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Chapter 4 · Impacts of Car-Sharing
resources by increased trip chaining? Do car-sharing members make fewer
auto trips and greater use of public transit? Can significant reductions in
total auto mileage be documented? Our web-based surveys of current car-
sharing members can answer these questions.
This chapter addresses these questions and others in three sections: vehicle
ownership, travel behavior changes and related impacts, and transportation
cost changes. The final section of this chapter provides a simple standard
methodology that may help car-sharing operators and their partners evalu-
ate impacts in the future.
4.2 Vehicle Ownership
Potential Impact
One of the major public benefits promoted by car-sharing operators is the
ability of their programs to reduce private vehicle ownership. By providing
access to a vehicle for occasional trips, a household may be able to give up
its car, or a second or third vehicle, whether through cost, convenience or
environmental motivations. At the workplace, car-sharing may help em-
ployees avoid driving to work, and allow businesses and cities to reduce the
size of their vehicle fleets. Car-sharing, proponents argue, should therefore
be seen as a parking demand management strategy.
Indeed, many operators have sought to explicitly link their programs to
reductions in vehicle ownership. Almost all advertise the cost savings that
could be realized from selling a car, and some offer savings calculators to
compare the costs of car-sharing and vehicle ownership (Exhibit 4-3). Some
operators have taken this a stage further. CarSharing Portland participated
in a citywide vehicle scrap program for cars that failed smog tests; the scrap-
page fee paid for the $500 security deposit that CarSharing Portland requires
from members. In Bristol, England, a promotion with the local bus operator
provided free transit passes to members who gave up their cars.
In turn, reduced vehicle ownership may mean that less residential parking
has to be provided, and allow businesses to lease fewer parking spaces. This
is primarily an issue in urban areas where parking is scarce, and the provi-
sion of new parking is expensive. Specific benefits may include:
· Improved availability of parking. This benefit may accrue par-
ticularly in older urban areas where most households are depen-
dent on curb parking (although latent demand may mean that the
spaces fill up with other autos).
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· Reduced need to construct new public parking. This may be
relevant in limited circumstances, where new public parking is
planned to serve an older residential or mixed-use neighborhood.
· Reduced parking ratios for new development. The incorporation
of car-sharing into or nearby new development allows its impact
on parking demand to be taken into account at the time that park-
ing ratios are determined.
The benefits of reduced parking provision, provided that parking availability
is maintained, are extensively documented elsewhere (for example, Millard-
Ball, 2002; Shoup, 2005). They include cost savings to developers, residents
and cities; release of land for new development or open space; and reduced
impermeable surface area leading to less stormwater runoff.
The precise cost savings will depend on the net cost of new parking provi-
sion, after parking revenue from user fees. These figures are extremely site
specific, varying with factors such as the cost of land, financing methods,
land costs (including opportunity costs), the type of parking, and the level
of charges, if any. Average monthly costs per stall in 1997 dollars, including
Exhibit 4-3 Example Cost Savings Calculators
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Chapter 4 · Impacts of Car-Sharing
land, construction, design, contingency and operating costs, are typically
$68 for surface parking, $135 for above-ground structures and $240 for
below-ground facilities (Kuzmyak et al., 2003).2 Shoup (2005) calculates
that each parking space at the University of California-Los Angeles costs
at least $127 per month in capital and operating costs, plus external costs
of at least $117.
In major metropolitan areas where most car-sharing programs are located,
these costs are likely to be significantly higher. In San Francisco, for ex-
ample, a parking space adds $20,000-$30,000 to the cost of each housing
unit upwards of $50,000 in some parts of the city (San Francisco Planning
Department, 2002). This equates to a monthly cost of $480, assuming a 24-
year service life, a 9% interest rate and $50 in monthly operating costs. In
Palo Alto and San Jose, CA, new parking structures have been built at a cost
of more than $50,000 per space (Shoup, 2005).
There will not be a 1:1 relationship, however, between the number of ve-
hicles given up by car-sharing members, and the number of parking spaces
saved. Firstly, for existing residential developments, the effect depends on
whether the freed-up spaces are available for other users for example, if
curb parking is predominant, or if the parking is physically "unbundled"
from the unit. If each unit has separate, reserved off-street parking spaces,
such as an attached garage that is difficult to rent to other users, the impacts
of car-sharing may be more limited.
Secondly, the impacts of car-sharing on parking ratios in new development
will depend on the ability and willingness of the developer to take advan-
tage of the opportunity. In many instances, constraints may be imposed by
minimum parking requirements levied by the local jurisdiction, the require-
ments of lenders, or market preferences.
The impact of car-sharing on residential parking demand has received the
most attention. However, car-sharing also has the potential to reduce the
need for parking at the non-residential end of the trip, such as at workplaces
and stores. To some extent, these impacts will be indirect and depend on the
extent to which car-sharing is able to reduce vehicle travel, as discussed in the
following section. For example, if customers walk or take transit rather than
driving to a store or leisure facility, fewer parking spaces will be required.
However, there may be significant direct impacts if an employer is able to
2. Capital costs are amortized over a 24-year service life at a 9% interest rate.
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downsize or eliminate a vehicle fleet through joining a car-sharing program,
or if car-sharing is introduced as an employee trip reduction strategy. These
types of programs are discussed in detail in Section 5.7.
Empirical Evidence
Impacts on vehicle ownership have been a relatively simple area to explore
in methodological terms and have been the subject of a large number of
studies. Typically, the impact is calculated as follows:
% members who give up a car3* members per car-sharing vehicle 1 = vehicles reduced
As shown in Exhibit 4-4, an average of 21% of members give up a vehicle after
joining a car-sharing program. This figure is similar both in North America
(21%) and Europe (22%). Fewer studies provide data on vehicle: member
ratios. However, assuming a ratio of 1:27 (an assumption discussed later in
this chapter), this equates to each car-sharing vehicle replacing five to six
privately owned vehicles, or a net reduction of four or five.
Some studies credit a reduction in vehicle ownership for members who state
they avoided buying a car as a result of joining the car-sharing program.
While this is certainly the case for many members, this form of survey ques-
tion is more speculative and is likely to overstate the overall impacts. On
average, 34% of members state that they avoid buying a car, with figures as
high as 77% (Exhibit 4-4).
In contrast, one study that used a control group methodology suggests that
just 4% of members avoided purchasing a vehicle (Cervero & Tsai, 2003).
This is calculated as the difference between the number of members and
non-member controls who purchased a vehicle (Exhibit 4-5). This control
group methodology is subject to several limitations and may not be repre-
sentative, and may therefore understate this figure,4 but it does suggest that
the true value lies somewhere in between.
3. Note that some studies report the number of members who give up a car as a percentage of those who owned a vehicle before joining
the program. Properly, this should be expressed as a percentage of total members, in order to keep units consistent with "members per car-
sharing vehicle."
4. The control group was originally designed to consist of non-members with similar motivation levels, interest and ideological leanings to
members. Control group members had registered to join City CarShare, but had not actually joined for example, because a pod was not located
close to them (Cervero & Tsai, 2003). By the time of the later surveys, however, City CarShare had expanded to cover most of San Francisco,
and there may have been other reasons for control group members not to join such as finding that they could do without a car altogether. In
addition, the control group sample size was small, with just 54 responses to this survey.
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Chapter 4 · Impacts of Car-Sharing
Exhibit 4-4 Impacts on Vehicle Ownership
% of Respondents Who Have... Vehicle Ownership Before Joining
Given Up Members Private
a Vehicle Forgone Per Car- Vehicles
(primary or Purchase of Sharing Replaced per One or Sample
Reference Region second) a Vehicle Vehicle Shared Car** None More Size Comments
EUROPEAN STUDIES
Wagner (1990) Switzerland 26%
Hauke (1993) Bremen 42% 16%
Baum & Pesch (1994) Germany 23% 32%
Krietemeyer (1997) Munich 19% 34% 596
Lightfoot (1997) Netherlands 44%
Meijkamp & Theunissen (1997) Netherlands 17% 5%
Perner, Schöne & Brosig (2000) Dresden 10% 28% 318
Cambio, unpublished survey Bremen, Aachen & Cologne 21% 11% Cited in Koch (2002)
Olsen & Rettig (2000) Denmark 7% 26-35% 14 1.0 57% 43% Further 31% gave up a car
independent of car-sharing
Hope (2001) Edinburgh 32% 16 5.1 42% 58% 38
Koch (2002) Bremen 9% 26% Figures refer to members with
combined car-sharing/annual
transit pass.
Holm & Eberstein (2002) Dresden 10% 21% 35 3.5
Krietemeyer (2003) Munich 12% 35% 700
Rydén & Morin (2005) Bremen 34% 17% 19 6.5 301
Rydén & Morin (2005) Belgium 21% 14% 18 3.8 272
European Average 22% 22% 20 4.0 50% 51% 371
NORTH AMERICAN STUDIES
Cambridge Systematics (1986) San Francisco, CA 12% 43% 11 1.4 122 Assumes 1.9 individual users per
household
Robert (2000) Montreal, QC 21% 61% 17 3.5 49% 52% 153
Robert (2000) Quebec City, QC 29% 56% 17 4.7 38% 63% 208
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Exhibit 4-4 Impacts on Vehicle Ownership (cont'd)
% of Respondents Who Have... Vehicle Ownership Before Joining
Given Up Members Private
a Vehicle Forgone Per Car- Vehicles
(primary or Purchase of Sharing Replaced per One or Sample
Reference Region second) a Vehicle Vehicle Shared Car** None More Size Comments
Katzev (1999), Katzev, Brook & Portland, OR 26% 53% 13 3.5 59% 41% 64
Nice (2000)
Cooper, Howes & Mye (2000) Portland, OR 23% 25% 89
Zipcar (2001) Boston, MA and 15% 35% 20 3.0 Details of methodology not available
Washington, DC
Flexcar (2001) Seattle, WA 6% Cited in Vance (2004). Figures refer to net
change in vehicle ownership, with 15%
giving up a vehicle and 9% adding a new
vehicle to the household.
Jensen (2001) Vancouver, BC 28% 57% 18 5.0 86% 14% 370 Figures refer to those who gave up a vehicle
0-6 months before joining CAN. Figures for
"forgone purchase" exclude "don't know"
responses.
City CarShare (2002) San Francisco Bay 20% 63% 25 5.0 65% 35% 130 Excludes those who did not give an answer
Area, CA
Flexcar, unpublished survey Washington, DC * 42% 53 67% 33% Details of methodology not available
Cervero & Tsai (2003) San Francisco, CA 24% 4% 25 6.0 Figures refer to net change in vehicle
ownership per member (-0.24) and per
non-member control (+0.04). Source for
members per vehicle is City CarShare.
Vance, Williams & Rutherford Seattle, WA 15% 40% 48 Figures refer to net change in vehicle
(2004) ownership, with 23% giving up a vehicle
and 8.5% adding a new vehicle to the
household.
AutoShare, email Toronto, ON 15% 25% 22 3.3 Details of methodology not available
Communato (2004) Quebec (4 cities) 32% 77% 20 6.4 2167
Lane (2005) Philadelphia, PA 21% 44% 23 4.7
North American Average 20% 41% 24 5 61% 40% 372
Combined Average 21% 34% 23 4.5 58% 42% 372
*25% of members who do own cars have sold or are considering selling their car.
** Excluding impacts of forgone purchases.
Many surveys do not distinguish between respondents who have given up a car because of car-sharing, or for some other means. Where available, the data in the table refer to those who have given it up because of car-sharing.
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Chapter 4 · Impacts of Car-Sharing
Exhibit 4-5 Change in Household Vehicle Ownership
San Francisco City CarShare
Members Non- Difference
Change in Vehicle Ownership (A) Members (B) (A-B)
Reduced by Two or More 2.5% 0 2.5%
Reduced by One 26.6% 8.0% 18.6%
Did Not Change 63.2% 80.0% -16.8%
Increased by One 7.2% 12.0% -4.8%
Increased by Two or More 0.4% 9.0% 0.4%
Source: Cervero & Tsai (2003). Figures refer to change in household motor vehicle ownership within the
first two years of the San Francisco City CarShare program.
In the web-based survey of current car-sharing members, conducted for this
study in 2004, all but one of the major car-sharing companies in the United
States and Canada encouraged their members to participate in this survey
by connecting to a specific website. A total of 1,340 complete and valid
responses were received, representing an 11% response rate (see Chapter 3
for details of survey methodology). In this survey, respondents reported the
following results of their car-sharing membership as shown in Exhibit 4-6.
Exhibit 4-6 Effects of Car-Sharing Membership on Auto Ownership
Neither
agree nor Strongly
Effect disagree Agree agree
Was able to sell my car 59.9% 3.9% 7.4%
Was able to sell the family's second car 26.5% 32.1% 17.5%
Postponed buying another car 16.6% 39.1% 31.4%
Source: Car-Sharing Member Survey.
The strongest impact in these results is the delay in purchasing another car,
reported by 70.5% of all respondents who agreed or strongly agreed that they
were able to postpone buying a car because of their participation in car-shar-
ing. Not to be overlooked is the nearly 50% of all respondents who reported
that they were able to sell their second car because they were involved in
car-sharing. In total, 55.2% of the respondents agreed or strongly agreed
that they were able to sell their car, the family's second car, or both.
As discussed earlier in this section, the net reduction in vehicle ownership
per car-sharing vehicle depends not only on the percentage of members who
give up a car, but also on the vehicle: member ratio of car-sharing organiza-
tions. Based on data from Shaheen (personal communication), the vehicle:
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member ratio in December 2004 was 1:66 in the United States, and 1:20 in
Canada. The US ratio has shown a substantial decrease in recent years,
influenced by two key trends:
· Many of the reported members are likely to be inactive or lapsed
members. Promotional incentives and changes in pricing policy
mean that many of these individuals did not have to pay an appli-
cation or renewal fee; they use the car-sharing service occasionally
or not at all.
· The increase in the business market means that many members
are employee members, who primarily use car-sharing at the
workplace during the day. The primary environmental objective
for this market segment is to help them avoid driving to work,
rather than to allow them to give up a vehicle.
The web-based survey for this project was distributed by car-sharing opera-
tors to their members via e-mail lists or newsletters. The researchers believe
that respondents are representative of those who received the survey, and
that they are more likely to represent the active, individual members who are
included on these e-mail lists. (Because only 9.5% of respondents reported
that their employer paid all or part of their car-sharing costs, we conclude
that the respondents better represent individual members than corporate
or other members.)
This means that it is inappropriate to apply the 1:66 vehicle:member ratio to
the 55% of respondents who reported giving up a car. Instead, a 1:27 ratio is
used, which represents the vehicle: member ratio in the United States in 2002
(Shaheen, Schwartz & Wipyewski, 2004). The 1:27 ratio represents a good
estimate of the ratio of vehicles to active, individual car-sharing members,
given that the promotional incentives and pricing structures noted above
were less prevalent in 2002; and that business usage comprised a much
smaller segment of the market; although it may be a slight underestimate
given continuing efforts by car-sharing operators to improve efficiency and
increase utilization. The 1:27 ratio is also consistent with the studies reported
in Exhibit 4-4.
Applying this ratio means that each car-sharing vehicle is estimated to
take 14.9 private cars off the road a net reduction of 13.9 vehicles. Ap-
plied to the entire US fleet of 939 car-sharing vehicles in December 2004, the
estimate yields a net reduction of more than 13,000 cars. If members who
reported delaying the purchase of a vehicle are included, the net reduction
is substantially greater.
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Chapter 4 · Impacts of Car-Sharing
A total decline of more than 13,000 cars might indeed be large enough to cre-
ate a noticeable impact on auto ownership and traffic in the neighborhoods
where these individuals lived. We can say that these numbers represent a
minimum number of autos taken off the streets, because those persons who
sold more than one car as a result of car-sharing membership should prob-
ably be added to these calculations. Unfortunately, data from the internet
survey do not allow us to precisely calculate the numbers of cars sold.
Persons who reported being able to sell their own car still tended to have
access to another car in the household. They also more often tended to be
living with someone else, male, and in the upper income brackets (over
$100,000 per year).
Those who reported that they were able to sell the household's second car
more often tended to have lower annual incomes (below $20,000) and not
upper incomes (above $125,000). They were also more often female, not car
owners, and less than 34 years of age and not over 45.
Those who reported that they postponed buying another car more often
tended to have lower annual incomes (below $30,000) and not upper incomes
(above $125,000). They also tended to be younger (under age 34) and not
in the 55 to 64 age bracket.
These results are surprising in several ways. Firstly, they suggest far more
dramatic impacts on vehicle ownership than previous studies. As shown
in Exhibit 4-5, previous studies indicate that around 20% of car-sharing
members sell a car. Exhibit 4-6 suggests that the percentage may lie at more
than 50%, with by far the greatest impact being on second car ownership.
Meanwhile, 70% of members have been able to postpone buying a car again,
far greater than the figure suggested by previous studies.
One possibility is that the long-standing nature of the car-sharing members
responding to the survey on average, they had been members for 19.5
months has allowed greater time for these impacts to become evident. Al-
ternatively, it could indicate that car-sharing operators are targeting second
car owners rather than car-free households as the market matures beyond
the early adopters. Note that other, recent studies have also suggested ve-
hicle ownership impacts of greater magnitude than previous research. Lane
(2005), for example, reports that each PhillyCarShare vehicle removes an
average of 22.8 cars from the roads 10.8 cars from members who give up
a car, plus 12.0 cars from members who avoid purchasing a vehicle. Often,
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