Trash trucks, when it comes to fuel, can be a big waste. The heavy-laden haulers spend most of their days lurching from driveway to driveway at walking speeds. Almost as soon as the engine growls forward from a stop, the driver brakes the truck to a halt again. The engine rarely gets up to optimal speed, and the brakes take a beating.
Garbage trucks have abysmal fuel efficiency, typically around 3 miles per gallon. That is especially bad now, because the price of diesel has stubbornly hovered around $4 a gallon for the last three years. For cities struggling with tight budgets and trying to reduce pollution, garbage trucks are getting closer scrutiny.
So municipal fleet managers -- like their counterparts in private industry -- are taking big steps to cut the costs of taking out the trash. They are looking for savings by switching fuels and by finding ways to burn less of the fuel they have.
The biggest change has been the massive adoption of compressed natural gas -- rather than diesel -- as the primary fuel for new garbage trucks. Municipal fleets and transit systems are increasingly moving to natural gas, as well, but the shift is especially pronounced in waste trucks.
Only about 10 percent of U.S. refuse vehicles (including both public and private fleets) run on natural gas, but half of all new purchases are for natural gas trucks, said Jeremy O’Brien, the director of applied research at the Solid Waste Association of North America, a group of public waste removal agencies.
Private companies such as Waste Management and Republic Services are buying thousands of new natural gas vehicles. The public sector is lagging behind private haulers in making the switch, because governments have a harder time finding the large amounts of money needed to buy the new equipment, O’Brien said. But cities and other local governments are moving in the same direction.
Natural gas trucks can save on fuel costs, but the up-front costs are significant. The priciest component is installing a natural gas fueling station, which depending on its size, can cost up to $2 million. A fleet’s maintenance facilities have to be upgraded to prevent stray sparks from igniting an explosion. The trucks themselves can also cost $30,000 more than their basic diesel counterparts (pollution controls can also add costs to diesel trucks).
But the savings for natural gas vehicles add up quickly. Natural gas prices have plummeted since the widespread use of hydraulic fracturing, or fracking, has unlocked huge reserves of natural gas throughout the United States and Canada. The average price of a diesel gallon equivalent is about $2.11.
And, in some places, garbage trucks can run on the methane captured from the same landfills where they drop off their payloads. Bacteria breaks down organic waste to produce the methane, which is then filtered and compressed for use in the trucks.
“You get what we call a triple bottom-line benefit: people, planet, profit,” said Geoff Apthorp, vice president of engineering and business development at Environmental Solutions Group, a solid waste equipment company.
Hybrid vehicles can also reduce fuel costs and greenhouse gas pollution. The idea is to capture the energy that is normally lost when the garbage trucks brake, store it and use it to propel the truck later. With all the stops their routes, garbage trucks are especially well-suited for those technologies.
So far hybrids are only used by a handful of cities, because the technology is still being honed. Electric hybrids, for example, require batteries that would be so heavy they could offset the fuel savings.
WATCH: Cleaner Trash Trucks
Miami-Dade County, though, has been using hydraulic hybrids for the last four years. The trucks, which store energy using liquid tanks, use a diesel motor to charge the tanks when the truck is first turned on and also to travel at speeds faster than 45 mph. Once the truck is moving, though, brake energy is stored in the tanks.
What that means is that during the stop-and-start pickup cycle, the trucks run mainly on stored brake energy. Danny Diaz, the fleet manager for the county’s Public Works and Waste Management department, said the hybrid trucks reduce fuel consumption by 40 to 45 percent. “That’s any eye opener for anybody in this line of business,” Diaz said.
The hybrids also save money on brake replacements. The brakes on garbage trucks usually must be replaced several times a year, but the hybrids, because they use a separate braking system to recapture energy, only need replacements once in the life of the truck, which is usually about seven years.
Thirty-five of the county’s 200 side-loading garbage trucks are now RunWise hybrids, which are sold by Parker Hannifin. “It’s not new technology anymore for us,” Diaz said. The Parker hybrids are also used by the cities of Miami, Orlando and Tacoma, Washington, among others. The company is also developing a hydraulic hybrid that uses natural gas instead of diesel as its second fuel source.
Miami-Dade County received several guarantees from Parker when the county bought the first hybrid prototypes, Diaz said. But O’Brien, the SWANA researcher, said local officials typically shy away from new technologies. “Nobody wants to be the first on the block to try them, especially in local government,” he said. “They’re not paid to take risks.”
Instead, O’Brien said, public waste haulers are finding simpler ways to save money. “You can conserve fuel by more efficient technologies, but you can also conserve it by narrowing the types of services you offer and the frequency,” he said.
That means using the same type of trucks to haul garbage and recyclable materials. Some cities, like Indianapolis and Houston, are developing systems that would collect garbage and recyclables together and separating them before they get to the landfill.
Manufacturers can also decrease fuel use by making their trucks lighter, as ESG Group did with its latest model of Odyssey trucks, said ESG’s Apthorp. Versatile, automated trucks also save money on staff costs and increase safety, he said. The cost savings also increase when fleets rely primarily on one type of vehicle, he said.
“If you have a uniform fleet,” Apthorp said, “you get greater productivity out of your operators and your maintenance people; less inventory; (and) greater utilization of those trucks.”