Title: Travel to work in Dublin. The potential impacts of electric vehicles on climate change and urban
air quality.
Authors: John Brady*, Margaret O‘Mahony
*Corresponding Author
Tel: +353 18932537
E-mail address: bradyj7@tcd.ie
Address: Centre for Transportation Research, Simon and Perry Building, Trinity College, Dublin 2,
Ireland.
Keywords: Electric vehicles, Urban air quality, Greenhouse gases.
Abstract
The Irish government has outlined plans for 10% of the national road fleet to be powered by electricity
by 2020. The objective of this paper is to evaluate the potential reduction in road traffic related
emissions due to commuting in the Greater Dublin Area (GDA) under different electric vehicle market
penetration scenarios. The results indicate that the introduction of electric vehicles offers the potential
for reductions in all road traffic related emissions. However, the time required for electric vehicles to
acquire a significant share of the fleet, suggests that they will have a limited impact on climate change
and urban air quality for at least the next decade.
1. Introduction
In November 2008, the Minister for transport in Ireland announced a government target for 10%
(230,000 vehicles) of the private car fleet to be powered by electricity by 2020 (Dempsey, 2008). The
imminent commercial deployment of electric vehicles (EV) has the potential to address issues such as
climate change, oil dependence and air quality. Research suggests that typical commuter profiles are
particularly suited to EVs due to the repetitive nature, fixed distances of the trips and because
vehicles are available for recharging either during daytime or overnight (Turrentine et al., 1992).
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In 2008, transport emissions in Ireland accounted for 21.3% (14,255 MtCO
2eq
) of the national total,
which represents an increase of 176% on 1990 levels (EPA, 2009a). This upsurge can be attributed
to a period of unprecedented economic growth, which led to an increase in vehicle numbers, the
purchase of larger vehicles and the reliance on private cars for commuting to and from work
(EPA, 2009). Employment and household incomes have also increased significantly in Ireland over
the last decade. This has subsequently led to a substantial increase in the level of car dependence
and private car registrations in the country. These trends are particularly noticeable in the Greater
Dublin Area (GDA), which saw an increase in employment by 48.9% and private car registrations by
over 60% over the period 1996-2006 (Central Statistics Office, 2007a). The GDA is defined as Dublin
City and the surrounding counties of Fingal, Dun Laoghaire-Rathdown, South Dublin, Kildare,
Wicklow and Meath. Furthermore, in 2006, 51.8% of commuters in the GDA travelled to work by car,
an increase of 5% on 1996 levels (Commins & Nolan, 2008). Morgenroth (2001) utilized data
supplied by the Irish Revenue Commissioners to estimate the extent of the commuting belt around
Dublin and concluded that in fact the commuter belt extends beyond the GDA and that a substantial
number of individuals commute long distances from counties outside the GDA. This is referred to as
the
“
Outer
Belt” region in Figure 1.
Insert Figure 1 here.
Figure 1. Commuter Belt for Dublin City. Source Morgenrath (2001).
In scientific literature many studies have explored the benefits of EVs and report that a net reduction
in greenhouse (GHG) emissions can be achieved by replacing internal combustion engine vehicles
(ICEV) with EVs. The Electrical Power Research Institute (EPRI) and the Natural Resources Defence
Council (NRDC) compared plug-in hybrid vehicles (PHEV) to hybrid vehicles (HEV) and ICEVS using
specific electricity generating technologies. The results concluded that regardless of the
electricit
y
supply, PHEVs and HEVs would result in a net decrease in GHG emissions (between 28-67%)
relative to ICEVs (EPRI, 2007). Litienthal and Brown (2007) estimated the potential carbon dioxide
(CO
2
) emissions reduction through the introduction of PHEVs into individual states in North America. It
was determined that use of PHEVs would provide CO
2
emissions reductions in 49 states and on
average a CO
2
reduction of 42% per mile driven. However, the author note that majority of the U.S
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electrical generation comes from coal, which implies that greater reductions would be possible if a
higher proportion of the fuel mix came from renewable sources. In the Irish context, Smith (2010)
examined the potential benefits of PHEVs in terms of reducing the primary energy requirement (PER)
and CO
2
emissions of passenger cars in Ireland. The analysis found that the electricification of the
Irish passenger car fleet could reduce the PER and CO
2
emissions by 50% for each km travelled in
electric mode.
2. Data and Methodology
2.1 Fleet emission calculation
The details of regular work trips were sourced from the Place of work Census of Anonymised Records
(POWCAR) (Central Statistics Office, 2007b). It derives from the data gathered in the 2006 Irish
census and details information on 1,834,472 regular work trips of the entire population. It is the only
source of disaggregate origin-destination travel to work data in Ireland.
The ISus private car stock model, developed by the Economic and Social Research Institute (ESRI) of
Ireland (Hennessy and Tol, 2010), was used to make assumptions about the future composition of the
private car fleet. The model, which is driven by forecasts on the economy and the population is
constructed from a long history on passenger car sales, which has been calibrated to recent data on
the actual stock (Hennessy and Tol, 2010). The model distinguishes cars by fuel type, engine size
and age. The current composition of the Irish private car fleet in terms of diesel/gasoline, percentage
weight and engine size distribution is presented in Table 1.
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Table 1. Current Irish private car fleet composition.
Engine Size (L) Fuel # Vehicles % Total private car fleet
<1.4
Gasoline 963,044
49.9
1.4-2.0 543,080
28.1
>2.0
53,251
2.8
<2.0
Diesel 320,073
16.6
>2.0
50,571
2.6
Total
1,930,019
100
The potential reduction in tailpipe GHG emissions was calculated using the COPERT 4 computer
model. The COPERT 4 model is part of the EMEP/CORINAIR Atmospheric Emissions Inventory
Guidebook (AEIG) and is recommended by the European Environment Agency (EEA) to calculate
national emission inventories (Kousoulidou et al., 2008). Over twenty European member states
including Ireland use the COPERT 4 model.
The COPERT 4 methodology is based on average speeds and corresponding average speed
emission factors to calculate vehicle emissions (Gkatzoflias et al., 2007). It includes a total of 37
different classes of gasoline passenger cars. A given car belongs to one of three different
―
subsectors
depending on the cylinder volume (<1.4 litre , 1.4–2.0 litre and >2.0 litre), and each
subsector contains 12–14 different
―tec
hnology classes
,
reflecting the various stages of the EU
exhaust regulation (e.g. EURO 1, EURO 2 etc.). For diesel passenger cars there are two different
subsectors (<2.0 litre and >2.0 litre), each containing seven different technology classes. A mix of
urban (14% of total distance), rural (9% of total distance) and highway (76% of total distance) driving
was considered with average speeds of 40 km/hr (rural), 60 km/hr (urban) and 100 km/hr (highway).
The vehicles were allocated to different European emission standards on the basis of their age and
application dates of the standards in Ireland.
The temperature data required for the COPERT models was sourced from the European Climate
Assessment & Dataset (ECA&D, 2010). For the period 2006-2008, the 2005 advanced fuel
specification provided by COPERT 4 was used. However, for the period 2009-2020, despite there
being an advanced fuel specification provided by COPERT 4 for 2009 stage fuel, the fuel
4
specifications which are defined in the Air Pollution Act 1987 were utilized instead
(Irish Statue Book, 2003). The only difference being that the 2009 stage fuel specifications, has a
reduced sulphur content from 50 parts per million (ppm) to 10 ppm. The polycyclic aromatic
hydrocarbon value given in the Irish Statutes is in % m/m, and not in % v/v as demanded by COPERT
4, so the default figure was used instead.
3.2 Employment and Passenger Car kilometres (PCkm) in the GDA
In 2006, it is estimated that 223,578 individuals travelled to work in Dublin by car. Based on the
Central Statistics Office (CSO) employment statistics for the nation over the period 2006-2009
(Central Statistics Office, 2010) and future employment projections by the ESRI (Bergin et al., 2010),
the number of individuals who will potentially travel to work by car to Dublin in 2020 was forecast.
Under a low growth scenario, the ESRI predict that annual employment will increase by 1.9% and
0.9% over the periods 2011-2015 and 2015-2020 respectively. By applying the national employment
statistics to the GDA, we estimate that approximately 226,300 individuals will travel to work by car to
Dublin in 2020, of which approximately 156,800 will belong to households with two or more cars.
As this paper is concerned with annual emissions, the daily trip kilometres are calculated on an
annual level, assuming that an individual completes a daily return work trip in a 220 day year. The
average distance travelled to work in Dublin was 15.3 km in 2006, which equates to an average
annual distance of 6,732 km per individual.
3.3 Potential electric vehicle market penetration
The main uncertainty of the study is without any doubt the estimation of the future market penetration
of EVs into the motor industry. The accurate prediction of market penetration includes great
uncertainties and depends on a multitude of influencing factors (i.e. fossil fuel price, national incentive
schemes and new developments in EV technology). In this study the rate of market penetration was
estimated using a logistic S-curve. This methodology is in keeping with other studies, which have
used S-curves to predict the market penetration of new technologies. These include
Draper et al. (2008), who employed S-curves to predict the economic impact of EV adoption in the
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