Although speeds are typically lower in rail than in road linehaul, air resistance accounts for a significant proportion of the energy usage on freight trains. Examples of aerodynamic measures to reduce these losses include streamlining of train sides and underfloor areas, ordering of freight cars to optimise the aerodynamic profile, minimising gaps between cars or using air bags to fill gaps, covering open top cars or hoppers and using bogie covers. Software is also available to assist with monitoring the frequency and length of gaps between wagons, providing a rating of the overall aerodynamic profile. This can be supplemented with other software modelling to determine the optimum order of containers along the train’s length.
Aerodynamic improvements are greatest when applied along the whole train length. A significant volume of Australia’s bulk commodity freight (grain and minerals) is transported by unit trains which can enable the use of aerodynamic improvements more readily due to consistent wagon design and operation.
Specific improvement opportunities are greatest for intermodal container trains as aerodynamic drag can be as much as 25% higher than unit trains. This suggests there is a real opportunity for use of optimisation software.
There is, however, a significant gap in availability, as no rolling stock providers were identified who could provide examples of fuel savings achieved through wagon redesign.
The most substantial wagon redesign for aerodynamic improvement would require complete replacement. However, changes to inter-wagon gaps could be provided as a shorter term alternative, albeit with a lower level of fuel savings.
Optimisation of wagon assignment using software can deliver reasonable savings in specific cases. A US modelling comparison between optimal and worst case scenarios indicated potential fuel savings of up to 2.2 L/km per train. Analysis of a major intermodal route revealed the potential to reduce fuel consumption by 56 ML per year with a corresponding saving of US$28m.
Bogie and wheel covers have also been identified as a significant source of aerodynamic drag. Studies have shown that a reduction in drag by 10% has equated to a fuel saving of 6–7%.
Key implementation considerations
Most wagon redesign and wagon assignment is based on increased load capacity (weight). As such, few aerodynamic initiatives are adopted due to higher costs compared to fuel savings and operational restrictions from interference with loading and unloading. Some aerodynamic improvements could also be vulnerable to damage, and would increase loading times (particularly changes to wagon assignment). Feedback from industry consultation suggests that higher fuel prices may prompt a re-examination of aerodynamics as a cost-saving opportunity.
Examples of implementation
Vortex optimisation of slotted tops and cavities of two different open-rail wagons
This RMIT study does not provide recent information of technology innovations to improve aerodynamics. However, it does provide useful technical information on the aerodynamic drag of open-rail wagons in Australia. In this study, fuel usage was expected to reduce by 4–6% as a consequence of Vortex optimisation of slotted tops and cavities of two different open-rail wagons in Australia (Saunders et al. 2003).
Optimizing the aerodynamic efficiency of intermodal freight trains, 2005
This academic paper (opens in a new window, PDF 680 KB) highlights the research outcomes of using a wayside machine vision system to monitor the slot efficiency of intermodal trains. The study recognises the physical constraints imposed by the combination of loads and the railcar design that intermodal train operators face and demonstrates the use of advanced image processing technology to assist in improving the aerodynamics of train configuration (Yung-Cheng Lai et al. 2007).
For the full report on fuel saving opportunities in the road and rail sectors, see Fuel for Thought – Identifying potential energy efficiency opportunities in the Australian road and rail sectors (opens in a new window) PDF 1.5 MB.