Steel has traditionally been used to make freight cars for rail transport. There is potential to make cars out of lighter components such as aluminium, composites or plastics. The weight of rolling stock can also be reduced with improved design and by replacing mechanical control systems with electronic fly-by-wire systems.
This will then enable locomotives to pull more freight without exceeding load limits and to save fuel on empty return runs.
Double-stacking involves placing one high-cube container on top of another. A low-floor wagon is needed so that the double-stack is not more than 6.5m above the top of the rail. Double-stacking can enable trains to carry up to 40% more freight than similar length single-stack trains with no additional power. It also has the potential to reduce traffic on rail networks.
Double-stacking is prevented on some Australian routes as there are lower axle-load limits and smaller loading outlines. Infrastructure investment to support double-stacking enables improved rail efficiency and reduced dependence on road freight.
Driver assistance IT systems, such as portable loggers and GPS receivers, enable freight trains to optimise fuel-efficiency. The onboard computer calculates this based on the type of train, its location, weight, speed, fuel consumption, the gradient and curvature of the track, GPS location and driving techniques. The software provides instructions to optimise power, such as slower acceleration towards maximum permitted speed, coasting and running at lower speeds for gradual deceleration before braking.
New electronic control techniques safely enable freight trains to run closer to each other, allowing more trains to be on the same tracks at one time. The ability to increase the amount of freight carried by rail depends on the number of freight track lines and their length, the amount of load the trains can carry and the speed at which they can be unloaded and reloaded.
Modern switching can be done by moving just the containers across a platform horizontally, rather than shifting entire railway cars for loading.
20 or more containers can simultaneously be switched from one train to another or into a warehouse. An entire goods train can be reconstituted in 15 minutes.
A significant amount of the energy used by freight trains is expended due to air resistance. While studies suggest there is some potential to improve aerodynamics of locomotive engines, there is considerable scope to reduce aerodynamic-drag losses for certain car configurations, such as those that include empty cars and intermodal cars (2 containers stacked on a flat car). Aerodynamic drag losses for intermodal cars can be as high as 30% of the energy used.
This issue can be addressed by various measures, including the use of add-on components that don’t require replacement of rolling stock.
- Streamline the sides and underfloor sections of trains.
- Minimise gaps between cars.
- Fill gaps with air bags and cover open cars.
- Wheel covers to reduce aerodynamic drag.
Software is available to rate the overall aerodynamic profile of a train by examining the frequency and length of gaps between wagons. For best results, the full length of the train must be considered. There is also software that can assess the best sequence of containers for a train.
Trains depend on friction to prevent wheels from slipping or derailing, especially along curving tracks. Wheel/rail friction makes up a significant portion of the energy used in rail transport.
Lubrication to reduce friction levels can also reduce energy use, wear and tear, and excessive noise, as long as it is done in a way that does not compromise wheel-to-rail contact.
Lubricants can consist of oil, grease or water. They can be applied from systems on the side of the track (wayside) or from onboard systems, where the lubricant is mounted on the locomotive or lead car and applied on each curve. While wayside grease is generally more common, onboard lubrication systems are starting to become more widely used.
Electronically controlled pneumatic (ECP) braking involves a communication network that activates the entire train’s braking mechanism simultaneously. The alternative to date has been mechanical systems that operate progressively down the train.
ECP brakes enable trains to operate at higher average speeds and carry heavier loads while remaining within safety limits. Fuel savings can be achieved by improved train handling, reduced wagon braking and lower compressor duty cycles. ECP braking systems also enable the use of longer trains and improved safety.
Optimum benefits are most likely to be achieved where terrain allows faster downhill speeds. This enables the resulting increased inertia to reduce the need for power and maintains higher speeds when travelling up the next hill.
Anti-idling devices use engine management software to shut off the main diesel internal combustion engine and then restart it when certain parameters fall below threshold. Retrofitting devices is not difficult, but fuel savings depend on the length of time spent idling in normal operations.
In Australia, regulations prevent locomotives being switched off on main lines. However, anti-idling devices can be used on private rail freight lines.
Operating at lower speeds and restricting throttle use reduces the need for braking and can also reduce aerodynamic drag.
A number of factors determine both the speed of a train and throttle position, including:
- instructions of the train controllers
- interactions with other trains
- loading and unloading
- Increases in travel time
The US rail company Union Pacific is using speed reduction initiatives as one of its fuel saving strategies. Their ‘Conservation Speed 50 program’ showed there are a number of tasks, which are not as time-critical as others, where average speeds could be reduced.
Alternative drivetrain engine technologies can reduce energy loss and improve overall energy efficiency.
Some examples of opportunities in this area are outlined below.
Replace DC traction with AC traction motors in locomotives
AC traction systems can replace conventional DC traction motors for improved wheel-to-rail traction. This can enable less powerful locomotives, or a smaller number of locomotives, to perform the same task. SCT Logistics used AC Traction to achieve 30% more loading, and was able to replace 4 DC traction locomotives for 2 or 3 locomotives.
Other benefits of AC traction motors include reduced maintenance requirements due to the smaller number of locomotives performing the same tasks and quicker servicing turnaround times.
Investigate hybrid locomotives
Hybrid locomotives operate in a similar way to hybrid motor vehicles. Propulsion power is provided by a large battery that is recharged by a small diesel generator. A regenerative braking system can be integrated into the hybrid combination to convert kinetic energy back into electricity to be stored when braking. The hybrid system also allows the diesel generator to run at a constant speed (the most efficient operating point) and so reduce fuel consumption.
More research is needed to better understand the potential applications of commercial hybrid line-haul freight. Its application could be particularly applicable to long downhill runs or hilly terrain where braking is often used. Many rail lines from mines in Australia run downhill to the coast and could generate net energy output.
It is important to note that there could be rail gauge issues on these new hybrid locomotives which could limit their applicability to Australia.