Technologies: Lightweight Materials
Anything that lowers the weight of a transit vehicle will improve its fuel efficiency. The lighter the weight of a vehicle, the less fuel (of whatever type) will be required to propel it. Currently, several manufacturers have brought to market an alternative to the conventional, steel/aluminum-frame bus: the composite fiber bus body. Made either of expensive but very strong carbon fiber, or more affordable but still sufficiently strong fiberglass, composite fiber bodies can offer decreased weight together with other features that would reduce operating and maintenance costs for a transit agency.
Based on a program run in the early 1990's, Houston's Metro determined that, as Metro Senior Director of Bus Maintenance John Franks put it, "Lightweight buses pay for themselves." Houston's German-made, carbon fiber bus required a smaller diesel engine, which led to immediate savings; Houston also expected future savings from reduced brake and tire wear and better mileage.
Between 1992 and 1999, Los Angeles MTA operated 6 much less expensive, fiberglass, single frame buses with favorable results. Composite fiber buses impressed the MTA with their resistance to corrosion, and their strength in collisions. Composites are "incredibly strong for their weight," remarks MTA's John Drayton.
MTA also took note of the precision engineering behind the composite manufacturing process. While a typical steel bus has 10,000 parts holding it together, current lightweight models have less than 50. The effect of fewer parts on the performance of the vehicle is, as Drayton put it, that "everything works better." "We are very confident about the potential for composite materials in transit buses." The production techniques involved in casting a single shell, or monocoque frame, Drayton emphasizes, "aren't rocket science, but techniques used in the boating industry for years," where they are used to create materials that withstand stresses of similar magnitudes.
While composite materials currently in demonstration have yet to prove themselves over the 12-year life span of a typical transit bus, so far there are few indications that testing will diminish the transit industry's high expectations for composites.
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