How practical is the concept of alternative fuels, especially for trucks? We don't know until they're tested on actual pavement. The best way is to run them in actual service, and United Parcel Service (UPS), the giant express carrier, has hundreds of alternative-fueled delivery trucks from semis to minivans in operation.

UPS showed off several at the recent Michelin Challenge Bibendum in southern California. The Bibendum (named after the “Michelin Man”) is a festival of sometimes whimsical, occasionally usable and always interesting vehicles. Two previous events were held in France, the national home of Michelin Tire, the sponsor.

The 2001 Bibendum included a display of cars and trucks at the California Speedway in Fontana. Many entries competed for handling, quietness and fuel economy titles, and then caravaned up Interstate 15 some 275 miles to Las Vegas.

Not in the caravan but available for touching and feeling was a trio of UPS trucks that you may see if you're in the L.A. Basin: a Mack CH600 tractor and a “package car” walk-in van, both of which burn natural gas, and an electric-powered Dodge Caravan.

All run every working day and haul real packages delivered by real drivers. UPS let visitors drive the “electrovan” and the package car, but not the Mack.

The Mack's 12-liter, 350-hp diesel runs on liquefied natural gas, or LNG. The engine is an E7 fitted with special plumbing, ignition system and spark plugs to fire the gas. A pair of 150-gallon insulated tanks carry the liquid gas, pressurized at 250 pounds per square inch and super-cooled to minus 250 degrees Fahrenheit.

The single-rear-axle tractor runs every working day out of the UPS terminal in Ontario, Calif. It pulls a pair of 28-foot trailers about 140 miles to Desert Center, where it swaps the trailers for two brought from Phoenix by a standard tractor, then returns to Ontario. Normal combined gross weights are 65,000 to 80,000 pounds.

“The driver likes it,” said Jim Breeher, an automotive manager at UPS' Ontario shop. "It runs smooth and quiet." There's also no smoke, even when starting cold, and no fumes, because only odorless LNG is burned.

UPS has 12 other LNG tractors like this and will buy more, according to Mike Herr, corporate environmental affairs manager at UPS. Tax breaks and other special incentives from federal and some state governments offset their high purchase cost –- about $50,000 extra per tractor, he said.

Another expense is the cryogenic fueling station, which costs $250,000 to $500,000. UPS has one in Ontario and others elsewhere, and trucks that have to be fueled from them cannot roam far. This is not a problem for UPS because its power units all run out of assigned terminals and return home each day or night.

This Mack averages only a bit over 3 miles per gallon, Breeher said. But here LNG costs 65 cents to $1 a gallon, vs. $1.40 to $1.60 or more for diesel. So the cost per mile is about the same or less than for a standard diesel engine, and the cleaner-burning LNG engine should last longer.

UPS plans to buy another nine LNG tractors, according to Jill Reece, Pacific Region automotive manager. A "wish list” of changes, she said, includes more power and an electric driveline retarder. Mack diesels in UPS' linehaul tractors are set to 355/385 hp, making the LNG's 350 hp a little wimpy. And the diesels have Jake Brakes, which cannot work with the LNG engines.

The P-1000 (for package, 1,000-cubic-foot capacity) walk-in van has a General Motors 4.3-liter V-6 gasoline engine converted to burn compressed natural gas. One was on display and another available for driving. These "package cars" are Class 5 trucks originally built with Onan diesels, and are among a group of 145 based in the Los Angeles area that were retrofitted with the 122-hp CNG engines.

CNG is stored under 3,000-psi pressure in two 16-gallon tanks; a regulator cuts pressure to about 35 psi before it goes to a pair of throttle-body injectors on the engine. As with LNG, range with CNG is limited; the 32 gallons lets one of these cars run 100 miles, less than half the range of a diesel-powered car.

For some reason, the engines' spark plugs become fouled at 20,000 to 22,000 miles and are replaced, said Robert Hall, a corporate maintenance manager. And pressure regulators tend to fail at about 25,000 miles. GM has worked on both problems, and the second generation of CNG engines should be better.

Little or no soot goes into the crankcase, so the oil change interval is stretched from a gasoline engine's 3,000 miles to 4,500 miles, said Al Freilich, a Los Angeles-based fleet manager.

Driving a P-1000 is more a handful than it may appear. The "car" is rather bulky. Steering is unpowered and slow, so you have to really crank through corners. The mirrors and big windows give a good view of what's around you; if the weather's decent, you can leave the sliding doors open for an even better view.

The P-1000's CNG engine behaves a lot like it still burns gasoline. But of course it makes no fumes and, Freilich said, is a bit quieter. One weird noise is an occasional moan that comes from the gas regulator; to me it sounded like a vibrating steel panel.

He pointed out the engine can be lugged quite low, which is useful in traffic. With only 122 hp and a 4-speed transmission, it's less than a sparkling performer, but is enough for tooling around the mostly flat city.

By the way, later package cars have 210-hp diesels with 5-speed transmissions. The engine is either the Cummins B5.9 or the International T444E, depending on whether Freightliner or International built the chassis.

UPS has a firm rule about starting out in Low no matter what; this is easy on the clutch, if a little more work for the driver. If you're rolling, you can use the next higher gear. The latest package car specs include an Allison 5-speed automatic, which must be like heaven for a UPS driver.

Much quicker than any of them is the Chrysler-built electric-powered Dodge Caravan. Its electric motor replaces the stock V-6 gasoline engine and automatic transmission, and a bank of 26 batteries nestles under the floor between the axles. Wired in series, the 12-volt batteries supply 336 volts to the motor.

At the Bibendum, one was for display and another available for test drives. Both look just like a regular Caravan, except, of course, they wear UPS brown paint and are quieter and quicker. The gear selector reads P-R-N-D, and all you do is put it in Drive and zoom.

There is no transmission, so the motor simply winds up as the driver calls for more speed. Jill Reece, the fleet manager, said it would do up to 85 mph, but we held it to only about 60 mph as we roamed around the speedway's grounds.

The instrument panel looks stock, with a large tachometer and speedometer. But the tach turns out to be a current-draw meter whose needle swings around clockwise, climbing fast as you floor the accelerator and dropping as you let up – much like a vacuum "economy" gauge on a gasoline engine. There are two normal-looking small gauges that would register fuel level and coolant temperature on a standard Caravan. But here they show the batteries’ state of charge and temperature.

Batteries have to be kept cool, explained Reece, so the van has air conditioning. Some of its cool air can be run into the cab, so drivers like driving these, she said.

UPS has 13 of the electrovans scooting around downtown L.A. and in the San Fernando Valley, primarily carrying letter packages and other light, compact shipments for early morning deliveries. Each van averages 30 to 35 miles a day. Range is only about 60 miles, and it takes three hours to charge up.

Range should lengthen and charging time shorten as battery technology advances. The A/C fan whirs a bit and the motor whines as it picks up speed. But the electrovan is eerily silent.

Never say never, but unless you go to work for UPS, it's not likely that you'll drive an alternative-fuel rig soon, if ever. Electric power obviously doesn't have the range for long-hauling. "Hybrid" gasoline- and diesel-electric powertrains solve the range problem, but generally lack the stamina needed for climbing long grades and such.

Natural gas works, as the Macks and package cars show. But they are expensive to buy and there are few places to tank up. Truck and engine builders believe that over-the-road rigs will continue to burn diesel fuel for the foreseeable future, though more cleanly. The first of the new diesels with exhaust gas recirculation will appear in a month or two, but that's another story. *