Energy Policy 46 (2012) 1–3

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Energy Policy

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Energy efficiency: Lessons from transport

Patrick Moriarty a,n, Damon Honnery b

a Department of Design, Monash University, Caulfield Campus, PO Box 197, Caulfield East, Victoria 3145, Australiab Department of Mechanical and Aerospace Engineering, Monash University, Clayton Campus, PO Box 31, Victoria 3800, Australia

a r t i c l e i n f o

Article history:

Received 29 March 2012

Accepted 25 April 2012Available online 8 May 2012

Keywords:

Energy efficiency

Transport energy efficiency

Transport outputs

15/$ - see front matter & 2012 Elsevier Ltd. A

x.doi.org/10.1016/j.enpol.2012.04.056

esponding author. Tel.: þ61 3 9903 2584; fax

ail address: patrick.moriarty@monash.edu (P.

a b s t r a c t

Many researchers have stressed the apparently great potential for improvements in energy efficiency to

dramatically decrease total energy use, but despite steady progress in the technical efficiency gains,

global primary energy use continues to rise. For transport, we show how the concept of energy

efficiency has been progressively expanded over time, as our ideas on what constitutes transport

output useful to individuals has evolved. Even the energy inputs regarded as necessary for transport

have undergone revision, because of the need to compare different modes. Finally we discuss the

relevance of the changes in our notions of transport efficiency for energy efficiency in general.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

According to noted energy researcher Amory Lovins (2004),energy efficiency can be defined as follows: ‘Broadly, any ratio offunction, service, or value provided to the energy converted toprovide it.’ Why improve energy efficiency? According to Cullenet al. (2011), the reasons include relieving energy resourcedepletion, saving energy costs, and reducing CO2 emissions. Manyresearchers have stressed the apparently great potential forimprovements in energy efficiency to dramatically decrease totalenergy use (see, e.g., Lovins, 2004; Socolow and Pacala, 2006,Barker et al., 2007, Cullen et al., 2011). Further, many energyefficiency improvements can be made at low or even negativemonetary cost. And as Wilhite (2008) has pointed out, the aim ofenergy policy appears now to rest on endeavours based onnarrow definitions of technical energy efficiency rather than thebroader concept of energy reduction, possibly because energyefficiency alone is seen as potentially making a major impact onenergy use and carbon emissions.

Despite steady progress in the efficiency of energy conversiondevices (power station turbines, car engines, jet engines, electriclighting, etc.), global primary energy use has continued to riseover time, in a roughly linear manner over the past half-century(BP, 2011). Energy-related CO2 emissions have grown in step withenergy use. Most of this rise is due to greatly increased numbersof energy-using devices, a result of continuing global economicgrowth. For example, the global car fleet has expanded fromabout 51 million in 1950 to over 800 million in 2007 (Moriartyand Honnery, 2011a). In a ‘business-as-usual world’ with

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: þ61 3 9903 1440.

Moriarty).

continued economic growth, official energy forecasts foreseecontinued global primary energy consumption (InternationalEnergy Agency (IEA) 2011; Energy Information Administration(EIA), 2011). It therefore seems unlikely that technical efficiencyimprovements to devices alone can do more than marginallyreduce energy use or greenhouse gas emissions, thus raising thequestion of the need for energy conservation.

Many researchers distinguish energy efficiency from energyconservation. Thus Oikonomou et al. (2009) write: ‘A cleardistinction between energy efficiency and energy conservationis that the former refers to adoption of a specific technology thatreduces overall energy consumption without changing the rele-vant behaviour, while the latter implies merely a change inconsumers’ behaviour’. This position is, however, in direct con-trast to that of Lovins who, by extending the concept outside thebounds set by purely technical definitions (based on, for example,the laws of thermodynamics), opened up the possibility of humanbehaviour being linked to energy efficiency.

Consider the case of electric power plant efficiency, whereinput and output are both energy terms. The net power outputfrom a given fossil fuel power plant, and so its energy efficiency,depends to some extent on the level of emissions control forparticulates, SOx and NOx. Today we increasingly accept that theseemissions must be stringently controlled, but such was notalways the case. The change came about because of changinglevels of tolerance for air pollution (Moriarty and Honnery,2011b). It might be argued that these emission controls had littleeffect on power plant efficiency, but what if CO2 emissionsbecome unacceptable? In that case the drop in overall powerplant efficiency from the installation of carbon capture technol-ogy would be very significant. Similar considerations apply tovehicular emissions and noise levels from road vehicles andaircraft. Along with speed limits, and compulsory vehicular safety

P. Moriarty, D. Honnery / Energy Policy 46 (2012) 1–32

equipment, these system-wide policies affect individual vehicleenergy efficiency.

In this paper we focus on transport energy efficiency. Inparticular, we look in Section 2 at how the concept of energyefficiency in transport has necessarily been broadened over timefrom simple transport equipment efficiency. In Section 3, wediscuss the relevance of these changes in our notions of transportefficiency for energy efficiency in general.

2. Evolution of the transport energy efficiency concept

Transport energy efficiency has been at the forefront in theexpanded notion of energy efficiency, partly because, historically,different modes with very different characteristics have competedto provide passenger and freight services. Here, passenger trans-port is used to explore the complexity of defining efficiency forenergy services. As a purely thermodynamic device, the efficiencyof the passenger car engine can be easily defined by its principlesof operation, and measured. However human interaction withpassenger vehicles gives rise to the concept of travel, so ratherthan output power, the distance travelled becomes the parameterto be maximised for a given fuel or energy input. Vehicleefficiency was thus initially simply thought of as distance tra-velled per unit of fuel consumed, or ‘miles per gallon’ (‘mpg’).Once defined, this human-derived measure of efficiency, or taskefficiency, enabled comparison of one car model with another.

With public transport vehicles, such a comparison is not verymeaningful, given their larger carrying capacity, although theycan be compared on a seat-km basis. But for well over a centurynow (see e.g. Swain (1898)), railways have had to define their taskin terms of passenger-km (and tonne-km for freight), simplybecause they charged fares and freight rates largely on this basis.Given that cars, buses and trains have long been consideredalternative modes of passenger transport, their actual or potentialefficiency could now be compared on a passenger-km/litre of fuelas well as a seat-km/litre basis. Such comparisons becameincreasingly common after the 1970s oil crises.

Even defining the transport task as passenger-km has itsdifficulties. For many decades now (see e.g. Ashton (1947)),transport researchers have considered that transport, whetherpassenger or freight, is (mainly) a derived demand, that the valueto us of passenger-km and tonne-km is that they satisfy somehuman need. But as Steg (2005) and Cao et al. (2009) havepointed out, much travel is not done to reach a destination butfor the pleasure that car travel (and to some extent, other forms oftravel) afford. Cao et al. also discuss other forms of travel for itsown sake, including: ‘‘‘unnecessary’’ trips to destinations, desti-nations that are farther away than ‘‘necessary,’’ and routes to agiven destination that are longer than ‘‘necessary’’’ (p. 254).Motorists, for example, often choose a route which will minimisetrip time, rather than trip length. In such cases it is problematicwhether the extra passenger-km generated by such trips shouldbe counted in the transport task. Presumably, some human needis satisfied, but it is not a transport need.

Similar considerations would apply to driver travel in ‘serve-passenger’ trips, which form an important share of total travel(Sharpe and Tranter, 2010). For the case of a parent driving onechild to school, then returning home, total passenger-km wouldneed to be reduced by two-thirds to more accurately reflect theattainment of desired access. In contrast, the travel of drivers ofpublic transport vehicles and taxis are not included in passenger-km statistics.

For public transport vehicles that use electric power ratherthan diesel fuel, a further refinement was necessary for mean-ingful comparison: transport modes must be compared on a

passenger-km/MJ of primary energy basis. If this was not done,the high conversion efficiency of electricity to mechanical energywould bias the results toward electric traction.

The comparison has already moved a long way from thesimple mpg comparisons, in several ways. First, the importanceof actual uptake of the potential energy service on offer isstressed; passenger-km is considered at least as important aspotential uptake (seat-km). Policy measures that could increasethe occupancy rate for both cars and public transport (such ashigh-occupancy vehicle lanes on arterial roads) are accordinglyconsidered to be transport energy efficiency measures. Withtypical occupancy rates of 1.5 persons per car, (or 30% seatoccupancy for a five-seat car), the potential for improvement isevident (Moriarty and Honnery, 2008a,b). If only seat-km per MJis stressed, the potential for seat occupancy increases is likely tobe overlooked.

Second, the entire transport fuel system supply chain is nowconsidered (‘well-to wheels’ efficiency), not just the ‘tank towheels’ efficiency implicit in mpg analyses. This is crucial,because as non-conventional fossil fuel sources such as Canadianoil sands are progressively tapped, the energy costs of extractionwill rise (Moriarty and Honnery, 2011b), partly offsetting anyfurther gains in vehicle engine efficiency. This will be furthercomplicated by the use of plug-in hybrid vehicles, which havetwo sources of fuel input. The availability and energy costs of thetransport fuel used thus become a further factor to consider inthis expanded notion of energy efficiency for transport. In future,it is even possible for tank-to-wheels efficiency gains to be madewhile the overall well-to-wheels efficiency is falling.

Third, alternatives to the dominant technology are considered,even though many would argue that private and public passengertravel—let alone non-motorised travel—cannot be readily com-pared. They could argue that on a door-to-door basis thesealternative modes are far slower than private car travel, andfurther, that private travel offers privacy, superior transportcapacity for luggage, ability to travel without reliance on time-tables, and so on. All these advantages are real, but supporters ofalternative modes can point to different advantages for thesemodes. Non-motorised modes—and the walking inevitably asso-ciated with accessing public transport—provide exercise for thetraveller. In this special case the energy expenditure may itself beregarded as a benefit rather than a cost, an output rather than aninput, and the overall energy efficiency of non-motorised travel isaccordingly even higher than usually calculated.

Public transport riders can and do read or even work whilethey travel. This use of travel time for other activities (includingphysical exercise) makes the notion of one mode being faster thananother, problematic (Lyons and Urry, 2005; Moriarty, 2002).Further, as Ivan Illich (1973) stressed several decades ago, thenotion of time spent on travel, and thus travel speed, should bemodified to include time spent working to pay for a car, forexample (and, presumably, also fares in the case of publictransport).

Although some authorities assume that non-motorised travelis only for those without other options, its popularity in the high-income Netherlands, where some 46% of all trips are non-motorised, argues against this assumption (Moriarty andHonnery, 2012). Shifting modes is now regarded as an importantmeans of improving overall transport energy efficiency, as well asachieving other aims.

Fourth, at least some behavioural change is assumed to beneeded, as in the case of mode shift. Also, driver behaviour itselfcan significantly influence energy efficiency, as is recognised inthe idea of ‘eco-driving’. According to a recent IEA report, fuelconsumption for a given level of travel can be reduced by perhapsas much as 20% for some drivers and an average of 5%–10% long-

P. Moriarty, D. Honnery / Energy Policy 46 (2012) 1–3 3

term reduction in fuel use for all drivers (including truck and busdrivers) can be achieved (Kojima and Ryan 2010). Measuresconsidered in eco-driving include minimising engine idling, anddriving at ‘energy efficient’ speeds (usually in the range 60–90 km/h). These recommendations, from a report entitled ‘Trans-port Energy Efficiency’ (Kojima and Ryan, 2010) show how fareven official organisations are prepared to extend the concept inthe direction of behavioural change.

3. Discussion: Extending the concept of energy efficiency

In this section we outline how energy efficiency analyses ingeneral might benefit from our discussion on transport efficiency.For the concept of energy efficiency to have meaning withinsystems designed to meet human needs, it must be defined as aratio of an output useful in some way to humans, to the inputenergy. This is not usually done in cases such as lighting orbuilding air-conditioning; lighting efficiency is commonly mea-sured as lumen per watt—whether anyone is getting benefit fromthe lighting, was, at least until recently, not considered relevant.

As with transport, we should consider alternatives to thedominant technology for meeting the relevant human need.Building temperature control can be achieved not only by air-conditioning but also by passive solar energy or geothermal heatpumps. The latter shows how difficult defining energy efficiencycan be: Are such heat pumps an alternative energy source(geothermal energy) or a means of improving the energy effi-ciency of conventional equipment? And how can we measure theefficiency of natural lighting, since lumen/watt is not relevant?

Energy efficiency is also not easily disentangled from beha-vioural change, as evidenced by the example of ‘eco-driving’.Kunz et al. (2009) discuss cases where designers of energy-efficient buildings greatly under-estimated actual energy use.Occupant behaviour, as well as equipment performance, provedcrucial for energy consumption. For example, the need for humanthermal comfort can to some extent be met by appropriateclothing—and even by acclimatisation (Auliciems, 2009).

What we learn from transport is that the definition of energyefficiency is dynamic and should evolve as circumstances change.Hence, rather than focussing on improving technical energyefficiency, policies intended to reduce energy use overall shouldgive far greater emphasis to how that energy is used to meethuman needs.

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