The Green Machine

Emergency response vehicles represent one of the most significant costs for local governments. Most agencies demand 24-hour coverage, requiring long service hours for vehicles. The need for immediate response dictates that vehicle’ engines be prepared for high performance without advance notice. Because of this, in some parts of the country during cold-weather months, diesel engines may be kept running in idle between calls throughout an entire shift. Other agencies keep diesel engines idling during calls and in hospital bays because idling doesn_t damage the diesel engine.

These practices reduce fuel efficiency, increase pollutants and adversely affect health.1-2 In addition, driving patterns that optimize transport time during emergency response correlate with the poorest fuel efficiency: rapid starts and stops, high speeds, and extended idling while patients are receiving field care.

The opportunity exists, however, to improve this situation by exploring alternative power plant or fuel sources, especially for quick response vehicles (QRVs) that generally carry personnel or equipment rather than patients. With this in mind, staff at Burke County (N.C.) EMS undertook a study in November 2005 to see how well a mid-size hybrid electrical-gasoline SUV would perform as an”žEMS vehicle.

We had a number of specific questions. Mid-size SUVs are more efficient than large SUVs, but would they have enough cargo space? Could hybrid engineering support the electrical needs of an EMS vehicle–for example, lights and sirens? Was the hybrid engine reliable enough for emergency responses, and would it operate as well as a traditional vehicle in the rugged EMS environment?

We also customized our study vehicle for operation on our wilderness EMS (WEMS) team. WEMS systems are well described elsewhere and seemed to be ideal for high-efficiency vehicles.3-5 The study vehicle was a personal vehicle used part-time for EMS and WEMS activities by the assistant medical director.

So can an EMS system realistically and affordably switch to alternative fuel or hybrid technology to develop a high-efficiency, low-polluting QRV for use in EMS? And is it economically desirable? The answer to both may very well be yes. Our study suggests that partial zero-emission hybrid vehicles would be less expensive to purchase and operate, and substantially less damaging to the environment.

Why fuel efficiency & global warming are relevant to”žEMS
We’re all aware of record fuel prices, political and strategic concern about dependence on foreign oil, dire warnings about global warming and growing environmental consciousness. It’s no surprise then that fuel efficiency and greenhouse gas emissions are high-profile topics. President George W. Bush announced an executive order in May 2007 instructing federal agencies to Ë™cut gasoline consumption and greenhouse gas emissions from motor vehicles,à“ following Supreme Court instructions that the federal government should regulate these parameters.6

In addition to increased federal attention to this issue, public service agencies at all levels of government are exploring more fuel-efficient and pollution-minimizing options. Advocacy groups are promoting this as well. For example, the Sierra Club_s Cool Cities Campaign calls on cities to sign the “U.S. Mayors” Climate Protection Agreement and make a commitment to reduce global warming. Currently, more than 955 municipalities are Ë™Cool Citiesà“ and many additional counties have signed on as Ë™Cool Counties.”7 Many of the cities have reconfigured their motor vehicle fleet to help accomplish this. Charlotte, N.C., added 21 hybrid vehicles to its city fleet, noting thousands of dollars in savings over the vehicles’ lifetimes due to decreased fuel use and less maintenance.7

These and other pressures have led EMS agencies to examine their environmental impact. Denver Mayor John Hickenlooper has circulated a memo requesting that the city’s Health Paramedic Division “become more ecologically active” in anticipation of the Democratic National Convention being held there in August 2008. In response, Denver switched all of its 35 ambulances to B20 biodiesel fuel, noting reduced carbon and particulate emissions, and public-health benefits associated with reduced diesel-related smog.8

Also, manufacturers may soon be required by federal mandate to improve fuel efficiency for all vehicles. Congress has passed legislation mandating automakers’ entire fleets average 35 miles per gallon by 2020.

If the federal government begins mandating fuel efficiency for your vehicles, or if your mayor becomes interested in having the city sign on as a Cool City, will your administrator be able to respond with sound science about hybrid technology and EMS operations? With rising fuel costs and perennial underfunding of EMS agencies, do more efficient vehicles represent a savings for EMS agencies, or are they inappropriate for our operations?

Choosing the right vehicle class
Gas-guzzling SUVs have generally been used as EMS QRVs because they offer the requisite cargo space for equipment, as well as 4WD and heavy-duty suspension packages necessary for EMS operations.

SUVs are categorized as small, mid-size or large. Small SUVs lack sufficient cargo space for EMS operations, and large SUVs have very poor fuel efficiency. We chose a mid-size SUV because it balanced fuel efficiency with cargo space. However, because large SUVs are more often chosen for EMS operations, one of our study questions addressed the adequacy of a mid-size SUV’s cargo space.

The study vehicle was purchased in”žNorth Carolina, which follows federal standards, but was built to”žCalifornia emissions standards (upon request) at no additional cost. It’s important to note that when this vehicle was purchased in 2005, manufacturers made two versions of most car models: one for sale in states that follow California emission standards and one for all other states. However, dealers will often sell the cleaner version of the vehicle regardless of the state in which it_s purchased, but the consumer needs to ask. Otherwise, an EMS agency purchasing an Escape Hybrid in North Carolina could be driving a more polluting vehicle than an otherwise-identical Escape Hybrid purchased a few states away in”žPennsylvania, which follows California standards.

This situation has stirred legal controversy. The Energy Independence and Security Act of 2007, signed into law by President Bush in December 2007, makes federal vehicle emission standards more stringent, but also makes these standards universal.9 This law prevents California and at least 16 other states from establishing more exacting standards as they have previously done, and, in effect, reduces fuel efficiency in these states.10 California is now suing the federal government, attempting to return this right to the states.11

Choosing the right vehicle“ž
When we set out to purchase a test vehicle in 2005, high-efficiency options in mid-size new model 2006 SUVs were limited to biodiesel fuel or hybrid technology. The 2006 Jeep Liberty offered a Common Rail Diesel (CRD) engine that can operate using biodiesel fuel. The benefits of a biodiesel power system include stronger torque, idling without engine stress and a fuel made from non-petroleum sources.”ž

But we found many drawbacks to a biodiesel power system. Most commercial biodiesel fuel is made from soybeans or rapeseed and requires intensive farming practices, involving petroleum products. Biodiesel fuels are available in a variety of concentrations, but only the weakest are permissible to retain manufacturer warranty. Commercial biodiesel isn’t available in every region, such as where our vehicle was being tested, therefore necessitating out-of-county travel for fueling. Nor is the technology always safe for the environment: Large biodiesel oil spills in”žIowa (2006) and Alabama (2007) have increased local pollution problems.12

Creating biodiesel fuel from reused oil products (e.g., restaurant grease) is also possible, but is labor intensive for the operator, voids the manufacturer warranty and is unlikely to be a sustainable strategy 100% of the time. Given the many inconveniences with obtaining commercial or homemade biodiesel, it’s likely the vehicle would have to be driven at least part of the time using standard diesel fuel. According to the EPA, few SUVs in the country are more polluting than the 2006 Liberty using standard diesel fuel.

In 2005, one mid-size SUV was available offering hybrid technology–the 2006 Ford Escape Hybrid. This vehicle had some performance drawbacks compared with biodiesel-powered vehicles. Torque and pulling capacity were less than standard gasoline-powered vehicles and substantially less than diesel engines, and the vehicle couldn’t idle under gasoline power without stressing the engine.

However, there are substantial benefits to a hybrid power plant. The vehicle can idle in electrical mode with no pollution output or fossil fuel use. In terms of noise pollution, the vehicle operates silently in electrical mode, and when gasoline mode is required, it’s still substantially quieter than a diesel vehicle.”ž

For these environmental and performance benefits, we chose the 2006 4WD Escape Hybrid for our study. It was the second most environmentally clean mid-size SUV out of 189 ranked by the EPA, topped only by the 2WD Escape Hybrid. It scored 9.5 out of 10 for air pollution and 8 out of 10 for greenhouse gas emissions. The Smog Index (0à3 scale) is 0.09.

The additional purchase of 8,000 lbs. of CO2 equivalents annually via TerraPass of San Francisco made this a “carbon-neutral” (or “carbon balanced”) vehicle. This means we applied “carbon balancing,” where CO2 emissions from one activity are offset by the funding (in a calculated amount) of a greenhouse-gas reduction project elsewhere, theoretically canceling out net CO2 emissions. Carbon balancing remains a controversial means of greenhouse gas emission control.13

The fact that the vehicle was made by a domestic manufacturer was also important. Many agencies prefer or are mandated to purchase vehicles made by”žU.S. manufacturersÆ’most commonly Ford, Chevrolet and Chrysler/Jeep/Dodge.

In purely economic terms, as Table 2 (in JEMS) shows, an Escape Hybrid would save an EMS agency 5à18% simply in purchase price alone when compared with standard EMS QRV models.

Minor post-market adjustments were made to retrofit the vehicle for”žEMS and WEMS use, such as the addition of emergency lighting, siren speakers, radio apparatus and a Yakima LoadWarrior rack with axe/shovel bracket on the roof.”ž

Two medical bags, including oxygen, standard paramedic drugs and equipment, a central line kit, and WEMS response gear, weighing a combined 63.5 lbs., were stored in the trunk. A rotating 360-degree Golight Stryker remote-controlled searchlight with cabin and remote joystick controls was also mounted on the front roof, and stationary high beam floodlights were mounted on the Yakima rack.

Power components
The Escape Hybrid has two engines, a four-cylinder gasoline engine and an electric engine. It has a standard 12-V car battery under the hood and a second high-voltage 330-V battery in the trunk (see photo, p. 114), where the spare tire would be located in a standard Escape. (The Hybrid stores its spare tire in the undercarriage.)

The vehicle starts using both gasoline and electrical power, at which point it begins diagnostics to see if it can switch to electrical power only. In the study vehicle, electrical-only power was not possible for the first four minutes, unless it was recently driven.

Once electrical-only power is available, the vehicle idles, cruises at speeds under 40 mph or accelerates at speeds under 25 mph, using 100% electrical power. Any moderate grades or rapid accelerations automatically engage the gasoline engine.

The battery continually recharges from the electric motor (which also works as a generator), kinetic heat energy salvaged from braking (Ë™regenerative brakingà“) and other sources. Speeds over 40 mph engage electric-assisted cruising, when the gasoline engine dominates and the electric engine provides additional horsepower on demand.

Electric engines are good at generating torque at low revolutions per minute (rpms), and gasoline engines are most efficient at high speeds, so this engineering allows each engine to dominate at its most efficient range. Additional technologies also make the gasoline engine and the transmission more efficient than in standard gasoline engines.14

This is known as a “full hybrid,” in which the two power plants can operate independently. A common myth about full hybrid vehicles is that the vehicle must be plugged in to charge, but full hybrids never draw power from an external power source.

Testing performance
The modified Escape Hybrid under study has been in service since November 2005 (27 months) and has logged approximately 25,000 miles. It has been put into operation multiple times for EMS, WEMS and medical support operations. However, the vast majority of that mileage has been spent during commutes and non-emergent travel.

The Escape Hybrid EMS model has averaged approximately 25 mpg city and 27 mpg highway over the study period. (The EPA calculates 30 C 28 H, and Ford calculates 33 C 29 H for this vehicle.) Simple mpg calculations can be misleading, however, as the electric-gasoline hybrid engine operates much more cleanly at the same mpg versus full gasoline and diesel engines. The fuel efficiency drops if the vehicle is driven extensively at speeds over 40 mph (highway), when the electrical engine merely supplements the gasoline engine, or for short drives, because the vehicle can’t run under electric-only power for the first four minutes. This partially explains why this vehicle’s performance has contradicted standard hybrid performance, where city exceeds highway mileage.

The optimal driving pattern for a hybrid would mirror a taxi’s: long or frequent driving episodes at low to moderate speeds with frequent stops. This profile is similar to that of an urban or a suburban QRV during normal non-response operations. The reduced fuel efficiency of this vehicle versus published efficiency values (see Table 2 in JEMS) can therefore be attributed to additional EMS features and emergent response inefficiency (which should be relatively similar across any vehicle chosen). In addition, the driving pattern for this study vehicle most often involved very short distances, negating the electrical benefit. Non-emergent”žEMS driving patterns more often involve longer distances that should more closely approximate published fuel efficiency.

Tracking fuel efficiency could also change driving profiles. With most hybrid vehicles, fuel efficiency is tracked on a dashboard gauge along with rpm (tachometer) and mph (speedometer). This can change driving patterns, such as routes chosen, speed of acceleration and stopping styles, because drivers can see the effects of their actions on fuel efficiency.

Certain WEMS applications yield the highest fuel efficiency. For instance, the vehicle was put into operation providing medical support for a road bicycling event. In this EMS support role in a mountain environment, the vehicle averaged 35 mpg. Although the exact mpg for a non-hybrid vehicle during this kind of event is unknown, the result suggests there are some applications where the fuel efficiency benefits would be particularly high.

Other probable high-efficiency environments include standby operations, command center operations or any other operational environment where the vehicle is traveling at low speeds or on a downhill grade, or idling. The ability to idle under electrical power allows for continuous electrical activity (e.g., illuminating scenes, running lights) with much less engine wear than gasoline engines, offers a vehicle that’s much quieter than diesel engines, and causes less pollution and inefficiency than either. Overall, city driving is usually far more efficient, with no use of gasoline power while idling at stoplights or when traveling under 40 mph.

The performance parameters are ideal for”žEMS use except for its towing capacity, which is its most significant deficit. But the addition of the electrical engine makes the four-cylinder engine much more powerful, with pickup and acceleration more like a V6 or better.”ž

The study vehicle never appeared to be underpowered. It’s a common myth that hybrids are slow or have less acceleration. On the contrary, most hybrids are slightly faster than non-hybrid equivalents. Speed/acceleration is more dependent on the model’s overall engineering than whether it’s hybrid- or gasoline-powered. For example, the Lexus GS450h accelerates from 0 to 60 mph in an impressive 5.2 seconds even though it’s a hybrid (and the comparable non-hybrid models take 5.4 to 5.8 seconds).15

Emergency response on sustained steep grade roadways was the most significant power challenge. This is a common response grade for WEMS vehicles, which regularly respond to SAR or rescue operations at ski areas, climbing areas or parks at higher altitude than EMS bases. But speed of response was never compromised in the study vehicle compared with other responding vehicles.

In summary, Table 2 (in JEMS) demonstrates that a partial zero-emission hybrid vehicle is about twice as efficient as standard EMS QRV models. This means 50% less fuel expense per vehicle in economic terms, and 50% less fossil fuel in environmental terms. It also produces approximately 50% less greenhouse gas.

Vehicle Space: Our test vehicle had 65.5 cubic feet of interior cargo space. The roof rack added additional storage for temporary needs, assuming theft isn_t a concern. By comparison, a 2006 Chevrolet TrailBlazer has 80 cubic feet of cargo space, and a 2006 Ford Explorer has 86 cubic feet (see Table 3, p. 118 in in JEMS).

Space was never a problem during”žEMS operations. On rare occasions when large cargo was required, the roof rack was used without difficulty. This calls into question whether the additional 15à20 cubic feet of cargo space is operationally necessary and proportionately beneficial given the significant sacrifices it represents in emissions and fuel efficiency. Other agencies have also found that fielding smaller response vehicles results in savings without a loss of function.16

Electrical Power: One question frequently raised is whether hybrid technology can support the additional electrical systems on an EMS vehicle, such as lights, sirens and radios. This represents a misunderstanding of hybrid technology, which actually provides more electrical power. In fact, the study vehicle was equipped with a 110-V/

150-watt standard AC outlet to access this additional electrical power (see photo, p. 112). Our vehicle supported a standard emergency light and siren system without difficulty. Ford engineers believe a failure of the high-voltage system (discussed on p. 118) was not related to the emergency systems electrical load.

Noise Pollution: A final performance parameter to consider is noise pollution. At a working trauma scene, for instance, multiple vehicles are present and idling. Many of them are diesel-powered and extremely loud, and contribute to the complexity of scene management. Converting some of these vehicles to hybrid power plants could substantially reduce ambient noise levels. This was experienced and commented upon many times during the study period. Hybrid vehicles can idle in electrical power for substantial periods without any deficiency in running lights, radios, etc. Periodically, they cycle back into gasoline power for a few minutes to recharge the batteries, and then resume electrical operation automatically.”ž

Reliability & maintenance
Within the first 12 months, the high-voltage battery and the antilock braking system failed and required replacement. Both were covered by warranty.

A common myth about hybrids is that the high-voltage battery will need to be replaced at a cost of $5,000à$8,000. Although this price range is roughly accurate, unlike regular car batteries, engineers don_t intend for these batteries to ever be replaced during the life of the vehicle. As of 2006,Toyota claimed to have never replaced a high-voltage battery except as a result of collision damage.17

Therefore, this battery failure appears to be highly unusual, but it served well in testing the warranty. Manufacturers are required to warranty their high-voltage batteries for 10 years or 150,000 miles in states that follow California standards and eight years or 100,000 miles in states that follow federal standards.18

The reliability of the hybrid system must be considered in the context of the reliability of current EMS vehicles. For example, our service also uses Ford ambulances. During the study period, these ambulances averaged at least one episode of unplanned maintenance or failure each, resulting in complete loss of service. In addition, two ambulances sustained complete loss of vehicle function in the first 60 miles or 24 hours of operation due to engine failure. Therefore, the study vehicle appears to be at least as reliable as other vehicles currently utilized by the same agency.

The only routine maintenance found to be more expensive for the hybrid was in replacing oil filters. An Escape Hybrid oil filter retails for $44.22, whereas a regular Escape oil filter retails for $17.58. This could be a moderate cost increase for a fleet of hybrids, and is significant for WEMS vehicles, which frequently drive on dirt/gravel roads and may require more frequent oil filter changes than urban or suburban response vehicles. Be sure to include this in cost projections.

Other vehicles & fuel sources
The Toyota Highlander is now available with a hybrid engine. The EPA classifies this vehicle as a mid-size SUV, but it’s substantially larger, less fuel efficient and not configured for true off-road performance. Nonetheless, it could be attractive as an EMS option.

Mercury now produces a Mariner Hybrid, a vehicle identical to the Escape Hybrid with slight luxury changes and the Mercury emblem. In 2008, Chevrolet introduced a hybrid version of the Tahoe. For agencies that find a mid-size SUV doesn’t offer sufficient cargo space or power, this large SUV still benefits from hybrid technology and is built by a domestic manufacturer.

Chevrolet also offers an extensive line of flexible-fuel vehicles (FFVs), marketed as “FlexFuel,” allowing for the use of E85 ethanol. Many government fleet vehicles now use this technology in response to pressures for more environmentally sensitive operations. Also, 20 demonstration models of a Ford Escape Hybrid E85 have been built.21 However, E85 is, in fact, less fuel efficient than standard gasoline, and questions have been raised about its limited availability, higher pump cost and indirect effect on increased gasoline consumption.22

Biodiesel continues to be an appealing option. Diesel engines don_t have the deficits in towing capacity and power seen with electrical-gasoline hybrids. Most ambulances in operation already utilize diesel engines, suggesting that conversion to a biodiesel fuel source wouldn_t require any significant changes in existing vehicle fleets.

Many fleets have pursued this option. The entire Great Smoky Mountain National Park diesel fleet now operates exclusively on either 20% or 50% biodiesel. Sustainable conversion to biodiesel would depend on a reliable biodiesel source, assurance from manufacturers that biodiesel use wouldn’t void warranties, and biodiesel source materials that don’t require extensive petroleum fuel or disproportionate land use for refining.

Many other alternative fuel sources, power plants and fuel-efficiency measures have been discussed and may become options for”žEMS in the future. Biofuels made from sources other than corn-based ethanol include methanol; cellulosic ethanol from waste woods; ethanol from switchgrass, sugar or beets; or even algae-based ethanols.

Other possible technologies include 100% electrical vehicles, vehicles powered or supplemented by photovoltaic (solar) electricity, waste vegetable oil biodiesel fuel, ethanol-diesel fuel mixtures, Ford’s Clean Diesel Technology (introduced with the 2008 Super Duty diesel, which reduces particulate output by 96%, a level equivalent to gasoline engines) and basic fuel-efficiency interventions, such as aerodynamics and engineering advances.

The White House has been a proponent of funding the development of fuel-cell technology, although some studies suggest it’s no better than available hybrid technology.19

Hybrid electric-gasoline vehicles may be appropriate for EMS vehicles in some operational environments. Our study vehicle performed traditional”žEMS and WEMS activities without difficulty during the two-year study period. Based on published specifications,”žpartial zero-emission electric-gasoline hybrid vehicles such as this could be approximately 10% less expensive to purchase, operate at approximately half the annual fuel costs, emit approximately 50% less greenhouse gas and be inexpensively carbon-balanced. However, they offer less carrying and towing capacity than traditional QRVs.

Our study suggests that more research is indicated on full-time QRV hybrid vehicles. Another critical area requiring research is mechanisms for blunting the environmental and public-health impact of diesel EMS vehicles, as diesel is the most common fuel source for large EMS vehicles.

It appears that”žEMS vehicles can and should be operated with much higher fuel efficiency and much lower environmental impact. Because of multiple pressures, EMS will likely need to consider the fuel efficiency and environmental impact of its operations. Some improvements can be free, such as changing driving patterns and requesting that vehicles purchased be built to California emission standards. Further improvements in EMS environmental impact and overall fuel efficiency could include more powerful and efficient hybrid engines, more vehicles with hybrid options, more pervasive use of hybrids in”žEMS fleets, and more availability of alternative fuels and engine systems.

Study Limitations: This study evaluated a privately owned, part-time EMS QRV involved primarily in WEMS operations in a rural/small-town environment. Its operational profile is clearly different than a full-time EMS QRV or ambulance. The study addressed only a single vehicle rather than an aggregate fleet.

Acknowledgements: The study has been endorsed and supported (non-financially) by the Green EMS Initiative, a project of The Appalachian Center for Wilderness Medicine.

The author extends appreciation to the following individuals and agencies that have supported this study with non-financial assistance: Burke EMS Special Operations Team, Joey Autrey, Martin/Crossroads Family Ford, Greg Huntley and Richard Trosdal.


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  11. KTVU News: Ë™California sues EPA over auto emissions standards.à“ Nov. 8, 2007.”ž
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  13. Smith K: Ë™The carbon neutral myth.à“”žAmsterdam, The Netherlands: De Wittenstraat 25, 2007.”ž
  14. Grabianowski E: Ë™How Stuff Works: How the Ford Escape Hybrid Works.à“”ž
  16. Ë™Mesa FD fields smaller units for non-emergency calls.à“”žBest Practices in Emergency Services. 11(3):1, 2008.
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