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| FOCUS ON TECHNOLOGY |
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| New Heavy-Duty Buses Improve Ride, Save Fuel |
| BY JAMES P. BURKE Chief, Public Transit Division City and County of Honolulu Department of Transportation Honolulu, HI |
The City and County of Honolulu Department of Transportation Services, along with Oahu Transit Services, Inc., find themselves in a position to take advantage of the many benefits offered by today’s ongoing vehicle technology advancements. Escalating energy and maintenance costs and the call for greener business practices have prompted bus and component manufacturers to provide products that offer greater passenger comfort, improved fuel efficiency, and decreased exhaust emissions. The use of lighter materials in manufacturing, hybrid propulsion packaging, and the reduction of engine parasitic loads are all strategies being employed by the industry as a whole. Honolulu is excited to be in a position to take advantage of today’s heavy-duty transit bus technology advancements. It’s looking forward to lower life cycle costs and improved vehicle performance. Some of the many new technology-enhanced sub-systems being evaluated by Honolulu today are Engineered Machined Products, Inc.’s (EMP) electrified engine cooling, electrified air conditioning, LED lighting, and hybrid drive propulsion.
Over the last two years, the City and County of Honolulu have taken delivery of 54 new heavy-duty transit vehicles equipped with fully-electrified air conditioning systems. The all electric air conditioning systems have greatly improved passenger ride comfort by reducing ambient interior noise, in some applications by as much as 8 dBA. They have also achieved a two percent average fuel savings by replacing the power consuming 6-cylinder refrigerant compressor with an auxiliary generator requiring one-third the driven horse power requirement. Honolulu is convinced electrified air conditioning will become the standard for future bus procurements.
A very impressive development in engine cooling technology is the all new EMP Mini Hybrid Thermal Management system. Honolulu ran a two and a half year study on two buses retrofitted with the new EMP system. Both units performed exceptionally well throughout the entire evaluation period with a minimum amount of maintenance. Benefits include better fuel economy, lower maintenance costs, improved safety by the elimination of hydraulic leaks, and improved emissions. Their in-house chassis dynamometer test confirmed an amazing 21-horsepower increase at the rear wheels over the original hydraulically driven cooling system. So impressive were the results of the study that 90 additional Mini Hybrid EMP retrofit kits were ordered and are scheduled for installation. Fifteen percent of Honolulu’s heavy duty transit vehicle fleet is equipped with a parallel hybrid propulsion system. Vintage models run from 2004 to 2010. An increase in fuel mileage and improved vehicle performance are two major benefits of hybrid packaging. Fuel mileage increase has been noted in the high 30 percentile range over similar vehicles configured with straight diesel power and operating in a mix of CBD and arterial duty cycles. Pull away from the curb acceleration is unmatched by any other sub-fleet and exterior noise has been significantly reduced.
 Honolulu was recently awarded an FTA Transit Investment for Greenhouse Gas and Energy Reduction grant to test and evaluate eight battery-dominant turbine-powered buses. It is anticipated that a battery-dominant system, whether powered by a small engine or a turbine auxiliary power unit , will yield a lower life cycle cost. The battery-dominant design fully decouples the traction motor from the power plant. It also eliminates the transmission, a significant maintenance item on a transit bus. Major series-hybrid components such as the energy storage system and drive unit are less costly to replace as well. Another benefit is the system’s reduced overall weight. And, if the power plant is a turbine it is inherently fuel flexible and could utilize several fuel alternatives including diesel, bio-fuels, or kerosene.
Honolulu looks forward to running an “apples to apples” comparison of turbine hybrid buses versus parallel-hybrid buses powered with conventional heavy-duty diesel engines operating in the same dense urban resort environment. The battery-dominant design will continue the electrification of bus components including air compressors and power-steering.
Technology advancement in the field of transportation is fast evolving. As Honolulu moves forward in the 21st century, technology has become the engine that drives much of its equipment decision-making. Honolulu’s transit future depends on sustainability; technology will help get us there!
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