3.4.4.8 Waterborne Transport
Opportunities for reducing energy use and GHG emissions from waterborne transport
were not covered in the SAR. The predominant propulsion system for waterborne
transport is the diesel engine. Worldwide, 98% of freighters are powered by
diesels. Although the 2% powered by steam electric drive tend to be the largest
ships and account for 17% of gross tonnage, most are likely to be replaced by
diesels within the next 10 years (Michaelis, 1997). Still, diesel fuel accounted
for only 21% of international marine bunker fuel consumed in 1995 (Olivier and
Peters, 1999). Modern marine diesel engines are capable of average operating
efficiencies of 42% from fuel to propeller, making them already one of the most
efficient propulsion systems. The best modern low-speed diesels can realize
efficiencies exceeding 50% (Farrell et al., 2000).
Fuel cells might be even more efficient, however, and might possibly be operated
on fuels containing less carbon (Interlaboratory Working Group, Appendix C,
1999). Design studies suggest that molten carbonate fuel cell systems might
achieve energy conversion efficiencies of 54%, and possibly 64% by adding a
steam turbine bottoming cycle. These studies do not consider full fuel cycle
emissions, however. Farrell et al. (2000) estimated the cost of eliminating
carbon emissions from marine freight by producing hydrogen from fossil fuel,
sequestering the carbon, and powering ships by solid oxide or molten carbonate
fuel cells at US$218/tC, though there is much uncertainty about costs at this
time.
A number of improvements can be made to conventional diesel vessels in, (1)
the thermal efficiency of marine propulsion (5%–10%); (2) propeller design
and maintenance (2%–8%); (3) hydraulic drag reduction (10%); (4) ship size;
(5) speed (energy use increases to the third power of speed); (6) increased
load factors; and (7) new propulsion systems, such as underwater foils or wings
to harness wave energy (12%–64%) (CAE, 1996). More intelligent weather
routing and adaptive autopilot control systems might save another 4%–7%
(Interlaboratory Working Group, Appendix C, 1999).
3.4.4.9 Truck Freight
Modern heavy trucks are equipped with turbo-charged direct-injection diesel
engines. The best of these engines achieve 45% thermal efficiency, versus 24%
for spark-ignited gasoline engines (Interlaboratory Working Group, 1997). Still,
there are opportunities for energy efficiency improvements and also for lower
carbon alternative fuels, such as compressed or liquified natural gas in certain
applications. By a combination of strategies, increased peak pressure, insulation
of combustion chambers, recovery of waste heat, and friction reduction, thermal
efficiencies of 55% might be achievable, though there are unresolved questions
about nitrogen oxide emissions (US DOE/OHT, 1996). For medium-heavy trucks used
in short distance operations, hybridization may be an attractive option. Fuel
economy improvements of 60%-75% have been estimated for smaller trucks with
5-7 litre engines (An et al., 1999). With drag coefficients of 0.6 to 0.9, heavy
trucks are much less aerodynamic than light-duty vehicles with typical drag
coefficients of 0.2 to 0.4. Other potential sources of fuel economy improvement
include lower rolling resistance tyres and reduced tare weight. The sum total
of all such improvements has been estimated to have the potential to improve
heavy truck fuel economy by 60% over current levels (Interlaboratory Working
Group, 2000).
3.4.4.10 Systems Approaches to Sustainability
Recognizing the growing levels of external costs produced by the continuing
growth of motorized transport, cities and nations around the world have begun
to develop plans for achieving sustainable transport. A recent report by the
ECMT (1995) presents three policy “strands”, describing a progression
of scenarios intended to lead from the status quo to sustainability. The first
strand represents “best practice” in urban transport policy, combining
land-use management strategies (such as zoning restrictions on low-density development
and parking area controls) with advanced road traffic management strategies,
environmental protection strategies (such as tighter pollutant emissions regulations
and fuel economy standards), and pricing mechanisms (such as motor fuel taxes,
parking charges, and road tolls). Even with these practices, transport-related
CO2 emissions were projected to increase by about one-third in OECD countries
over the next 20 years and by twice that amount over the next 30 to 40 years.
A second strand added significant investment in transit, pedestrian, and bicycle
infrastructure to shape land use along with stricter controls on development,
limits on road construction plus city-wide traffic calming, promotion of clean
fuels and the setting of air quality goals for cities, as well as congestion
pricing for roads and user subsidies for transit. The addition of this strand
was projected to reduce the growth in CO2 emissions from transport to a 20%
increase over the next 20 years. The third strand added steep year-by-year increases
in the price of fuel, full-cost externality pricing for motor vehicles (estimated
at 5% of GDP in OECD countries), and ensuring the use of high-efficiency, low-weight,
low-polluting cars, vans, lorries, and buses in cities. Addition of the third
strand was projected to reduce fuel use by 40% from 1995 to 2015.
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