Transit buses made of plastic are about to turn from fanciful concept into road reality.
The country's fifth-largest bus manufacturer and one of the largest U.S. metropolitan transit authorities are vying to put plastic buses on the streets as early as the next 18 months.
Working separately, they want to replace the body of a city bus, made with rugged steel, with one made from composite materials using fiberglass. The lighter-weight material, saving as much as 5,000 pounds per bus, could lower both emissions and fuel costs dramatically.
It is an idea that could have been attempted years ago, said Arthur Crabtree, engineering manager for the Los Angeles County Metropolitan Transportation Authority in California.
``We were frustrated with what we saw from bus manufacturers,'' Crabtree said. ``They were using 1940s technology in the 1990s and not coming up with anything really new or inventive. There was no sense in mass transit falling behind in technology when there is a big demand for buses.''
Instead of working with a bus manufacturer, the transportation authority joined forces with military aircraft maker Northrop Grumman Corp. of Los Angeles. In 1992, the unlikely partners launched a $51 million development program, with 80 percent of the funding coming from the Federal Transit Administration. The rest of the funding came from the county authority.
Northrop Grumman has no desire to enter the bus business, said spokesman James Hart. But the proposal seemed an ideal way to put aircraft technology to good use for ground transportation.
The defense contractor had used composite bodies, with a fiberglass-composite mix attached to a urethane-foam core, on many of its military planes, Hart said.
Hence, the loose name of the concept, derived from B-2 bombers: the Stealth Bus.
``Weight [savings] opens up all kinds of advantages for buses,'' Hart said. ``The single-biggest expense for bus programs is maintenance. Making them lighter cuts down on wear and tear from braking and other operating costs.''
The vehicle, officially known as the Advanced Technology Transit Bus, or ATTB, borrows another aircraft approach: The team crafted a powertrain that runs with a hybrid of compressed natural gas and an electric propulsion system. The hybrid powertrain reduces emissions as much as 80 percent from traditional buses, Hart said, and cuts the bus's weight another 5,000 pounds.
The team used adhesive bonding to attach the bus body instead of traditional metal fasteners, further cutting weight and parts inventory. The roof, bus sides, floor and two ladders were laid horizontally and then bonded in one piece, Hart said.
A review board of transit providers from 20 U.S. cities and the Federal Transit Administration approved the conceptual design plans before six 43-passenger bus prototypes were built. The work is to be completed by year's end.
The Los Angeles-based transit authority eventually wants to convert its entire fleet of 2,300 buses to buses made with plastic skins and hybrid engines. The authority plans to put out a bid request by the end of September to build the first 500 buses using that concept, Crabtree said. The bid will be awarded by the beginning of 1999, he said.
The authority would like those buses on the road within 18 months, he said. But Crabtree admits that is a tall order. First, a company willing to act as contractor for the buses must be found. Crabtree did not expect that source to be a conventional bus manufacturer, due to the project's unique approach.
``This opens new opportunities for someone,'' he said.
Next, the bus must go through a punishing series of tests, including finite element analyses to detect whether composite joints and connections can withstand potholes and other road stresses. The bus will undergo a road simulator to see if it can endure 12 years of travel or 500,000 miles of structural pounding.
Fiberglass is the authority's first choice of skin material, due to its low cost and proven aerospace applications. But Crabtree said he would not rule out others until after testing. The 40-foot bus needs to weigh about 21,000 pounds, or about 10,000 pounds less than a steel bus.
Finally, the authority would like each bus to cost about $325,000 to build — or close to the cost of building a metal bus, Crabtree said.
Yet-another player in the California bus market plans to join the composite conversion. Manufacturer North American Bus Industries Inc. of Moorpark, Calif., wants to build a prototype plastic bus body by early next year. The firm would like to make a plastic-shelled bus in the year 2000.
That company, known as NABI, was inspired partly by the work done by Northrop Grumman, said Bill Coryell, vice president of sales. But the firm is moving a bit more cautiously by not including the hybrid electric-powered propulsion system on the drawing board in Los Angeles County.
``I don't think a composite bus is that hard to achieve,'' Coryell said. ``The ATTB project was a considerable step forward in the state of the art. We'd be happy to spend the money for it if the capital costs are justified by lower operating costs.''
NABI is advancing plastics processing in its pursuit of composite bus technology. The bus maker has licensed technology from molder and toolmaker TPI Composites Inc. of Warren, R.I., to build an entire plastic bus skin.
That body would be made from a mix of about 70 percent fiberglass combined with polyester for strength, Coryell said.
TPI would make the body panels through a Scrimp process that involves laying up the fiberglass laminate on the open mold, applying a gel coat, placing a vacuum bag on it and then infusing the polyester resin.
TPI plans to build both a 30-foot bus shell — which can be used by car rental agencies and other companies for city transit — and a 40-or 45-foot bus for routine city driving, said TPI President Everett Pearson.
TPI is completing the tooling for the Scrimp process this year at its 250,000-square-foot plant, he said. The molder has made composite bodies for sailboats and electric cars.
``In the Scrimp system, you can make lightweight and strong parts,'' Pearson said. ``Because the vacuum pulls in the resin, you get no heat. The idea has a lot of merit, and it's something we can do well here.''
Like the Los Angeles County buses, NABI's prototypes will be put through rigorous impact testing. The prototypes, expected on the road by mid-1999, will undergo crash tests from a 4,000-pound car, rollover tests and sundry fuel, handling, stability and durability testing, Coryell said.
NABI expects to produce small volumes at first, depending on demand, he added. Each bus will weigh about 5,000 pounds less than its steel counterpart.
Whatever ends up on the road will be an improvement over the lumbering metal bus hulks now gulping fuel at alarming rates, Crabtree said.
``I was skeptical at first but now I'm a believer,'' he said. ``It's been one heck of an education.''