Bikesharing and CO2: Complicated, But Important to Get Right

There have been a couple of stories recently (in Climate Central and Grist) that try to get a handle on the carbon dioxide emission reduction benefits of the popular new bikesharing systems popping up around the country.

The short answer is: nobody knows for certain. And that’s a problem. If bikesharing were conclusively shown to reduce carbon dioxide emissions (or save oil, or avert car trips), the case for public investment in those systems would be strengthened.

The thinly-veiled skepticism of those pieces (especially the one in Grist), however, is a warning that when it comes to measuring the impacts of bikesharing and other new transportation options, there are lots of opportunities to get it wrong. As shared-use transportation grows in importance, advocates will need to keep an eye out for analyses that understate the importance of those systems by looking at only a small part of the picture.

Here’s where things tend to go off the rails: most surveys of the impact of bikesharing (and transit, for that matter) look only at short-term impacts on an individual’s transportation choices– for example, if you didn’t use bikeshare today, would you have driven a car, walked, taken transit or not traveled at all? (Or, alternatively, are you driving less now because of bikesharing? And, if so, how much less?)

To date, however, bikesharing systems have tended to exist in portions of cities where people already have multiple transportation options. The presence of bikesharing in cities like New York, Boston or D.C. will coax a few people out of their cars, but it will also coax some people out of transit or off the sidewalk. If we only look at the short-term impacts of bikesharing, therefore, the results in most places are likely to look pretty “meh.”

Again, that’s a problem, because it enables bikesharing to be characterized as an inconsequential frill – something that’s nice for cities to have but not a real solution to global warming or anything else.

In reality, however, the short-term impacts of bikesharing are only the tip of the iceberg. Economics tells us (PDF) that it takes a while for changing circumstances – such as changes in the price of driving or the arrival of a new bikesharing system – to affect our transportation behaviors. That’s because the most important decisions we make that affect how we get around – where we live and whether we will own a car – are made infrequently. People tend to reevaluate their car ownership every few years, often when the time comes to replace an existing vehicle, and to reevaluate their housing at times of major life changes (the arrival of a child, perhaps, or a change in job).

If the presence of bikesharing in a community can be shown to influence those decisions of where to live and whether to own a car, the implications for carbon dioxide emissions would be profound. Many researchers (such as the esteemed Susan Shaheen at UC, Berkeley, PDF) and bikesharing operators (such as Capital Bikeshare, PDF) are already trying to get a handle on this by asking whether bikesharing has been influential in users’ decisions to sell or forgo the purchase of a car. So far, that research suggests that bikesharing can trigger small but significant reductions in car ownership. Since vehicle ownership is strongly correlated with the number of miles driven, it is quite possible that bikesharing’s most important climate impact will come not from the direct substitution of specific trips that would otherwise have been taken by car, but rather from its role in convincing people to forgo car ownership entirely.

Now, let’s go one step further: what if it were the case that the existence of bikesharing alone wasn’t enough to cause people to change their choice of housing or shed a car, but that the presence of bikesharing plus good transit plus good walkability plus the presence of alternatives like Lyft and Uber would be enough to spur those choices?

We’ve noted before on this blog that our tools for quantifying the cumulative climate benefits of transportation and land-use changes tend to miss the boat when evaluating synergistic policies that lead to systemic changes. The predominant “wedges-based” way of estimating the impact of emission-reduction policies assumes that, by and large, if you have one policy that reduces 2 units of emissions and another that reduces 3 units of emissions, the cumulative impact of the two policies will be to reduce emissions by 5 units. (This is an over-simplification, but not much of one.)

But what if several policies produce results that are greater than the sum of the parts – in other words, what if 2 plus 3 no longer equals 5, but rather equals 10? We hypothesized in our report, A New Way to Go, that this was likely to be the impact of technology-enabled transportation services such as bikesharing and carsharing. The arrival of any one option in a city is unlikely to make much of an impact, but when a full array of options exists, a tipping point is reached that allows a critical mass of people to confidently shed their private vehicles, leading to significant declines in driving.

This is especially important to understand in the context of options such as carsharing, Lyft and Uber. The arrival of these options could actually lead to a short-term increase in driving in some places, as people who had not previously had access to convenient, affordable travel by car get it. If, however, the availability of those options, when combined with other services, leads people to shed their privately owned cars – and, therefore, to buy automobility by the slice as opposed to the whole pie, as it were – the long-term reductions in driving and carbon dioxide emissions could be significant. Environmentalists and climate advocates who argue against, say, Lyft and Uber on the grounds of short-term increases in carbon dioxide emissions, therefore, could miss an opportunity to bring about truly transformative changes with large, long-term emission reduction benefits.

So yes, quantifying the carbon dioxide emission reductions caused by bikesharing systems is complicated. But we cannot make the mistake of assuming that the piece of their impact that we can readily measure is the only part that counts. Bikesharing is a key part of a “full balanced breakfast” of transportation and land-use actions – including vehicle sharing, transit, walkable land-use patterns and many more – that can enable vastly more Americans to live lifestyles that are car-light or car-free. It is only by measuring the impact on vehicle ownership that we can get the full, true picture of the contribution that bikesharing can make to the fight against global warming.