Hybrid vehicles can provide roughly $2,000 in fuel savings and cut greenhouse gas emissions by up to

12 metric tons per year, when used in stop-and-go freight applications like parcel delivery.

What is the challenge?

Energy losses during deceleration and braking can

be significant, especially in vehicles that frequently

stop or slow down, like trucks operating in urban

areas. In addition, many freight trucks operate under

conditions that require a wide range of engine

performance. Engines designed to perform across a

wide range of operating conditions tend to be less

efficient and larger than engines designed to work

within a less demanding range. Engine size generally

affects the size and weight of other vehicle

components, such as the radiator. Taken together,

the energy losses due to braking, and the extra fuel

consumed by less-efficient engines and heavier

vehicle components can account for 30 percent or

more of a vehicle’s total fuel use.

What is the solution?

Hybrid powertrain technology makes it possible to

optimize engine size and efficiency, and capture and

harness the energy lost during braking. Hybrid

vehicles have two propulsion power sources. The

main power source is usually a conventional internal

combustion engine. Energy recaptured from braking

is converted and stored until it can be reused by the

second power source. The second power source

generates extra power to supply “boost” to the

vehicle when needed - for example, to climb a hill or

accelerate to pass. Because the main engine no

longer has to handle the full range of power

demands, it can be optimized to operate within its

most efficient performance range. Engine

optimization generally allows the engine and related

components to be downsized as well.

There are a variety of hybrid powertrain designs. In

one design, the second power source is an electric

motor/generator, and the recaptured energy is stored

in a battery. However, batteries are generally heavy

and slow to charge. A variant of this design stores

the energy in ultracapacitors, which are lighter and

charge quickly, but are costly. A third design stores

energy as hydraulic pressure. Hydraulic fluid inside a

sealed cylinder pushes against a “bladder” of inert

nitrogen gas, which is compressed and thus stores

energy. Hydraulic systems can charge and discharge

energy quickly, and may use a pump motor/generator

as the second power source. Other hybrid designs

use flywheels to store energy.

Although the first commercial applications of hybrid

powertrain technology have been in passenger

vehicles, it is more efficient to put hybrid technology

on heavier vehicles like trucks. This is because a

vehicle with greater mass requires more power to

stop it, which represents more potential energy that

can be recaptured during braking or deceleration.

Larger vehicles tend to have more available space

for packaging the hybrid powertrain components.

Heavy-duty trucks typically cost more than passenger

vehicles, so the additional cost for the technology is

a smaller percent of total vehicle cost.

The results are in . . . 

In pick-up and delivery service, truck fuel economy

can be improved from 30 to 50 percent using hybrid

powertrain technology, depending upon the type of

technology and the amount of energy that can be

captured from braking and deceleration and then

reused. A typical step van could save as much as

$1,200 in fuel costs and reduce greenhouse

emissions by more than 7 metric tons per year.

Benefits for a typical enclosed delivery van truck

would be greater – at least $1,900 in fuel savings and

12 metric tons of greenhouse emissions per year.

Next steps

Fleets that operate primarily in urban areas or in

stop-and-go applications should consider using

hybrid vehicles. Transit bus, garbage truck, parcel

delivery truck, airport parking shuttle van, and utility

truck fleets could all potentially save fuel by using

hybrid technology. Companies interested in learning

more about hybrid technology and its potential to

improve the fuel economy of their fleets may visit the

Internet sites of the Environmental Protection Agency

(www.epa.gov/otaq/technology.htm) and the

Department of Energy (www.ott.doe.gov). Numerous

other web sites provide information about various

public and private organizations that promote and

develop hybrid truck technology. Trucking companies

can also learn from the experience of others in the

freight industry. For example, at least two major

parcel delivery companies are exploring the use of

hybrid technology for step vans in commercial fleets.

In May 2003, FedEx Express publicly announced it

would test twenty hybrid electric trucks for potential

use in its pick up and delivery fleet.