The development of freight rail must have as its starting point optimised freight transportation on the basis of a system view of the railways: from the customer’s transportation needs that put demands on the wagons – the wagons are coupled together into trains where available tractive power is taken into account – the train utilises the infrastructure with a certain performance along a link and ultimately in a network from origin to destination.
In SP3 simulations and models to evaluate enhanced capacity has been investigated. The aim of this report is to analyse the possibilities to increase capacity for future freight trains 2030/2050. The capacity will be described in terms of
- Line capacity – the infrastructure described in
- The track system
- The signalling system
- The train capacity – described in
- The locomotives and the tractive effort
- The wagon performance
Capacity has then been evaluated for some scenarios and combinations of infrastructure and train performance and with examples of parameters from a rail freight corridor.
The capacity of a single-track is highly dependent on the distance between the crossing stations and the trains’ speed. The shorter the distance between the crossing stations, the higher the capacity and faster trains means also higher capacity because they can reach the crossing stations faster.
On a double-track line, the mix of trains operating at different speeds is of great importance as regards capacity. If slow trains, such as freight trains or regional trains, are mixed with express trains, capacity falls because the trains cannot overtake randomly. The trains can be slow because they stop at many stations (regional trains) or because they have a lower top speed (freight trains).
In practice, capacity for different track systems will be in the order of:
- 2 trains/h single track with crossing stations every 20 km
- 4 trains/h single track with crossing stations every 10 km
- 10 trains/h double track with heterogeneous traffic
- 15 trains/h High Speed Rail with stops and passing trains
- 20 trains/h Double track with homogenous speed
- 30 trains/h Metro or commuter trains with ideal operation
- 40=20+20 trains/h four track or double track + high speed line
Capacity can never be greater than the weakest link. Stations or nodes are often dimensioning factors when trains are to stop or brake to change tracks. The capacity will fall if there are many delays or disruptions in the operation.
The signalling system is also important for capacity, especially on double track. The block lengths and the speed and acceleration and braking performance are important. In general, shorter block lengths will increase the capacity. Introduction of the European signalling system ERTMS level 2 can increase the capacity substantially only if the block lengths are shortened and optimized, se figure 2. The best solution is ERTMS level 3 with continuous blocks but this is not on the market yet.
The capacity of the trains can be improved by:
- Higher tractive effort
- Higher axle load and adhesive weight
- Higher axle load and meter load
- Extended gauge
- Better length utilization
- Lighter wagons
- Higher speed
- Better braking systems
- Longer trains and a combination of infrastructure and train performance
Heavier trains can be operated if the fully potential of modern locomotives will be used with higher axle load and thereby adhesive weight. Many locomotives are optimized for fast passenger trains with low axle load. With track friendly bogies it will be possible to have the same axle load on the locomotives as for the wagons, 22.5 tonnes.
Faster freight trains can increase capacity on day-time to get more slots between faster passenger trains and minimize overtaking. Even if faster trains are more costly the total cost can be lower with increased productivity when it is possible to get one more turn of a trainset or locomotive per day.
Some calculations for different infrastructure and train scenarios for 2030/2050 for different train types are shown in figure 3. Train load has the biggest potential to increase capacity if infrastructure and trains can be adapted to the actual needs from the market. Wagon load also have a big potential but need implementation of an automatic couple if it shall develop instead of decrease. Inter modal trains have also a potential especially with longer trains but is restricted by the size of containers and trailers and also by the transferring costs at terminals.
Longer trains are one of the most promising measures which can improve capacity rather much. In combination with improved locomotives, wagons and heavier trains the train capacity can be doubled. The line capacity will increase a little bit less because a longer train will block the line longer time, even with short block sections.
Infrastructure investments as double track and new High Speed Lines are very costly and take long time to realize. Improvement of train performance as heavier and longer trains, maybe in combination with higher axle load and extended gauge, seems to have a big potential if we really will improve capacity for freight in a medium term perspective.
Higher axle load in combination with extended gauge adapted to the actual needs on the market can improve capacity in the order of 10-20%, wagon improvements in the same order. Longer trains have the biggest potential a full step from 630 to 1050m will improve the line capacity with approximately 50%. ERTMS L-2 can improve capacity with approximately 40% with optimized block sections, more with continuous blocks as in ERTMS L-3. Because it is costly to shorten block lengths when introducing L-2 it is important to develop and introduce L-3 on the market.
By combining these measures it is possible to double the freight transport capacity on given line or freight transport corridor if needed.
Stockholm: KTH Royal Institute of Technology, 2017. , p. 75