In the early 1990s, Toyota Motor Corp. decided that the then unappreciated concept of powering a vehicle with both a conventionally fueled mechanical engine and a battery-powered electric drive system had a role to play in passenger transportation. A few years later, the company released its first hybrid car model and forever changed the way the world views alternative propulsion.
As the idea of hybrid-electric engines gained attention in the automotive market, the technology also slowly caught on with the transit industry. Today, an estimated 700 hybrid-electric buses are operating revenue service in the U.S. and Canada, with 400 more scheduled for delivery. Countless more agencies are giving serious consideration to these promising vehicles.
While the growth in popularity of hybrids has been undeniable, dozens of questions remain, and scores of potential buyers are attempting to weigh the benefits against the still excessive upfront costs. In an operating environment where fuel costs, emissions requirements and government funding continue to be erratic, hybrid-electric propulsion offers an intriguing mix of solutions and challenges to the public transit industry.
The fiscal case for hybrids Conversion of unused energy to usable energy. Stored kinetic energy that is not used, such as heat during brake usage, can be converted back into useful power by high-tech energy storage units, which function like a generator.
Integration of other onboard equipment. A hybrid-electric powertrain can also be used to power and integrate all other types of electrical equipment — entertainment systems, lighting, etc. — through one energy source.
Quieter rides. When hybrids operate on electric power, there is very little engine noise, making them ideal for late night or early morning routes.
A greener technology?
Hybrid-electric technology has grown significantly in the transit industry over the past five years. What was once a one-player market now has a half-dozen suppliers, and more are on the way. With this continual saturation of hybrids into public transit, the Federal Transit Administration (FTA) sponsored a study this year to examine “the state of electric drive technology for transit buses; the benefits of major market penetration of electric drive buses to transit; and the barriers that remain to achieving this goal.”
The study, which was conducted by the Northeast Advanced Vehicle Consortium (NAVC) and released last August, drew its conclusions from interviews with representatives of transit agencies, private bus companies, hybrid system developers, engine manufacturers and research organizations. Results of the study paint a generally favorable portrait of hybrids but indicate that capital costs for a hybrid are approximately 60% to 80% higher than a comparable diesel-fueled bus.
“Right now, you don’t purchase these buses for the cost savings,” says Chris Collet, product sales manager for GM-Allison Electric Drives, which has manufactured hybrid propulsion systems for more than 360 buses currently in service. “You do it for other reasons.”
Like all new technologies, hybrids are still very expensive, due in large part to the costly high-voltage electric drive and advanced battery packs. According to the NAVC-FTA study, hybrid-electric vehicles cost, on average, between $170,000 and $250,000 more than conventional diesel buses.
But this is a price that should come down as competition intensifies, more suppliers enter the market and production levels increase. Additionally, study respondents suggested that capital costs might decrease and more agencies could get their hands on the technology if the FTA began a hybrid-specific federal funding initiative.
Furthermore, Collet says that the outlook for more funding for hybrids in the transit industry is very bright, particularly because it will make legislators look good to constituents. “From a public policy standpoint, the congressional people really seem to want to help fund this technology,” he says.
Ultimately, the biggest determining factor in whether capital costs become more manageable might be the acceptance level and feedback provided by those agencies that have already incorporated hybrid buses into their fleets. “We were fortunate that King County Metro in Seattle bought a large number of hybrids and a portion of conventionals at the same time,” says Collet. “It gives a great perspective on how these buses measure up.” And so far, he says, the hybrids have performed very well.
The lifecycle dilemma
Despite the higher initial cost, no one disputes that hybrid-powered buses offer tangible benefits over other types of propulsion systems. Though it is still too early to draw any definitive conclusions, manufacturers and operators of hybrid buses tout significant savings in several areas. The primary source of savings
is in fuel.
“What is interesting about hybrids is that the initial driver of the technology was in emissions and air quality improvements, but that has changed to fuel economy,” says Tom Webb, business development manger for the transit bus division of BAE Systems, a global provider of transportation technologies. “With diesel fuel reaching $3 a gallon, hybrids at today’s price are becoming much more cost effective on a lifecycle basis.”
Still, the NAVC-FTA study declared that the price premium for hybrid buses will not be offset by fuel savings alone over the life of the bus. But with energy experts almost unanimous in their claim that petroleum-based fuel prices will continue to rise, this may not always be the case. Additionally, hybrid supporters cite a host of other cost reductions and performance enhancements that make hybrids competitive on a lifecycle scale.
A series hybrid-electric drive — more common in transit applications than its counterpart, the parallel drive — allows buses to run on electric power at slow speeds, such as those often encountered in fixed, urban routes, resulting in a smaller fuel consumption. Moreover, says Webb, these buses can be implemented into a fleet with no installations or major changes to an operator’s fueling system. “A user gets emissions reductions exceeding clean air regulations without having to change anything about the fuel infrastructure, all while using less fuel.”
There are additional cost savings in maintenance, especially with regard to the powertrain and the brakes. The electric drive, with fewer moving parts, requires far fewer repairs and labor hours. Also, because the electric motor acts as a dynamic brake, when a driver lets up on the throttle, the vehicle automatically slows down. This results in a substantial decrease in the wear and tear on brake friction material, making brakes last far longer.
Real-world experience on hybrid lifecycle costs is extremely limited, as these types of buses have been in revenue service for only two or three years at most. But research and early operator reports indicate that the high upfront premium for hybrids is, at the very least, somewhat balanced by operational and maintenance savings.
Of course, calculating savings on the entire life of a transit bus can be an inexact science. Hybrid-fuel vehicles offer an array of features that are difficult to weigh in dollars and cents. Some of these benefits could prove critical in determining the future of this technology.
Improved acceleration is one of these features. “This system has a lot more torque than is needed, and even though we don’t necessarily supply it — a bus is not a hot rod — these buses will function better in certain environments,” says Webb. “They are great in San Francisco, for example, because hybrids are the best hill climbers outside of a trolley bus.”
GM-Allison’s Collet says that this increased power also allows buses to merge into traffic faster and finish routes in less time. This leads to more efficient route scheduling and on-time performance. “Further down the line, you can start looking at better farebox recovery and possibly even needing fewer buses,” he adds.
Another corollary of better perfomance is driver and rider satisfaction. Collet says that feedback from drivers who operate hybrids reveals that they are happier because they can finish their routes faster. Also, because of the electric motor’s deceleration function, drivers perform most of their operating duties directly off the throttle pedal. “They don’t have to move their leg and foot as often from the brake to the accelerator, so we are expecting to see a reduction in knee and ankle injuries to drivers,” he says. Collet notes that riders seem to gravitate to hybrids because of their reputation for being cleaner and faster.
Other benefits that could potentially result in hidden cost savings include:
One thing is clear. The quest to explore hybrid technology in transit vehicles began with a desire to reduce pollution.
“As frustrating at times as ever-increasingly stringent air quality regulations can be to an industry, both users and suppliers, there is no doubt that in the U.S. we wouldn’t be leading the way to develop new, cleaner technologies if it wasn’t for the environmental regulatory agencies raising the bar and challenging everyone to get there,” says Webb.
Webb says that in Canada, for instance, there has been a rapid adoption of hybrid technology because the nation signed the Kyoto Protocol, which calls for reductions in greenhouse gas emissions. However, in the U.S. at present, the Environmental Protection Agency’s (EPA) forthcoming emissions regulations for transit only apply to engine out emissions, which hybrids do not affect. The EPA standards don’t say anything about tailpipe emissions, an area greatly improved by hybrids.
Currently, the California Air Resources Board (CARB) is the only air quality regulatory agency that gives any official credit to hybrid buses. With CARB calling for a blanket 25% reduction in NOX emissions, end users in California can exceed those emissions reductions standards with hybrid buses. Not coincidentally, several agencies in the state are either operating hybrids already or in the process of purchasing them.
As far as how the failure for regulatory agencies to address hybrids is affecting sales of this technology, Webb says that, regardless of what the law says, no agency would buy a hybrid vehicle if it wasn’t motivated in part to put a cleaner product on the street. “You can put a regular clean diesel on the street, and by law that is all you have to do,” he says. “But anyone contemplating something clean, whether it’s CNG or hybrid or whatever, is interested in the soft side, as well as a better public image.” And hybrids, he says, certainly offer this.
Obstacles to implementation
The drawbacks appear to be few, but there are some significant questions about hybrid technology. Probably the biggest concern, as indicated by the NVAC-FTA report, is the life and stability of energy storage systems. With the relatively short history of hybrids in operation, little is known about battery life, but there are indications that it may be disproportionately short. What is for sure, however, is that battery replacement in a hybrid will represent a huge maintenance cost.
One answer to this dilemma is the emerging technology of ultracapacitors. An ultracapacitor is a storage device that replaces the energy of chemical batteries. This technology is what allows potential kinetic energy to be stored and used later for acceleration or powering equipment.
“Ultracapacitor-based systems achieve higher fuel economy than comparable battery-based systems because they are more efficient in absorbing braking energy and do not require air conditioning,” says David Mazaika, president of ISE Corp., which manufactures hybrid-electric drives for transit buses, as well as a line of ultracapacitors. “They are also projected to perform reliably over hundreds of thousands of discharge-recharge cycles, which equates to years of maintenance-free service.”
Another, much smaller concern involves the handling of a high-voltage system onboard the bus. While all necessary precautions have been taken to prevent any electrical danger, the amount of voltage alone can be a cause of some worry for operators. When you are dealing with this kind of voltage, says Webb, there is an inherent worry among drivers and maintenance workers that you have to alleviate through training. “As manufacturers, we have worked very, very conscientiously to design in the various protections, warnings, enclosures, voltage detections, disconnects, labels and all the other safeguards necessary,” he says.
As for training and infrastructure, hybrid vehicles require very few changes to existing practices. According to Collet, the actual new equipment training for drivers typically lasts all of five minutes. He also says the increased usage of hybrid technologies in passenger cars is helping push forward this technology in the transit industry. “We went out to do a demo of these buses in Aspen, Colo., and the people already seemed to know everything they needed to know about hybrids.”
The Nuts and Bolts of a Hybrid
1. Two hybrid control modules. Act like the brain by processing information from the other system components and driver inputs.
2. Energy storage unit. Supplies energy to the electric motor. Allows for a reduction in fuel consumption, emissions and noise.
3. Range selector. Allows driver to select the operating range (forward, reverse, neutral, etc.)
3. Dual Power Inverter Module (DPIM). Converts electrical energy into alternating current or direct current. The storage unit stores direct current, while the electric drive uses alternating current for power.
5. Electric drive. Acts like a transmission. Regulates variable operating range between electric motor and the engine.