rapidly,” she told us.

Each of those variables affect whether someone chooses to drive a car, and they can be constantly shifting. For example, driving might become a far less attractive option as automobile congestion increases, particularly if the city expands the capacity for cyclists and Muni riders.

Shaheen is also looking forward to technological advances in data collection, allowing her to use less self-reported data, something she is already able to do with Bay Area BikeShare: “With bike sharing, they are so transparent. They share all the data, it’s like a party for me.”

So as carsharing and ridesharing companies seeks to bolster their claims to being an unqualified benefit for society, those companies should be willing to share detailed usage data with Shaheen and other independent researchers, which will help us all move beyond the hype to make informed public policy decisions.

“This is important,” Shaheen told us. “I take this very seriously because I want these to be numbers that policymakers can use.”  


Posted by Guest on May. 23, 2014 @ 5:13 pm

If you'd read before commenting, then you'd know that I'm not criticizing carsharing, and that the answer to the question in the headline appears to be: Yes. 

Posted by steven on May. 23, 2014 @ 5:23 pm

If I did that, there's no way I could troll as prolifically as I do. Once again, you prove how clueless you are, Steven. What, do you think this is the only site I troll? You have no idea how hard it is to troll a dozen left wing sites every day and post the first comment on each and every article.

Posted by Guest on May. 24, 2014 @ 7:48 am
Posted by Guest on May. 24, 2014 @ 8:44 am

A good question to ask would have been "What percentage of car sharing is used for intra-city trips".

Comparing car sharing to bicycles and public transport doesn't make a whole lot of sense if people are using it to visit Grandma in a retirement home outside of Sacramento.

Which is more likely to be the type of trip that would motivate someone to use Zip Car as opposed to going to a different neighborhood in San Francisco.

Posted by Guest on May. 23, 2014 @ 6:11 pm

Wait, what? Zipcar is designed around intra-city trips of a few hours or less. You pay for the entire time that you have the car, up to $79 a day. If you need to visit grandma in sacramento, renting a car from a traditional rental is likely to be a better deal.

Posted by Guest on Jun. 16, 2014 @ 8:41 am

Carsharing is meant to be used for short trips around town, and the pricing structure is set up to make you want to use cars efficiently, and return them for the next driver.

It's almost always cheaper to rent a car from a car rental company for longer trips,sometimes a lot cheaper.

That's the point.

Posted by Guest on Jun. 16, 2014 @ 9:56 am

Anyone know of a good spellcaster? I could use their services. Thanks in advance.

Posted by Guest on May. 23, 2014 @ 10:57 pm

If only I could get my lover back

Posted by Guest on May. 24, 2014 @ 1:43 am

I'm here bapa

Posted by Guest on May. 24, 2014 @ 6:52 am

I'm here

Posted by Guest on May. 24, 2014 @ 6:50 am

I will always be here!

Posted by Guest here on May. 24, 2014 @ 6:58 am

How will I find you at Carnavale, amigo?

Posted by Guest on May. 24, 2014 @ 7:34 am

Thanks to City Car Share, I dumped my car about 10 years ago.

A day without car ownership is like a day without jock itch.

Posted by Guest on May. 24, 2014 @ 10:35 am
Posted by Guest on May. 24, 2014 @ 10:46 am

While this story largely reflects the conversation that I had with Steven regarding carsharing impacts. I would like to provide some clarifications. During our interview, I stated that I could not discuss SF carsharing impacts specifically with respect to our research on N. American carsharing, as we agreed to aggregate our data on a N. American level with the study participants and carsharing operators. This does not mean that carsharing does not take cars off the road or reduce vehicle miles traveled (VMT) in SF. I directed Steven to research conducted by Professor Robert Cervero and colleagues at UC Berkeley on carsharing in SF and how VMT changed over time in their longitudinal study (the study was conducted across multiple years). This study showed VMT reductions over the course of the study (and after the first year).

Prior to our interview, I provided our research papers from our N. American carsharing study. This documentation explains in detail how VMT is reduced across the study population. This change is a net effect vs. a uniform effect across individuals in the study. Households reducing car ownership are largely responsible for the VMT reductions, which I noted during the interview. Research from across the globe on carsharing indicates that VMT reductions occur due to auto sales, postponed auto purchases, and modal shifts. Again, behavioral change is not uniform across study populations in carsharing or bikesharing research. It is the net effect of the mode that is key to focus on in understanding the overall VMT or emission impact.

Posted by Guest on May. 24, 2014 @ 7:14 pm

I'd guess that driving is reduced. When you own a car, you're compelled to use it, and you use it more casually and make more on-the-fly decisions ("Hmmm, maybe I'll buzz over to Emeryville and wander aimlessly through IKEA") vs. "I've signed this car out for 2 hours and am paying for time/mileage, so I'm going to Rainbow for 45 minutes, then the furniture store, then home to unload."

Also, let's assume that you don't own a car, so you just lose that mindset of driving everywhere, rather than making more rational decisions about walk/transit/bike/carshare.

Posted by Guest on Jun. 16, 2014 @ 10:04 am

Compared to the cited paper, the claims in this article seem patchy at best. Thanks for the clarification and for pointing to the Cervero work!

Posted by Chris McCahill on Jun. 20, 2014 @ 7:51 am

Even if you said that for every 1 car shared, 5 cars were taken off the road, I would have applauded. But 7, or 13? Awesome.

Posted by Rocket on May. 24, 2014 @ 8:42 pm

Want reliable data? Want to back up you claims with facts and not just feelings? "Commercial in confidence" - Course101 in avoiding transparency!

Posted by Guest on May. 25, 2014 @ 9:45 pm

We live in DC now -- and with the amazing bikeshare and many carshare options (including Car2Go), we took the leap and sold our car last year. And I don't have the figures, but we drive way way way less. Like WAY less. Most of the increase is bikeshare for weekend chores and activities, but we do both zipcar and car2go when we have a lot to carry. A big thing that makes it do-able is the amazing Metro system in DC. SF needs to continue to spend big to build out the MUNI underground system -- the Chinatown tunnel is a good start.

Posted by Guest on May. 26, 2014 @ 1:49 am

If you are interested in sustainability, please do not patronize any carshare service that utilizes gas-guzzling limos, town cars or large SUV's. Is it so hard to make the slightest "sacrifice" by using a service that generally involves smaller cars? No, I have no financial stake in any of these services, nor do I use them. But in this supposedly informed, liberal and enviro-conscious city, I am appalled at the lack of attention paid to this issue. Big, (usually) black carshare SUV's careening around City streets is what I saw in my last visit to NYC last fall and now they are here in a big way. Town cars with one passenger? Whahzzup with that? Make a statement by avoiding them. A small vehicle will get you around just fine. No one is going to see you behind that dark glass anyway.

Posted by Guest on May. 26, 2014 @ 1:02 pm

vehicle. And taking two smaller vehicles uses more fual than one large vehicle.

Sharing services like Uber and ZipCar reduce the number of cars on the road.

Posted by Guest on May. 26, 2014 @ 1:24 pm

If people chose to give up cars, great. If people are willing to ride their bikes more often, great or even take the bus more. The fact is we still live in a car centered world, so the idea of car sharing is great.

Won't work in suburb or the country.

Posted by Garrett on May. 27, 2014 @ 5:27 pm

Yes, that's true. Car sharing only works in densely populated areas.

But I long for the day when nobody in the more densely populated parts of San Francisco (meaning just about everywhere except the Sunset and Richmond) realizes that cars are unnecessary.

For me, on Russian Hill, a car was a burden. I use City Car Share or Zipcar for short trips and rent a car from one of the agencies for longer trips.

Saves lots of money and insurance/maintenance hassles.

Posted by Guest on May. 28, 2014 @ 9:07 am
Posted by Guest on May. 28, 2014 @ 10:02 am

Does market pricing for parking to maximize turnover really reduce overall driving?

Posted by marcos on May. 28, 2014 @ 10:23 am

the purpose is to make going somewhere by car more feasible by increasing the probability that there will be street parking at your destination.

Posted by Guest on May. 28, 2014 @ 10:40 am

Yes. It reduces the amount of time spent driving in circles looking for parking and discourages frivolous trips by increasing the price of parking (which is still pretty cheap overall). Those that decided to drive benefit by having parking more readily available.

Posted by Guest on Jun. 16, 2014 @ 8:37 am

¤ I just saw a City Car Share ad that suggested that I needed a car to be both "wicked sexy" and "crunchy green." It was targeted, of course, to users of public transit. Not quite as bad as the ZipCar ads (which depict able-bodied people half my age who "just need a car" to do things I do without one, or to go out drinking at night), but even so, the association of cars with sex is idiotic.

I'm glad they're having the impact described here, but I have to wonder why they're so interested in expanding market share by poaching from public transit.

Posted by Jym Dyer on Jul. 01, 2014 @ 7:08 am

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