PHOENIX – Now that hybrids have a firm green foothold on the market for cars and light trucks, they are moving into medium- and heavy-duty trucks. And while they are still expensive, they are getting more economical by the day as diesel prices continue at or near record levels, according to The Arizona Republic.

Just about every manufacturer of medium- to heavy-duty trucks, including majors like Freightliner LLC, Navistar International Corp., Kenworth Truck Co., and Peterbilt Motors Co., are developing or producing larger hybrid diesel-electric trucks, according to Robert Clarke, president of the Truck Manufacturers Association in Washington, D.C. Several companies began producing them this year.

Hybrid diesel-electric trucks are expensive, but manufacturers say the vehicles can save 30 to 60 percent on fuel costs, depending on how they are used. They also reduce diesel emissions and should help quiet truck and bus noises. Dealers expect the costs to come down in time.

Clarke said the diesel-electric technology is ideal for delivery and garbage trucks and buses and other stop-and-go urban uses because the more the vehicles stop, the more their batteries get charged. The technology has been around for some time, but mostly for mining and military uses. Like cars, hybrid trucks rely more on electric power at low speeds.

Some say that a diesel-electric bucket truck could reduce its idling time by 85 percent and save up to 60 percent in fuel. But, so far, the diesel-electric hybrids cost up to 60 percent more than a comparable diesel-only truck.

One big advantage the hybrids offer is that they are quieter because they can idle on electric power. Electric motors could be used when workers are lifted in buckets to work on power lines or streetlights, according to The Arizona Republic.

The diesel-electric hybrids are just one of the green options at which manufacturers are looking. In addition to making regular diesel trucks more efficient, less polluting and quieter every year, they are starting to look at producing hydraulic diesels and trucks that use liquefied natural gas instead of diesel.