Journal of Transportation Technologies, 2013, 3, 52-57 http://dx.doi.org/10.4236/jtts.2013.31006 Published Online January 2013 (http://www.scirp.org/journal/jtts) Evaluation of In-Use Fuel Economy for Hybrid and Regular Transit Buses Shauna L. Hallmark, Bo Wang, Yu Qiu, Robert Sperry Iowa State University, Ames, USA Email: shallmar@iastate.edu Received October 9, 2012; revised November 10, 2012; accepted November 24, 2012 ABSTRACT Fuel costs are a significant portion of transit agency budgets. Hybrid technology offers an attractive option and has the potential to significantly reduce operating costs for agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Laboratory tests have indicated that hybrid transit buses can have significantly higher fuel economy and lower emissions compared to conventional transit buses. However, the number of studies is limited and laboratory tests may not represent actual driving conditions since in-use vehicle operation differs from laboratory test cycles. Several initial studies have suggested that the fuel economy savings reported in laboratory tests may not be realized on-road. The objective of the project described in this paper was to evaluate the in-use fuel econ- omy differences between hybrid-electric and conventional transit buses for the Ames, Iowa (USA) transit authority. On-road fuel economy was evaluated over a 12-month period for 12 hybrid and 7 control transit buses. Fuel economy comparisons were also provided for several older in-use bus types. Buses other than the control and hybrid buses were grouped by model year corresponding to US diesel emission standards. Average fuel economy in miles per gallon was calculated for each bus group overall and by season. Hybrid buses had the highest fuel economy for all time periods for all bus types. Hybrid buses had a fuel economy that was 11.8% higher than control buses overall and was 12.2% higher than buses with model years 2007 and higher, 23.4% higher than model years 2004 to 2006, 10.2% higher than model years 1998 to 2003, 38.1% higher than for model years 1994 to 1997, 36.8% higher for model years 1991 to 1993, and 36.8% higher for model years pre-1991. Differences between groups of buses also varied by season of the year. Keywords: Hybrid Vehicle; Fuel Economy; Transit 1. Introduction Fuel costs are a significant portion of transit agency budgets. Hybrid buses offer an attractive option and have the potential to significantly reduce operating costs for agencies. Hybrid technology has been available in the transit market for some time. There are over 1200 hybrid buses in regular service in North America in over 40 transit agencies as of 2009 [1]. The majority are regular 40-foot buses although some smaller (20-foot) shuttle buses and larger articulated (60-foot) buses are also in service. Hybrid technology offers an attractive option and has the potential to significantly reduce operating costs for agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Wayne et al [2] estimated that use of diesel-electric hybrid buses in 15% of the US transit fleet could reduce fuel consump- tion by 50.7 million gallons of diesel annually. However, purchase of hybrid transit buses requires a significant investment for transit agencies since a hybrid bus costs approximately 50% to 70% more than a con- ventional diesel transit bus [3]. Additionally, early esti- mates of fuel savings were based on laboratory studies which demonstrated significant fuel savings and actual in-use savings may not have may not have materialized to the extent transit agencies expected. 2. Background Laboratory tests in general have indicated that the fuel economy of hybrid transit buses is significantly better than for regular buses. Chassis dynamometer tests were conducted for 10 low-floor hybrid buses and 14 conven- tional high-floor diesel transit buses run by New York City Transit [4]. Buses were evaluated over three driving cycles including the Central Business District (CBD), New York bus cycle, and the Manhattan cycle. The oper- ating costs, efficiency, emissions, and overall perform- ance were also compared while both types of buses were operating on similar routes. They found that fuel econ- omy was 48% higher for the hybrid buses. A study by Battelle [5] tested emissions using a dyna- mometer for one diesel hybrid-electric bus and two regular Copyright © 2013 SciRes. JTTs