SOLAR TODAY - April 2010

sustainable transport

CL

Connect with author Seth Masia on the SOLAR TODAY blog: solartoday.org/blog

intention to double the efficiency of their truck
fleets by 2020.
part of this improvement will be due to chang-
es in the tires, engine and transmission. Michelin
has taken the lead in developing low-resistance
tires, claiming that a 3 percent improvement in
rolling friction yields a 1 percent improvement
in fuel mileage at highway speeds. By using more
sophisticated transmissions, truckers can more
accurately match engine speed to the load and
get by with 250-horsepower engines instead of
the 500-hp diesels now considered standard for
Class 6 tractor-trailer work. Better yet, there’s a
realistic prospect of replacing some of the diesel
fuel with a cleaner, cheaper alternative: liquid
natural gas (lNG). Kenmore, peterbilt, Mack,
international and Volvo are among the truck
manufacturers road-testing mixed-fuel engines.
These models start using diesel fuel and then
flow lNG into the intake stream so that only a
trace amount of diesel is needed on each injec-
tion cycle to ignite the air-fuel mixture. lNG has
only 60 percent of the energy density of diesel,
but it currently sells for half to one-third the cost
of diesel and burns with roughly 60 percent the
carbon and particulate emissions. Several dozen
mixed-fuel trucks are now in regular commercial
service in North america and Europe to test
the concept. a big advantage: Where lNG isn’t
available, you can still run on pure diesel.
a study by Hiroko Kawai at the rocky
Mountain institute (rMi, rmi.org) suggests that
incremental improvements in trucks can push
over-the-road efficiency up to 12. 5 mpg and
275 tmg. Where state regulations permit, Kawai
found, a tractor can haul two or three trailers in
a “road train,” doubling or tripling tonnage at no
aerodynamic cost. Fuel use declines to 8. 7 mpg,
but efficiency improves to as much as 335 tmg.
at this point, operation of the truck begins to
resemble railroad logistics. Near its destination,
the road train has to pull into the equivalent
of a switching yard so it can be broken up into
single-trailer rigs for local delivery.

in terms of fuel use, local delivery is the least efficient mode of trucking. Constant starts and stops in traffic and at many daily destinations mean delivery vans, like garbage trucks and city buses, get 4 to 10 mpg and may pull 20 to 50 tmg or worse. like garbage trucks, utility company trucks and buses, they are prime candidates for hybrid gas-electric, diesel-electric or

railex

plug-in hybrid drive. Electric companies, the U.S. postal Service and UpS have been testing hybrid delivery vans for some years, and their numbers are now in the thousands. The technology will soon be standard for stop-and-start transport modes.

roadway improvements needed
acceleration and braking are the big energy
hogs in transport. at rMi, Hiroko Kawai points
out that the driver who can keep a steady speed,
and minimize engine revs, will always get better
mileage and lower maintenance costs. Speed
changes, however, are very much dependent on
infrastructure and traffic. airplanes and ships at
sea, for instance, can accelerate to cruise speed
and rarely have to slow or divert around other
traffic. Traffic flow becomes an issue only where
it funnels to a limited infrastructure resource —
a runway or a port entry.