Thousands of young urban students and professionals chose homes to be close to work, school or transit, and commute, shop, and play mostly by transit, bicycling or walking. Additionally, there are thousands of households which, due to issues of affordability, have fewer vehicles than workers, or have no vehicles at all. On the other hand, there are also many households with extra vehicles which are hardly used. For all of these situations, “car-sharing” – the idea of having access to a car and paying for it only when you need it – provides a suitable option. For young professionals, it can improve mobility on those occasions when a car is needed, when in the past a car would have been rented or borrowed. Similarly, for low income households, it can add mobility at important times when other options are too time-consuming or inconvenient. For households with extra vehicles, selling the vehicle and car-sharing instead can eliminate the costs of ownership for the little-used vehicle.

For all of these reasons and more, car-sharing has taken off in many major U.S. cities. By now, residents in major metropolitan areas probably took notice of the strangely painted shared-car vehicles zipping around. As of 2005, there were 28 car-share systems in 36 cities in North America, with a total membership of over 75,000, and a total shared fleet of over 1100 vehicles. [1] Commercial car-sharing began in Europe in the 1980s and came to the U.S. around 1994. [1]

They all work along similar lines: the car-share operator owns and maintains a fleet of cars, the scheduling system, website, etc. The cars are placed in special, reserved parking spots in various locations in the city. Anyone can become a car-share member (with certain restrictions for those under 21). Members can use any car in the system, as long as it is available. They can check availability of any car by phone or internet and reserve the car at the location for the time frame they desire. Members have a universal key which opens and activates any car in the system. During their reservation period, they can use the car as much as they please. They can extend their reservation during use by phone or internet, as long as the car hasn’t been reserved immediately afterwards by another member. At the end of the month, the member is billed for their use, plus small monthly membership fees, if any. There are certain restrictions that help things run more smoothly; the hefty penalty for a late return helps ensure that users plan realistic reservation times and don’t leave the next user waiting.

Each system has a different system of rates. One local Bay Area operator charges 44 cents per mile and four dollars per hour during the day, or two dollars per hour at night. Another operator charges 8 dollars per hour with no charge for mileage. Some operators offer various types of vehicles and might charge different rates for each vehicle. A number of operators offer car-sharing and compete head-to-head in the different cities, placing competing vehicles right next to each other in a parking lot.

Because car-sharing has the potential to reduce automobile ownership for some, meanwhile increasing access to automobiles for others, the impact of car-sharing on urban travel and the environment is difficult to unravel. Professor Robert Cervero and a team of researchers and students have been working to understand these relationships for the past five years, supported by a Value Pricing Demonstration Grant from the U.S. Department of Transportation. Planning for the opening of City CarShare, a non-profit car-share operator in San Francisco, the team took a longitudinal approach. They tracked a group of car-share members and “non-members” over four years, beginning before the opening of the program, in order to reveal the impacts of car-sharing on travel consumption and vehicle ownership and make strong statements about the impacts of car-sharing.

Those who signed up to immediately join the program formed the “member” group, while those signing up to one day become active members functioned as the “non-member” control group. These non-members were ideal controls because they displayed comparable levels of motivation and interest, having taken the time to sign up for the program, but had not formally joined due to factors like there not being shared vehicles in their neighborhood. The first set of surveys was conducted several weeks before City CarShare’s March, 2001 inauguration. Similar surveys were then conducted of both groups three months, nine months, and two years into the program. The fifth and final set of surveys was conducted in May of 2005. As a result, the research team reached some main conclusions of the work and important implications for urban transportation policy, beginning with trends in car-share usage among members, followed by comparisons between members and non-members.

From the initial March 2001 opening in San Francisco in early to mid-2005, City CarShare grew tremendously. The number of points-of-departure (PODs) grew from 6 to 43, and the number of shared vehicles grew from 12 to 87. Part of this expansion resulted from the introduction of the program to Berkeley and Oakland in 2003. Active membership in City CarShare has trended upwards from over 1800 in September 2002 to 3800 in May 2005. The monthly average number of reservations grew from less than a thousand during the first year to well over 5000 by mid-2005. Members logged 106,000 miles in CarShare vehicles in the month of May, 2005.

The most common purpose for car-sharing was shopping, followed by social-recreational travel and personal business, with work trips constituting only around 10% of car-share trips. Around two-thirds of CarShare trips were made by the driver alone, with no passengers. The highest vehicle occupancies were for trips to school (nearly 2 persons), and the least discretionary trips were made mainly by solo-drivers. CarShare users were asked what modes they would have otherwise taken had car-sharing not been available. Interestingly, respondents claimed that 30% of trips would likely not have been made. For trips that would have been made, car-sharing draws more trips from public transit than any other modal option. To access shared cars, most walked (78%), took transit (14%), or biked (6%).

Looking at overall travel patterns, car-sharing made up 4.8% of members’ total daily trips, up from 2.2% three months into the program but down from 8.1% at the nine-month mark. Adjusting for trip length, car-sharing made up 5.4% of total vehicle miles travelled (VMT) by members. The overall most popular form of conveyance by members – representing 47.6% of all trips – was “non-motorized” (i.e., walking or cycling). Non-members were twice as likely to use a private car, and significantly less likely to take transit, compared to members. Members generally took “green modes” to work or school: nearly 90% of their journeys to work or school were by public transit, foot, or bicycle – a far higher share than for non-members. Members and non-members also differed in how they made shopping, social, and personal business trips, with members more likely to take transit or non-motorized modes. Most members and non-members have a transit pass, own a bicycle and many clearly have options for private car travel. Non-members were slightly more likely than members to have off-street parking (56% versus 41%).

City CarShare’s first wave of members were found to be fairly unrepresentative of the Bay Area’s and even San Francisco’s population, drawn disproportionately from professional-class residents who did not own cars and who lived either alone or in non-traditional households. This pattern generally held four years after City CarShare’s inception. In 2005, whites made up 82.8% of surveyed members (considerably above the 49.6% and 48.8% share for San Francisco and Alameda County, respectively). Members’ median annual personal income of $58,150 was above the census averages for San Francisco as well as the East Bay. Car-share membership also ran in the family: 32.6% of surveyed members’ reported another City CarShare member in the household.

In 2005, 62.8% of members were from zero-vehicle households and 28.7% were from one-vehicle households. Thus, 91.5% were from 0-1 vehicle households – above the 83.3% share during the program’s first year and well above the average of 70.6% for all San Francisco households. Members were half as likely as non-members to have acquired a vehicle, and about as likely to have reduced car ownership since 2001. Consequently, for every 100 member households, about 7 net vehicles were shed, while for every 100 non-member households, about 3 net vehicles were added during the period.

Compared to the first survey (“pre-car-share” — February 2001) and the fourth survey (“second anniversary” – March 2003), mean daily travel distances of City CarShare members fell slightly by the 2005 survey. For non-members, they rose over the long-term but largely stabilized over the 2003-2005 period. None of these changes, however, were statistically significant. Mean travel times steadily fell for both groups over the three survey periods, although more rapidly for non-members. Average travel speeds rose markedly among members, in part from the substitution of City CarShare trips for travel formerly by foot, bicycle and transit. In effect, car-sharing has enhanced mobility, allowing members to conveniently reach more destinations in and around San Francisco.

During City CarShare’s first two years, average daily travel (VMT) fell slightly for members yet increased for non-members. In order to understand differences in the mix of modes and occupancy of the vehicles by members and non-members, we adjusted the mileage to make a Mode-adjusted-VMT (MVMT). For example, a mile by transit or carpool was discounted compared to a mile as a solo driver because of the differences in environmental impacts. For members, MVMT fell by 67% over the long term (2001 to 2005) and by 38% over the intermediate term (2003 to 2005). Such declines were a combination of not only shifts to “green modes” and shorter travel, but also relatively high occupancy levels for private car trips, including those in City CarShare vehicles. MVMT for non-members rose in the first two years but like with members, appear to have fallen some since 2003.

Accounting for the differences in fuel economies among personal cars used by members and non-members, as well as the shared cars (which include mostly small cars and hybrids), members’ average daily fuel consumption fell steadily during the program’s first four years. This likely reflected a combination of members reducing private car ownership, switching to more fuel-efficient City CarShare vehicles, and carrying passengers for many car-share trips. By comparison, mean fuel consumption rose among non-members during the first two survey periods and fell during the 2003-2005 period.

Before and after comparisons from the first four years of the City CarShare program reveal declines in travel consumption among members compared to non-members. While most of these declines attributable to car-sharing accrued during the first several years in recent years levels of travel suppression appear to have stabilized or perhaps slightly reversed themselves. This makes sense – a typical member can only reduce travel so much. Though averages level off, as membership grows, the total impact of car-sharing continues to grow accordingly.

A statistical model of car ownership shows that membership in City CarShare and living near a POD significantly increases the likelihood that an individual lives in a car-free household. In a model of changes in car ownership, member status significantly predicts a reduction in car ownership during the period from 2001 to 2005. Similarly, having a transit pass and having at least one POD near one’s residence were both associated with net declines in household cars. Overall, members were half as likely as non-members to have acquired a vehicle during the 2001 to 2005 period and about equally as likely to have reduced car ownership since 2001. In essence, for every 100 member households, about 7 vehicles were shed, while for every 100 non-member households about 3 vehicles were added during the period. A statistical model of the choice of using car-sharing or otherwise for a trip revealed that members were less likely to choose car-sharing for work trips and that car-sharing decreased with increasing numbers of vehicles owned per household member. In this light, car-sharing is seen to be self-reinforcing: it facilitates the reduction in the number of private vehicles in the household, which in turn induces more car-share use.

Statistical models showed that City CarShare membership was associated with a reduction in daily VMT after controlling for respondents’ socio-economic characteristics. All else being equal, City CarShare membership predicted lowered daily travel by 7 vehicle miles (equal to about 1/3 gallon of gas per day per member). Additionally, the model showed that residing in San Francisco (compared to the East Bay) predicted a reduction in travel by 3 miles, owning a bicycle cut travel an additional 4 miles, while on the other hand, every additional car owned per household member raised daily VMT by 13 miles. The combination of being a City CarShare member, owning a bicycle, and reducing car ownership all serve to shrink a household’s ecological footprint in the San Francisco Bay Area. Increasing the net impact of car-sharing can only be achieved by adding more members.

Based on the five surveys of City CarShare members and non-members, there is clear evidence of sustained net reductions in car-share members’ VMT and fuel consumption some four years into the City CarShare program, due mainly to shorter, higher occupancy, and reduced private car travel during the first several years of the program. In relative terms, the biggest long-term environmental benefits of car-sharing in the San Francisco Bay Area came from reduced gasoline consumption, followed by VMT reductions, and reduced travel distances. Car-share members’ propensities to walk, bike, take public transit, and when they drive, to have other occupants in the vehicle, largely account for these sustained benefits. Reduced travel was matched by increased accessibility afforded to those who joined City CarShare. Rising personal benefits matched by declining social costs (declining VMT, fuel consumption, vehicle ownership) suggests car-sharing is a “win-win” proposition – benefiting users and non-users alike.

The circularity between car-share membership and car-shedding is not unlike that of car ownership and induced travel. Membership was associated with reduced car ownership, and reduced car ownership was associated with more car-share travel. It was not just average VMT that fell among members relative to non-members. Because car-share vehicles tend to be small, fuel-efficient, and carry several people, per capita levels of gasoline consumption and accordingly greenhouse gas emissions have also trended downwards. Mindful of the cumulative costs of driving, car-share members, we believe, have also become more judicious and selective when deciding whether to use a car, take public transit, walk, bike, or even forgo a trip.

These results point to important implications for larger urban planning issues. Car-sharing could become an important component to improving mobility for low-income families, without the heavy burden of vehicle ownership costs. It could also delay or reduce the acquisition of vehicles by young urban residents who may have growing mobility needs as incomes rise. There are also important synergies with urban development to consider. While infill and transit oriented developments are growing in importance in most metropolitan areas in the country, pressures remain on developers to supply parking at traditionally high rates, reducing the cost effectiveness and profitability of potential projects. Car-sharing has been shown to reduce vehicle ownership rates among members, and may become an important element to infill proposals with lower parking to unit ratios. Indeed, at least one large housing project in San Francisco house City CarShare vehicles in exchange for lower parking requirements. Furthermore, project proposals involving car-sharing may strengthen their case for approval because it can be shown that car-share users tend to travel more judiciously and reduce their negative traffic impacts.

For all of these reasons and more, car-sharing is growing beyond just a niche and becoming a common site across the country. And with further urban infill development, rising gas prices, and growing environmental concerns, the market potential is likely to grow. And with that growth comes lower parking pressures, traffic, fuel use and improved travel options for households with a wide range of travel needs.