October 2012

Assessing the Costs for Hybrid versus Regular Transit

Authors INTRODUCTION Fuel costs are a significant portion of in 15 percent of the US transit fleet Shauna L. Hallmark transit agency budgets. Hybrid buses could reduce fuel consumption by Interim Director, Institute for Transportation; offer an attractive option and have the 50.7 million gallons of diesel annually. Professor, Civil, Construction, and However, purchase of hybrid transit Environmental Engineering potential to reduce operating costs for Iowa State University agencies significantly. buses requires a significant investment. 515-294-5249, [email protected] Hybrid technology has been available In addition, early estimates of cost Bo Wang and Yu Qiu in the transit market for some time. savings may not have materialized to Student Research Assistants As of 2009, there are more than 1,200 the extent transit agencies expected. Iowa State University hybrid buses in regular service in Other costs, such as the cost of North America in more than 40 transit replacing batteries and reduced Bob Sperry agencies (Transport Canada 2011). The maintenance, are also issues that Iowa Local Technical Assistance Program majority of these buses are regular 40 have not been substantiated with Iowa State University ft buses, although some smaller (20 ft) independent studies. To justify the shuttle buses and larger articulated (60 expenditure, agencies require more Sponsor ft) buses are also in service. quantitative information about the likely fuel economy, maintenance, and Iowa Energy Center The transit agency in New York, New other costs for hybrid buses. For More Information York has approximately 1,000 hybrid www.intrans.iastate.edu/ vehicles as of 2009 (Maynard 2009) and Toronto, Canada has approximately 33 OBJECTIVES percent (Transport Canada 2011). This technical brief summarizes The main reasons agencies consider information about the costs and benefits hybrid transit vehicles are fuel savings that have been attributed to use of and reduced emissions. Hybrid electric hybrid transit buses as found in the buses offer an attractive option and literature. Results from a demonstration have the potential to reduce operating project that compared fuel economy costs for transit agencies significantly. and emissions for 12 hybrid buses and 7 Wayne et al. (2009) estimated that control buses for the transit agency for use of diesel-electric hybrid buses Ames, Iowa and Iowa State University, CyRide, were also included.

One of 12 hybrid CyRide buses Assessing the Costs for Hybrid versus Regular Transit Buses

offset by participation in programs that fuel economy was 48 percent Costs and benefits include initial such as the American Recovery and higher for the hybrid buses. purchase cost differentials, savings Reinvestment Act (ARRA) or Clean A study by Battelle (2002) tested in fuel, reduced emissions, potential Fuels grant programs (EESI 2012). emissions using a dynamometer for reduced maintenance due to decreased Funding packages to offset the one diesel hybrid-electric and two engine and brake wear, and replacement purchase cost often make it much regular diesel buses (with and without costs for the hybrid battery pack. All easier for transit agencies to invest in catalyzed diesel particulate filters/ costs are listed in US dollars (USD). the technology that can reduce the DPFs). The researchers reported that lifecycle costs of hybrid buses. As an fuel economy for the hybrid bus was example, the CyRide agency in Ames COSTS 54 percent higher than the two regular purchased 12 hybrid buses through a diesel buses. The following sections discuss common Transit Investments for Greenhouse Gas costs that transit agencies consider and Energy Reduction (TIGGER) grant In another study, two buses were tested in long-term cost analyses for hybrid sponsored by the U.S. Department of using a dynamometer at the National buses. Information was summarized Transportation. Renewable Energy Laboratory (NREL) from a survey of existing literature, web ReFUEL facility in Golden, Colorado resources, and the team’s experience Fuel Economy (Chandler and Walkowicz 2006). with evaluation of hybrid school buses Actual savings depend on usage and One bus was a conventional diesel and hybrid transit buses (Hallmark et and the other was a hybrid bus and al. 2010 and Hallmark et al. 2012). The fuel costs, but improved fuel economy is the main savings associated with use both were tested over several drive term “cost” is used in the generic sense cycles including Manhattan, Orange of being a positive cost or negative of hybrid transit buses. Early estimates of fuel savings for hybrid buses over County Transit A (OCTA), CBD, and cost (benefit). As a result, costs may be (KCM) Transit in actual costs or reductions in costs. conventional buses were based on laboratory studies that demonstrated , Washington. Results indicate 30.3 percent lower fuel use for the KCM Purchase Cost significant fuel savings. cycle, 48.3 percent lower for the CBD The difference in initial purchase Chassis dynamometer tests were cycle, 50.6 percent for the OCTA cycle, price between a hybrid and conducted for 10 low-floor hybrid and 74.6 percent for the Manhattan regular transit bus can be substantial. buses and 14 conventional high-floor cycle. Fuel economy was reported as Based on 2011 values in the US, the diesel transit buses run by New York miles per gallon. purchase cost of a regular 40 ft bus is City Transit (NYCT) (Chandler and $280,000 to $300,000 compared to a Walkowicz 2006). Buses were evaluated In another study, Clark et al. (1987) hybrid bus that is between $450,000 over three driving cycles including evaluated six transit buses with and $550,000. Because of the difference, the Central Business District (CBD), traditional diesel engines, two powered agencies are anxious to recoup the cost the New York (NY) bus cycle, and by spark-ignited compressed natural gas differential through savings in fuel and the Manhattan cycle. The operating (CNG), and one hybrid transit bus in maintenance. costs, efficiency, emissions, and overall City using a mobile heavy-duty performance were also compared while emissions testing lab. Buses were tested In some cases in the US, the purchase both types of buses were operating on over a driving cycle representative of price of hybrid transit buses has been similar routes. The researchers found transit bus operation, which was developed using global positioning system (GPS) data from in-use transit buses. Depending on how fuel economy was evaluated, the hybrid bus ranked fourth and first in fuel economy. Transport Canada (2011) evaluated hybrid transit buses for several transit agencies in Canada. In one laboratory study using the Manhattan Test Cycle, the authors found a reduction in fuel consumption of 36 percent. In a test track study, the authors found a 28 percent fuel reduction for hybrid transit buses compared to regular buses when the buses were operated at an average CyRide engine and electric motor setup (left) and battery pack configuration (right) speed of 10 km/h with 10 stops per

2 Hallmark, Wang, Qiu, and Sperry kilometer. As average speed increased, economy were laboratory tests that months of hybrid transit bus operation the differences in fuel consumption do not always replicate actual on-road in , no significant additional were smaller. conditions. maintenance issues occurred with hybrid buses. In a later test track study, the authors Fuel economy varies and is correlated found average fuel use reduction to to a number of factors including Although early maintenance problems be 28 percent. The researchers also number of stops per unit distance, road have been present, most of the initial reported that the Toronto Transit grade, surrounding traffic volume and maintenance is covered by manufacturer Corporation, which has about 500 conditions, environmental conditions, warranties and is not likely to hybrid buses, was only achieving a driving style, type of hybrid technology have additional costs to the transit reduction of 10 percent for in-use fuel (parallel versus series) (Liang et al. companies. consumption. 2009), roadway type, and passenger One study was available that load (Frey et al. 2007). Given driving A study was conducted by the Center summarized operating costs other than style can have a significant impact on for Transportation Research and fuel economy. KCM evaluated operating the fuel economy of hybrid buses, many Education (CTRE) at Iowa State costs using a cost of $1.98 per gallon transit agencies provide training for University (ISU) to study the fuel for diesel for 60 ft buses. For regular their drivers. economy of 12 hybrid transit buses. transit buses, they found that fuel costs Seven control buses with similar Short-Term Maintenance and were 79 cents per mile and maintenance characteristics were also evaluated. Operating Costs costs were 46 cents per mile, for a total operating cost of $1.25 per mile. Average fuel economy for hybrid buses Short-term maintenance costs have not In comparison, diesel-electric hybrid was 11.8 percent higher than for control been well quantified. Some agencies buses had fuel costs of 62 cents per buses (Hallmark et al. 2012). The study have experienced up-front maintenance mile with maintenance costs of 44 cents also showed that fuel economy was issues with hybrid buses. NYCT per mile for a total cost of $1.06 per correlated to number of passengers per reported initial issues with batteries mile (Chandler and Walkowicz 2006). route, average running speed, average and need for software modifications Hence, the savings were 19 cents per acceleration, average deceleration, (Chandler and Walkowicz 2006). The mile. percent of time spent in acceleration, Ames transit system, which purchased and season. 12 hybrid transit buses in 2010, has Long-Term Maintenance Costs reported the need for various software Fuel economy estimates from various Several long-term costs/benefits adjustments to achieve better fuel studies are summarized in Table 1. To contribute to the lifecycle equation economy, given initial fuel economy was make the table consistent, differences in for a hybrid bus versus a conventional much lower than expected. In addition, fuel economy were normalized to show bus. However, hybrid buses have not adjustments to the brake pedal had to decrease in fuel consumption (rather been on the market long enough for be made (Hallmark et al. 2012). than improvement in fuel economy) these costs/benefits to be substantiated given this information was presented Transport Canada (2011) also reported by transportation agencies. Potential both ways in the various studies. issues early on but indicated later that long-term costs/benefits include As noted, fuel economy savings range mean distance between failures was those associated with reduced engine from 10 to 74.6 percent. However, most similar to that of regular transit buses. wear, replacing the battery pack, and of the studies showing significant fuel Transport Canada found that after eight increased bus weight. Initial feasibility studies and marketing Table 1. Summary of fuel economy performance of hybrid versus conventional transit buses of hybrid school buses indicated that the hybrid technology would result Reduction in Fuel in less engine wear and regenerative Consumption for Hybrid Study braking was estimated to result in less Agency Sample Size versus Regular Buses (%) Type brake wear (IC Bus 2011, Thomas Built Transit 10 hybrid and 14 conventional 32 Laboratory 2011, and Pritchard et al. 2011). (Chandler et al. 2002) diesel transit buses Transport Canada (2011) reported a 50 Battelle (2002) 1 hybrid and 1 regular 35 Laboratory to 100 percent improvement in brake NREL (Chandler and 1 hybrid and 1 regular over 30 to 75 Laboratory Walkowicz 2006) several drive cycles life for hybrid transit buses. Transport Canada (2011) 8 hybrid and 6 regular 36 Laboratory However, replacement battery costs are buses 28 Test track expected to add to the lifecycle cost of hybrid buses. IC Bus (2011) indicates 500 10 In-use that lithium-ion batteries have a life of CyRide (Hallmark et al. 27 12 In-use five to seven years, but the replacement 2012)

3 Assessing the Costs for Hybrid versus Regular Transit Buses costs are still somewhat unknown. and 40 percent for CO2. HC emissions, mile. As indicated, emissions were lower Battery technology/economics are however, increased by 88 percent for the in all cases for the hybrid bus, except evolving rapidly, so costs will depend on hybrid buses. for the CO2 emissions on the CBD and this when it’s time to replace the battery the cases where the differences were not With the Manhattan cycle, the pack. statistically significant (indicated as NS researchers found a decrease for the in the table). Finally, Iowa school districts that hybrid buses of 98 percent for CO, 44 piloted hybrid electric school buses percent for NOx, 28 percent for HC, 99 Clark et al. (2006) evaluated six transit were concerned that the weight of the percent for PM, and 33 percent for CO2. buses with traditional diesel engines battery pack may increase wear on some including two powered by spark-ignited In another study, emission tests for one parts, such as shock absorbers and tires compressed natural gas (CNG) and diesel hybrid- and two diesel (Hallmark 2010), given the battery one hybrid transit bus. This evaluation buses (the Orion V with and without pack for hybrid school buses added was conducted in Mexico City using catalyzed DPFs) were evaluated using approximately 2,000 lbs to each bus. a transportable, heavy-duty emissions a dynamometer in , Canada Data on this concern are not available at testing lab and buses were tested over a (Battelle 2002). The buses were tested this time. driving cycle representative of Mexico on the CBD cycle using ultra-low sulfur City transit bus operation, which was diesel (ULSD) #1 fuel. Reduced Emissions developed using GPS data from transit Reduced emissions are one of the main The researchers indicated that the buses in use. hybrid bus had 94 percent lower benefits attributed to hybrid buses. Depending on how emissions were emissions for CO, 49 percent lower A number of studies have indicated compared, the hybrid bus and one of for NO , 120 percent higher or HC, 93 a substantial reduction in pollutants x the CNG buses had the lowest NO percent lower for PM, and 37 percent x for hybrid buses over regular transit emissions of the nine buses tested. lower for CO than the diesel bus buses. Wayne et al. (2009) conducted 2 Particulate emissions from the hybrid without a catalyzed DPF. an evaluation scenario comparing use bus were less than 10 percent of the of hybrid transit buses to regular transit Emissions for the hybrid bus compared average PM emissions for the diesel- buses. The authors estimated that use to the diesel bus with the catalyzed DPF powered buses. The hybrid bus and of diesel-electric hybrid buses in just installed were 38 percent lower for CO, one of the CNG buses had the lowest 15 percent of the US transit fleet could 49 percent lower for NOx, 450 percent CO emissions, and the hybrid bus and reduce annual emissions by 1,800 tons higher for HC, 60 percent lower for PM, buses equipped with a continuously of carbon monoxide (CO), 400 tons and 38 percent lower for CO2. These regenerating trap (CRT) exhaust after- of hydrocarbons (HC), 4,400 tons of tests were conducted in February 2000. treatment had hydrocarbon emissions nitrogen oxides (NO ), 200 tons of x that were below the detectable limit of In another study, two buses—one from particulate matter (PM), and 491,400 the instrument used. a conventional diesel fleet and another tons of carbon dioxide (CO2). from a hybrid fleet—were tested using Shorter et al. (2005) used a chase- Chandler et al. (2002) conducted a dynamometer at the NREL ReFUEL vehicle sampling strategy to measure chassis dynamometer tests for 10 low- facility in Golden, Colorado (Chandler NOx from 170 in-use New York City floor hybrid buses and 14 conventional and Walkowicz 2006). The buses transit buses. The authors sampled high-floor diesel transit buses run by were tested over several drive cycles emissions from conventional diesel NYCT. The buses were tested over including Manhattan, OCTA, CBD, buses, diesel buses with continuously three driving cycles: the CBD, NY, and KCM. These tests were conducted regenerating technology, diesel hybrid- and Manhattan. The operating costs, in May and June 2005 and results are electric buses, and CNG buses. The efficiency, emissions, and overall shown in Table 2 for each drive cycle. authors found that NOx emissions from performance were also compared while CNG buses and hybrid buses were Table 2 shows the percentage difference both types of buses were operating on comparable. NO emissions for the in emissions among the buses. x similar routes. Data were collected from hybrid buses were approximately half of Emissions were reported in grams per 1999 through 2001. those for conventional transit buses. Results indicated that, for the CBD cycle, emissions for the hybrid transit Table 2. Summary of NREL percentage decreases for hybrid versus regular buses buses were 97 percent lower for CO, 36 Cycle CO NOx HC PM CO2 percent lower for NOx, 43 percent lower for HC, 50 percent lower for PM, and 19 Manhattan NS -38.7 NS -92.6 -43.8 percent lower for CO2. OCTA -32.0 -28.6 NS -50.8 -34.5 Results from the NY bus cycle showed CBD -48.0 -26.6 -75.2 -97.1 34.8 a decrease of 56 percent for CO, 44 KCM -59.5 -17.8 -56.3 NS -24.1 percent for NOx, 77 percent for PM, NS = Not statistically significant (Chandler and Walkowicz 2006)

4 Hallmark, Wang, Qiu, and Sperry

In contrast, Jackson and Holmen (2009) collected second-by-second particle number (PN) emissions from four conventional and one hybrid transit bus in Connecticut over six pre-defined test routes that had multiple road types and ranges of driving conditions. For most of the routes, the authors noted few differences between the conventional and hybrid transit buses. However, the hybrid had higher emission rates on two routes with steep uphill grades and PN emissions were 51 percent higher on one route and 24 percent higher on the other. Close up of CyRide engine (left) and engine compartment (right) Hallmark et al. (2012) evaluated three hybrid and two control transit buses for ranges. Differences ranged from 0.8 to Other Benefits and Costs the City of Ames CyRide transit system. 3.5 mg/s (18.4 to 40.1 percent) higher. Emissions were tested using a portable Although also difficult to quantify, emissions monitoring system (PEMS). Although significant reductions in another benefit of hybrid buses is Speed, acceleration, and passenger load emissions have been reported, it is reduced noise due to either a smaller were also collected and emissions were difficult to allocate costs to pollutant internal combustion engine or correlated to vehicle-specific power reduction. Factors in the selection of lower revolutions per minute (RPM) (VSP), which has been used as a proxy hybrid technology include political, (Transport Canada 2011). Use of variable for power demand or engine social, and environmental pressures to hybrid transit buses may also be a good load. reduce emissions, improve health, and marketing and public relations strategy, conserve energy. However, social costs given the buses promote environmental The researchers noted only minor associated with reduction in emissions sustainability. differences between buses for any and improved health are difficult to pollutant in the lower VSP ranges. In quantify, making it difficult to include SUMMARY the middle VSP bin ranges, emissions emission reduction in long-term cost were higher for control buses, with analyses. Although hybrid transit buses offer differences between 0.3 and 0.4 g/s (9.4 significant fuel savings and other to 27.3 percent higher). In the highest Agencies in non-attainment areas for benefits, there is still some concern that VSP ranges, emissions were significantly criteria pollutants have some methods it is difficult to recuperate initial capital higher for control buses than for hybrid to quantify costs. (The Clean Air Act costs (Transport Canada 2011). Hybrid buses with differences between 0.7 and and Amendments of 1990 define a buses have not yet been in service 2.7 g/s higher (15.0 to 97.0 percent). nonattainment area as a locality where through the 15 to 20 year service life air pollution levels persistently exceed that is used by transit agencies. Average carbon monoxide emissions National Ambient Air Quality Standards were higher for control buses than or that contributes to ambient air This technical brief summarized costs hybrid buses. In the medium- and quality in a nearby area that fails to for hybrid transit buses compared higher-VSP bins, control buses had CO meet standards.) A report by the Transit to conventional transit buses based emissions that were higher than hybrid Cooperative Research Program (TCRP on a summary of the literature, web buses by 1.0 to 3.1 mg/s (1.35 to 3.07 2000), for example, estimated a value resources, and team experience. Costs times higher). of $1,000 per ton of NO reduced and include those related to initial purchase x cost differentials, savings in fuel use, Control buses had HC emissions that $3,000 per ton for volatile organic reduced emissions, potential reduced were 1.2 to 1.8 mg/s higher in the compounds (VOCs). maintenance due to decreased engine mid-VSP ranges (68.5 to 131.0 percent Obviously, one additional problem for and brake wear, and replacement of higher). In the higher VSP ranges, use of cost-reduction benefits involving the hybrid battery pack. To quantify emissions were much higher for control pollutants is that cost savings are not lifecycle costs fully, agencies will need buses than hybrid buses by 2.3 to 3.0 usually accrued to the transit agency, additional information about actual mg/s (94.2 to 182.8 percent). making it more difficult to assess long- costs as well as methods to calculate Average nitrogen oxide emissions were term agency costs. savings from non-tangibles such as higher for the hybrid than the control reduction in emissions. buses in the mid to higher VSP bin

5 Assessing the Costs for Hybrid versus Regular Transit Buses

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