Journal of Transportation Technologies, 2012, 2, 67-74
http://dx.doi.org/10.4236/jtts.2012.21008 Published Online January 2012 (http://www.SciRP.org/journal/jtts)
Plug-In Vehicle Acceptance and Probable Utilization
Patrícia Baptista, Catarina Rolim, Carla Silva*
Department of Mechanical Engineering, IDMEC/IST-Instituto Superior Técnico,
Received November 12, 2011; revised December 10, 2011; accepted December 20, 2011
This paper presents a study undertaken to understand the plug-in vehicle acceptance and probable utilization behaviour
in terms of charging habits and utility factor (probability of driving in electrical mode). A survey was designed to be
answered via World Wide Web, throughout 3 months and only accessible to Portuguese inhabitants. The survey was
composed by biographical and car ownership info, mobility patterns, awareness toward plug-in vehicle technologies,
price premium and, finally, potential buyer’s attitudes regarding charging vehicles with electricity from the grid. An
explanation of how each vehicle technology works in the case of a regular hybrid (HEV), a plug-in hybrid (PHEV) and
a pure electric vehicle (EV) was provided. A total sample of 809 volunteers answered the survey, aged above 18 years
old, 50% male and 50% female. The results allowed the estimation o f the typical daily driving distance, the Utility Fac-
tor curve for plug-in hybrid future users, the charging preferences for future users of pure electric or plug-in hybrid ve-
hicles and the necessary feebates to promote the market penetration of such technologies. Other correlations were also
analyzed between driving patterns, type of owned car, price premium and the willingness to buy pure electric and
plug-in hybrid vehicles. The main policy implications are that an increase of awareness campaigns is necessary if the
government intends to support the plug-in electric vehicle technology widespread and a minimum of 5000 € investment
per ton of avoided CO2 will be necessary in a year.
Keywords: Pure Electric Vehicles; Plug-In Hybrid Vehicles; Utility Factor; Frequency; Period of Recharging
The urge for energy security of supp ly, air quality impro-
vement in urban areas and carbon dioxide (CO2) emis-
sions reduction are pressing decision makers and vehicle
manufacturers to act on the road transportation sector, by
introducing more efficient vehicles in the market and
spanning the energy sources available. In this sense, it is
expected that, in the near future, the tra nspor tation sector
will face considerable changes. The market share of hy-
brid vehicles (HEV) will probably raise and, in the me-
dium-long term future, the market share of alternative
vehicle technologies such as plug-in hybrid (PHEV),
electric (EV) or fuel cell vehicles will eventually start
The European Commission regards electric vehicles as
a “very important” part of its green strategy and the Euro-
pean Parliament has even launched a resolution sup-
porting the development and innovation regarding this
issue . The Portuguese government has also been
committed to enforcing the introduction of electric vehi-
cles in Portugal by launching the Electric Mobility Plan/
“Plano de Mobilidade Eléctrica” (PME) considering that
“electric vehicles will be the next logical step from hy-
brids due to their high potential for CO2 reduction” [2,3].
The expected evolution for EV and PHEV vehicles in
Portugal, whose current light-duty fleet comprises rou-
ghly 6 million internal combustion vehicles (ca. 50% die-
sel, 50% gasoline), ranges from 8000 existing vehicles in
2012 to 150 to 200 thousand in 2020, representing 10%
of vehicle sales in 2020 according to PME. However, in
terms of actual circulating fleet percentage, these 10%
are expected in the following 10 - 15 years ahead . The
main assumptions crucial for this scenario are: further
increasing oil prices; taxation and vehicle incentives legis-
lation in Europe continues as announced; availability of
high variety of EVs and HEVs; availability of charging
infrastructure; and improvement in battery technology/
costs as expected (up to 65% reductions in battery costs
in 2020) [3 ]. Th e ann ounced incentives of the Portuguese
Government to introduce the use of EVs include the ex-
istence of 320 charging po ints by year 2010 and 1300 by
2011, no payment of vehicle acquisition and circulation
opyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL.
taxes for EVs and income taxes reductions in the acquisi-
tion of an electric car . Until the end of 2011, the first
5000 private adopters of EVs will also receive a subsidy
of 5000€ that could be added by an extra 1500€ if an old
car is scrapped. Other incentives such as reduced inter-
ests from bank credit to EVs purchase and up to 50% tax
reduction for companies that buy such vehicles are also
Several surveys have been conducted in the United
States of America (USA) regarding PHEV. Kurani ana-
lyzed the behavior of 23 drivers of converted plug-in
hybrid vehicles in order to explore how they used and
recharged their vehicles . Drivers enjoyed driving in
electric mode (but also the extended range) and the pos-
sibility of recharging the vehicle at home avoiding the
refueling stations. Another conclusion was that drivers
who have unconstrained access to an electrical outlet rec-
harge the vehicles whenever possible, disregarding elect-
In order to understand the consumer reactions to HEV
in the USA, Johnson Controls commissioned a World
Wide Web survey , with a sample of 2309 adults re-
spondents of whom 35 (2%) already owned a hybrid car,
to understand consumer sen timent regarding HEV an d to
gain insight into the challenges and opportunities for
broader market acceptance. The main reasons justifying
the use of HEV were to reduce the nation’s reliance on
foreign oil (81%), to create jobs (67%) and to reduce the
USA impact on the environment (64%). The purchase
price and fuel cost were referred as the most important
factors in buying a HEV.
Furthermore, Curtin conducted interviews with a sam-
ple of 2513 adults in the USA  to determine which
factors would facilitate sales of PHEV and which factors
would represent barriers to their successful introduction.
The most important conclusions are that, on average, the
purchase probabilities declined by 16% for each doubling
of the initial cost premium and that first time PHEV buy-
ers are likely to own their own home, have convenient
access to an electric outlet and relish the opportunity to
avoid gas stations and recharge their vehicles overnight
at off-peak pricing.
In terms of the interest of niche fleets for new tech-
nologies, Gao and Kitirattragarn  conducted a survey
to New York taxi owners to analyze the probability of a
taxi owner to buy an hybrid taxi. The authors used mo-
bility patterns and taxi fleet tu rnover rates to estimate not
only the market penetration of those hybrid taxi in a
5-year time horizon, with and without government inter-
vention, but also the respective impact on the taxi fleet
It is interesting to note that few studies discuss the real
usage of plug-in retrofitted vehicles, and that usually
surveys are used to evaluate future owner’s behaviour of
this not yet largely available vehicle technology. These
surveys are USA market oriented and focus only on HEV
and PHEV technologies. Therefore, having a European
market opinion and focusing on pure electric vehicles is
worthwhile, since the different driving patterns of both
markets are reflected in the respondent’s answers.
This paper presents the results of a survey conducted
in the World Wide Web to Portuguese inhabitants in
order to gather insight in factors such as mobility pat-
terns, relative importance of vehicle attributes, aware-
ness towards plug-in vehicle technologies (both PHEV
and EV), price premium and potential buyer’s attitudes
regarding charging vehicles with electricity from the
grid. The results allow the estimation of the typical daily
driving distance, the Utility Factor curve for PHEV fu-
ture users, the charging preferences for future users of
EV and PHEV, the necessary feebates to promote the
market penetration of such technologies and the correla-
tions between driving patterns, type of owned car, price
premium, car ownership and the willingness to buy EV
The survey methodology for the study is presented in
the following section, which is followed by survey re-
sults and statistical data analysis. A discussion follows
the survey data analysis to translate private car/future
private car owner’s acceptance of EVs and a cost/benefit
analysis including policy implications. The paper con-
cludes with th e major findings of the study.
2. Survey Methodology
The su rv ey w as d es ign ed to be ans w er ed v ia W o r ld Wi d e
Web and only accessible to Portuguese inhabitants. It
contained an explanatory table regarding the type of fuel,
vehicle range, battery recharging time (for a typical 220
V, 15 - 30 A outlet) and a small explanation regarding the
alternative vehicle technologies presented (HEV, PHEV
and EV). The first part consists on information such as
age, gender, education, residence location, years of driv-
ing license and owned car characteristics (brand, segment,
fuel and age). The second part refers to private car user
driving patterns: daily and annual driving distances, type
of road (urban, highway, rural, mix), long distance jour-
neys (distance, frequency) and parking places (ga-
rages/street, uncover/cover parking lots). The third part
focuses on the owners/future owner’s attitudes toward a
variety of attributes to be considered before purchasing a
vehicle. The different factors considered are: fuel con-
sumption, interior space, aesthetic, environmental impact,
power/acceleration time 0 - 100 km/h, price, security and
status. These factors were ranked on a 1 - 3 scale with 1
being not important and 3 being very important. The
fourth part is focused on the awareness towards HEV,
PHEV and EV technologies, their opinion regarding the
most environmentally friendly option, how much more
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL. 69
would users be willing to pay for the vehicle, and if they
would still buy it regardless of fuel prices and with elec-
tricity driving being 2 - 3 times cheaper than gasoline/
diesel driving. Finally, the last part of the survey refers to
the potential drivers of EV and/or PHEV concerning:
main location of refueling (home, work, mall, others),
choice for refueling (battery charge indicator: empty, half
charge, less than half charge), time period of refueling (7
am to 1 pm, 1 pm to 6 pm, 6 pm to 10 pm, 10 pm to 7
am), duration of refueling and perception of duration of
refueling enough fo r a certain electric autonomy.
The results are used to characterize the sample popula-
tion and draw out useful information suitable for policy
2.1. Statistical Analysis for Utility Factor
The total fuel and energy consumption rates of a PHEV
vary depending upon the distance driven. For PHEVs, the
assumption is that its operation starts in battery charge-
depleting mode (CD) and eventually changes to battery
charge-sustaining mode (CS). The total distance between
charge events determines how much of the driving is
performed in each of the two fundamental modes. In or-
der to perceive how much of the distance driven is ex-
pected to occur in CD, an utility factor (UF) derived
from daily driving statistics must be d etermined. The UF
for a distance D is calculated based on the sum of the
kilometers travelled daily by the universe R of survey
respondents, comparatively to D, and the kilometers
travelled daily by the fleet of LDV of survey respondents
(see Equation (1)).
This utility factor for the USA can be seen in Figure
11, based on 2001 National Household Travel Survey
2.2. Statistical Analysis for Charging Frequency
Besides distance, another important factor that influences
energy consumption of EV and PHEV is the charging
frequency. If the battery is charged daily and the daily
distance is less or equal to the charge depleting range,
then the battery is always fully charged at the beginning
of the daily trip. Otherwise, the battery state-of-charge
(SOC) can be as low as the charge sustaining level .
To estimate the probable charging frequency in days
(CFdays) of the universe of survey respondents who are
willing to buy an EV and/or a PHEV, the choice for re-
fueling (battery charge indicator: BIk: 5% charge, 25%
charge, 50% ch arge) will be linked with electric range—
ER (100 km for a EV, 60 km for a PHEV) and daily dis-
tance, dk, as presented in Equations (2) and (3).
with battery indicator correction factor:
3. Survey Results and Discussion
The survey was conducted in 2009 over a period of 3
months. A total of 852 individuals co mpleted the survey,
of which 809 were considered valid (mostly aged be-
tween 25 and 50). As expected, due to the nature of the
survey, the majority of the respondents lives in urban
areas and has higher education degrees. A total of 85% of
the respondents own a private car, typically a small or
family vehicle with less than 9 years and with an engine
displacement below 2 liters (33% of which below 1.4
liters). The frequency of changing car is typically below
10 years (70% of respondents that own a private car).
Concerning driving patterns, 80% of respondents that
own a car drive typically less than 50 km daily in urban
(33%) or mix (urban-highway, 44%) roadways. Respon-
dents that own a car make weekly or monthly long
roundtrip of 100 - 500 km (53%) and 500 - 1000 km
(38%). Parking at home is mainly in the street free of
charge (48% of the respondents) or in the common park-
ing of the building (31%). Parking at working place is
typically at the build ing park in g lot or in the street free of
charge (respectively, 39% and 26%).
Regarding relevant attributes when buying a car, 80%
of the respondents consider fuel consumption, price and
safety very important. Other attributes such as interior
space, aesthetic, environmental impact and power/per-
formance are only regarded as important. Status is con-
sidered not important at all for 61% of the respondents.
Regarding awareness towards HEV, PHEV and EV
technologies and willingness to buy them, results indi-
cate that typically people were aware of the HEV and EV
technologies (90%) but not of the PHEV (only 56%).
Disregarding price information, 40% of the respondents
are willing to buy a HEV, 13% a EV and 25% a PHEV.
The price premium that potential buyers are willing to
pay for these technologies is presented in Figure 1). If
fuel price information is given, with electricity driving
being 2 - 3 times cheaper than gasoline/diesel driving, EV
potential buyers increase from 13% to 57% and PHEV
buyers increase from 25% to 67%. The most environ-
mental “friendly” technology is the EVs for 66% of re-
spondents, while HEV and PHEV are equally labeled.
Regarding the potential usage of EV and/or PHEV,
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL.
Figure 1. Price Premium in euros that respondents are will-
ing to pay for an EV or PHEV.
70% of potential buyers would preferably recharge their
future vehicles at home and 58% - 63% would recharge
when the battery indicator reveals less than half charge.
The time period of 10 pm - 7 am to recharge the vehicle
is indicated by 70% - 73% of the respondents, 80%
would allow a recharging time superior or equal to 5
hours and 80% - 90% consider this period of recharging
is enough to refill the battery charge completely. Figure
2 shows the charging location and period.
3.1. Driving Patterns and Willingness to Buy an
EV or PHEV
In this subsection, the authors search for an eventual
correlation between driving patterns and willingness to
buy an EV or a PHEV. The studied variables are: daily
driving distances (see Figure 3), type of driving (urban,
highway, mix, r ural, see Figure 4) and frequen cy of long
round trips (see Figure 5).
Vehicle owners that drive daily distances below the
electric range (ER) of the vehicle show much higher pro-
babilities of purchasing such vehicles than owners that
drive distances longer than the ER. Urban and mix (ur-
ban-highway) drivers reveal a higher willingness to buy
EV and PHEV. Contrary to the expectations, the fre-
quency of long roundtrips (higher than 100 km, the ER
for EV), on a weekly, monthly or rarely basis does not
affect significantly the willingn ess to buy EV, which may
indicate that drivers didn’t think properly on recharging
issues or are willing to have two cars, one for the short
trips and other for the longer trips.
3.2. Type of Owned Car and Willingness to Buy
an EV or PHEV
In this subsection, the authors search for a correlation
between the type of owned car and the willingness to buy
an EV or a PHEV and considering as attributes fuel type
(see Figure 6), engine displacement (see Figure 7) and
vehicle age (see Figure 8).
Gasoline vehicle users show a higher probability of
buying an EV than diesel ones and the opposite is ob-
served regarding PHEV. Owners of small engine vehi-
cles (<2 liters) reflect a higher probability of buying EV
or PHEV. Owners of cars aged between 4 and 13 years
show high probability of purchasing a PHEV. However,
owners of cars aged higher than 13 years reveal higher
probability of purchasing an EV.
Figure 2. Charging location (a) and time period (b).
Figure 3. Probability of buying an EV and PHEV as a func-
tion of daily traveled distance. ER stands for Electric Range
and is 100 km for the EV and 60 km for the PHEV.
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL. 71
Figure 4. Probability of buying an EV and PHEV as a func-
tion of type of driving.
Figure 5. Probability of buying an EV and PHEV as a func-
tion of long roundtrips (>100 km) frequency.
Figure 6. Probability of buying an EV and PHEV as a func-
tion of the fuel that respondents use in their actual car.
Figure 7. Probability of buying an EV and PHEV as a func-
tion of the engine displacement that respondents have in
their actual car.
Figure 8. Probability of buying an EV and PHEV as a func-
tion of the age of respondents’ actual car.
3.3. Price Premium and Willingness to Buy an
EV or PHEV
The eventual correlation between price premium and
willingness to buy an EV or a PHEV is analyzed in Fig-
ure 9. There is a clear trend between the probability of
purchase and willingness to pay a higher price premium
for an EV and a PHEV. Once more, PHEV purchase pro-
babilities are higher than the EV ones.
3.4. Vehicle Ownership and Willingness to Buy
an EV or PHEV
Comparing the vehicle ownership with the willingness to
buy an EV or a PHEV (see Figure 10), ther e seems to be
a tendency for higher probabilities of buying an EV or
PHEV in the respondents that do not own a private car.
Again the PHEV purchase probabilities are higher than
for EV, for vehicle owners and not owners.
3.5. Utility Factor for Future PHEV Users
According to Equation (1), the utility factor (probability
of driving in pure electric mode) for the respondents of
the survey was derived. Figure 11 shows the results ob-
tained for the driving distan ce probability and for the UF
calculation, where the US curve for the UF is represented
for comparison. It is interesting to note that for the 60 km
of electric autonomy of a PHEV, the UF is 80% for the
survey respondent’s universe and only 60% for US. The
typical daily driving distance (median of the data) is 30
km as opposed to 45 km for US drivers.
3.6. Charging Frequency for Future EV and
According to Equation (2), the charging frequency for
EV is 2 days (3 if no correction is made by BI) and 1 day
for PHEV (2 if no correction is made by BI). Figure 12
shows the correspondent histogram of charging frequen-
cies in days.
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL.
These results indicate that the most probable scenario
for PHEV users is the vehicle charging on a daily basis,
which will allow taking the most advantage of electricity
driving. On the contrary, the most probable scenario for
EV users is charging every other day.
4. Cost/Benefits Analysis
A possible scenario for Portuguese government invest-
ment/CO2 benefit resultan t of the penetration of EVs and
Figure 9. Probability of buying an EV and PHEV as a func-
tion of the price premium respondents are willing to pay.
Figure 10. Probability of buying an EV and PHEV as a
function of owning or not owning a pr ivate car.
Figure 11. Histogram of charging frequencies, according to
Figure 12. Histogram of charging frequencies, according to
PHEVs in the LDV sales is presented. The Portuguese
LDV fleet has approximately 6 million vehicles (50%
diesel, 50% gasoline) with a motorization index of 550
vehicles per 1000 inhabitants. The target of around
200,000 EV and PHEV vehicles  in 2020 (considering
70% EV and 30% PHEV), with increasing sales up to
2050 as foreseen by the government, will only displace
10% of the actual LDV fleet 10 - 15 years ahead of 2020
 due to the slow fleet turnover.
4.1. Charging Habits and Infrastructure Cost
As previously noted, it is extremely important for the
respondents to have a convenient access to an electrical
outlet at the home parking, with enough power/energy
available in the time period 10 pm - 7 am (see Figure 2).
This period corresponds to the electricity cheapest rate:
0.0742 €/kWh. A reference value of 1500 €/vehicle is
assumed to represent the cost associated with vehicle
charging infrastructure .
According to the survey, respondents are willing to pay
typically up to 1000 - 3000€ of price premium. Consid-
ering the manufacturing retail prices [4,11,14], it is ex-
pected an additional cost of 8000€ for PHEV with a 60
km electricity range and 10000€ for an EV with a 100
km electric range. Therefore, the government will have
to provide feebates of up to 7000 - 9000€ per vehicle to
promote EV and PHEV penetration in the LDV fleet,
compared to the 6500 € premium it has implemented in
4.3. Avoided CO2
A PHEV with 60 km electric range has a CO2 benefit
over a typical conventional vehicle of 60 g/km at the
driving stage (Tank-to-Wheel) and for the EV (with CO2
the benefit is 134 g/km. Considering the total fuel life
cycle (Well-to-Wheel), those values would be 41 g/km
and 85 g/km for the PHEV and the EV respectively. Finally,
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL. 73
Figure 13. Cost/benefit for EV and PHEV penetration, per
kg of CO2 avoided per year.
considering the materials life-cycle of vehicle man- ufac-
the values would be 30 g/km and 70 g/km  for the
PHEV and the EV respectively. Figure 13 shows the
cost/benefit comparison corresponding to these values.
The survey’s results and cost/benefit analysis allow the
following main conclusions. The respondents of this
survey are characterized as a population that is more
likely to accept alternative vehicle technologies such as
EV and PHEV, since they have a high level of education,
live in urban areas and are aged between 25 and 50 years
old. It is interesting to note tha t people ar e aware of pure
electric technology but are not aware of plug-in hybrid
technology. However, after a brief explanation of both
technologies, the respondents preferred the PHEV over
the EV, due to the extended auton o my and fuel flexib ility.
In this sense, the authors recommend the increase of
awareness campaigns, in case the government intends to
support PHEV technology widespread in LDV fleet.
Potential buyers of EV and PHEV technologies are
extremely sensitive to fuel prices/electricity prices: if run-
ning such technologies is 2 to 3 times cheaper, then the
probability of buying those technologies more than dou-
It is interesting to note the differences in the mobility
patterns between Portugal (example of European driving)
and the US that is reflected in the d ifferent Utility Factor
curve. For the typical 60 km of electric autonomy of a
PHEV, the UF is 80% for Portuguese fleet and 60% for
US. The typical daily driving (median of the data) is 30
km in Portugal as opposed to 45 km for US drivers. The
most probable scenario for PHEV users is charging on a
daily basis, which will allow taking the most advantage
of electricity powered driving, and the most probable
scenario for EV users is charging every other day. The
recharging will preferably occur at home in the 10 pm - 7
am period, when electricity o nly costs 0.0742 €/kWh an d
valleys in the electricity lo ad curve can be filled. A policy
to legislate/enforce the availability of appropriate charg-
ers at the households should be mandatory.
In terms of vehicle purchase, the Portuguese govern-
ment will have to provide feebates of up to 7000 - 9000
€/vehicle to promote EV and PHEV penetration in the
LDV fleet. Additi onally , if no cos t is associat ed wit h cha rg-
ing infrastructure and accounting only for additional fee-
bates, a minimum of 5000€ investment per ton of avoided
CO2 in a year will be necessary.
This research work is supported by MIT-Portugal project
“Power demand estimation and power system impacts
resulting of fleet p enetration of electric/plug-in vehicles”
(FCT reference MIT-Pt/SESGI/0008/2008), and MIT—
Portugal “Assessment and Development of Integrated
Systems for Electric Vehicles” (MIT-Pt/ED AM-SMS/
0030/2008). Thanks are due to the anonymous English
reviewer that helped to improve the grammar of the ma-
 T. Madurell, J. Merkies, V. Castillo, I. Belet, A. Cancian,
M. Carvalho, et al., “Rules of Procedure on Electric Ve-
hicles,” European Parliament Motion for a Resolution,
 MEI, Vision Paper for the EU Strategic Energy Technol-
ogy Plan by Ministry of Economy and Innovation, 2007.
 MEI, Electric Mobility, Portugal—A Pioneer in Defining
a National Model by Ministry of Economy and Innova-
tion, Lisbon, 2009.
 P. Baptista, M. Tomás and C. Silva, “Plug-In Hybrid Fuel
Cell Vehicles Market Penetration Scenarios,” Interna-
tional Journal of Hydrogen Energy, Vol. 35, No. 18,
2010, pp. 10024-10030.
 Portugal Government, 2009.
 K. Kurani, R. Heffner and T. Turrentine, “Driving Plug-
in Hybrid Electric Vehicles: Reports from US Drivers of
HEVs Converted to PHEVs, Circa 2006-07,” Institute of
Transportation Studies, University of California, Davis,
 Johnson Controls Inc., Powering the United States Hybrid
Vehicle Industry, Milwaukee, 2009.
 R. Curtin, Y. Shrago and J. Mikkelsen, “Plug-In Hybrid
Electric Vehicles,” University of Michigan, Ann Arbor,
 H. Gao and V. Kitirattragarn, “Taxi OWNERS’ Buying
Preferences of Hybrid-Electric Vehicles and Their Impli-
cations for Emissions in New York City,” Transportation
Research Part A, Vol. 42, No. 8, 2008, pp. 1064-1073.
Copyright © 2012 SciRes. JTTs
P. BAPTISTA ET AL.
Copyright © 2012 SciRes. JTTs
 A. Elgowainy, A. Burnham, M. Wang, J. Molburg and A.
Rousseau, “Well-to-Wheels Energy Use and Greenhouse
Gas Emissions Analysis of Plug-In Hybrid Electric Vehi-
cles,” Center for Transportation Research, Austin, 2009.
 C. Silva, M. Ross and T. Farias, “Evaluation of Energy
Consumption, Emissions and Cost of Plug-In Hybrid Ve-
hicles,” Energy Conversion and Management, Vol. 50,
No. 7, 2009, pp. 1635-1643.
 P. Baptista, C. Silva and T. Farias, “Energy and CO2
Emissions Scenarios of Introducing New Vehicle Tech-
nologies in the Portuguese Fleet,” International Advanced
Mobility Forum, Geneve, 2010.
 K. Morrowa, D. Karnerb and J. Francfortc, “Plug-In Hy-
brid Electric Vehicle Charging Infrastructure Review,”
EERE, US Department of Energy Vehicle Technologies
Program—Advanced Vehicle Testing Activity, Washing-
ton DC, 2008.
 F. Nemry, G. Leduc and A. Muñoz, “Plug-In Hybrid and
Battery-Electric Vehicles: State of the Research and De-
velopment and Comparative Analysis of Energy and Cost
Efficiency,” European Commission, Joint Research Cen-
tre, Luxembourg, 2009.