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Connecticut DOT Announces Hybrid Bus Testing Project Report

(Hartford, CT)—The Connecticut Department of Transportation (ConnDOT) announced today the results of a demonstration project involving two hybrid diesel-electric buses. ConnDOT’s goal in undertaking the project was to determine what type of vehicles to purchase in the future as bus fleets are replaced.

The study conducted by the Connecticut Academy of Science and Engineering in November 2005 was prepared for ConnDOT and CTTRANSIT, the operator of the state-owned bus system. The report concludes that both conventional state-of-the-art diesel buses and hybrid buses have advantages and limitations. The study recommends that ConnDOT continue to evaluate the current hybrid buses to understand their performance in extended service, and to continue to purchase small numbers of additional hybrid buses as newer designs become available.

Results of the 18-month testing showed that the hybrid buses demonstrated about 10% improved fuel economy compared to the base clean-diesel buses. The buses were popular among passengers and operators, who cited their quiet vibration-free ride. Despite the fact that these buses are of new design and are early in the product cycle, reliability performance of the hybrid buses met and exceeded expectations. Emissions for the hybrid buses and the comparison clean-diesel buses were found to be about the same; both were significantly cleaner than average emissions from older buses in the CTTRANSIT fleet.

The hybrid buses and comparison diesel buses underwent a three-phase in-depth test of fuel economy, reliability, maintenance expense and emissions. During the first phase of testing, the buses were run on the standard fuel for public transportation buses in Connecticut - #1 diesel fuel, a grade of diesel that is cleaner burning than what is available to the public at most fueling stations. In the second phase, the buses were switched to ultra-low-sulfur diesel fuel, a still cleaner fuel that will be required to be used in heavy-duty diesel engines by the end of 2006. Finally, the third and final testing phase was conducted with a diesel particulate filter added to the test vehicles.

During the testing period, the two buses operated on regular routes in the Hartford and Stamford areas. While most emissions testing is conducted in a laboratory, this program utilized innovative mobile on-board tailpipe emissions testing in an effort to make results more real world.

The demonstration and evaluation project was a collaboration of many organizations, including ConnDOT's Bureau of Public Transportation and Division of Research, the University of Connecticut, the Connecticut Academy of Science and Engineering, New Flyer Bus Company, Allison Electric Drive, Horiba Instruments, the East Coast Hybrid Consortium, and CTTRANSIT.

Results of the reports will be shared with the transit community with the hopes that, in conjunction with results of other testing projects, this study will assist both ConnDOT and the industry with future decision making. Follow-up studies are also recommended in the report, and the University of Connecticut has already submitted a proposal to do emissions testing on a “next generation” series hybrid in 2006.

Copies of the summary report are available from Stephen Warren, assistant general manager of maintenance services for CTTRANSIT, by calling 860-522-8101 ext 223 or e-mailing

CTTRANSIT is the state-owned bus transit system serving the greater Hartford, New Haven, Stamford, Waterbury, New Britain, Meriden, Bristol and Wallingford areas.

The Connecticut Academy of Science and Engineering is a non-profit institution patterned after the National Academy of Sciences to identify and study issues and technological advancements that are or should be of concern to the state of Connecticut. It was founded in 1976 by Special Act of the Connecticut General Assembly. The Connecticut Academy will provide expert guidance on science and technology to the people and to the state of Connecticut, and promote its application to human welfare and economic well being.