6.4.2 Indirect energy savings for weight limited cargo
A weight reduction by 100 kg also allows for a higher payload of 100 kg with the total weight, thus also the energy consumption per vehicle-km, maintained (Tab. 27). An ex- ample from freight transport in the U.S. has been treated by [STODOLSKY et al. 1998]. Diesel locomotives are used and trains are very long with at least three loco- motives and 68 railcars. At an average speed of 35 km/ h freight trains are also very slow. A literature survey of the fuel consumption for freight trains in the U.S. found a range between 0.003 and 0.015 l/ t-km or 107 - 536 kJ/t-km end energy. A typical base- line train with 100 (67.5 t) railcars and nearly 3000 t of load consumes about 0.005 l/ t- km or 178 kJ/ t-km. With a total weight of 7000 t the specific end energy consumption is about 91 kJ/ gross t-km. This end energy consumption is much lower than the value identified for European freight trains, because of the much higher total weight and the more steady and slower speed of the baseline train. The locomotives have a very long life-time of 30-40 years.
Net vehicle weight [t]
Life-time transport performance [t-km]
Tab. 27: Life-time transport performance with different maximum load
Source: IFEU 2002 from various sources
A 100 kg weight reduced freight train can have an up to 800’000 t-km higher life-time transport performance (Tab. 27). This is the equivalent of 267 vehicle-km or 335 GJ of final energy and 386 GJ primary energy during its life-time. For this train, more than four times the direct energy savings (about 83 GJ) can be achieved indirectly. In reality, the indirect energy savings will be lower, because freight trains do not always carry the maximum load. A full load will normally only be achieved outward bound but not during the return trip. On the return trip, however, direct energy savings will be achieved any- way. In reality the share of indirect energy savings determines the increase of energy savings compared to direct energy savings only. If we assume 20 % weight limited transport and 80% volume limited transport our diesel freight train example would achieve 143 GJ and a similar electric freight train about 121 GJ life-time primary energy savings.
Share of vehicle-km
transport 80 %
transport 20 %
Tab. 28: Life-time energy savings of volume and weight limited transport with freight trains
Life-time primary energy savings (Diesel freight train) Life-time primary energy savings (Diesel freight train) Life-time primary energy savings (Electric freight train) Life-time primary energy savings (Electric freight train) Source: IFEU 2002 from various sources