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   Self-propelled freight cars  evaluated  
For smaller quantities of cargo the conventional production system in railways is cost and time-consuming due to train formation and freight handling processes. This problem could be solved by making freight trains more truck-like, i.e. replace long loco-hauled trains by self-propelled freight cars and eventually driverless operation.
Technology field: Increase of load factor and flexible trains
close main section General information
  close sub-section Description

In the freight sector, the specific advantages of rail are ideally exploited by long trains transporting heavy low-value mass goods from point A to point B. The specific advantages of road transport are best realised by small high-value goods that have to be transported in small quantities.

During the last decades, the latter type of freight has constantly increased while mass goods have lost importance. For smaller amounts of cargo the conventional production system in railways has been the one illustrated in solution 1 of Figure 1. This system is cost and time-consuming since the individual units have to be coupled and decoupled in shunting points and often have to wait until enough units have gathered in order to form a long train on the main relation. These problems are one of the reasons why the modal split has changed in favour of road transport.

Figure 1: Customer needs and how they are met by different production systems


Source: IZT (based on Frederich, Lege 1996)

The most obvious solution to this problem is to make freight trains more truck-like, i.e. replace long loco-hauled trains by smaller units with a high degree of modularity and flexibility (due to rapid automatic coupling and decoupling etc.).

These shorter units can be realised in different ways:

  • Short conventional loco-hauled freight trains
  • CargoSprinter consisting of multiple platforms, the end ones of each group are powered by a small diesel motor. The intermediate platforms are unpowered. Several of these trains can be linked together and run in MU (multiple unit) configuration.
  • Individual self propelled freight cars: Each wagon is powered and runs independently (usually requiring driverless operation).

The following refers to self-propelled freight cars since they are the most radical realisation of the concept of modular and flexible freight trains.

Self-propelled freight cars have a propulsion unit on-board. This can be realised by electric or diesel traction, the latter being cheaper and better suited to freight traffic running frequently on non-electrified tracks. Self-propelled freight cars could be used for a direct point-to-point delivery of small freight quantities. From an economic point of view, this can economically only be realised by driverless operation. This requires

  • autonomous navigation
  • automatic avoidance of conflict with other vehicles (replace security control procedure based on fixed railroad sections and visual signalling by telematics applications)
  • new shunting methods due to application of telematics and self-powered waggons


close main section General criteria
  close sub-section Status of development: test series
    There are historical examples for self-propelled freight cars (e.g. the VT 20.5 in the 1930s). In recent times, there have been many steps in this direction, especially the CargoSprinter, a small train unit consisting of two powered and three non-powered cars. At the moment R&D concentrates on the systematic concepts (telematics etc.) behind self-propelled driverless freight cars, such as the SST concept (signal-controlled traction unit) or SOG (self-organised freight transport). Recently there has been a test of the SST concept involving a small loco-hauled train circulating on the railroad track Salzgitter - Wolfsburg (Germany) for freight transport between two Volkswagen plants.
  Time horizon for broad application: in > 10 years
    (no details available)
  Expected technological development: highly dynamic
  • A cost-effective design and layout of self-propelled freight cars is a future challenge for R&D.
  • For the driverless operation of self-propelled freight units there exists no mature system yet. This problem seems principally solvable by future R&D.


  •  Meet the requirements of changing freight markets and win back market share from road transport.
  • Make present production system in rail freight transport more cost-effective.
  Benefits (other than environmental): big

Cost efficiency

No drivers, point-to-point transport, no cost-intensive cargo transport centres freight handling.

Time efficiency

Point-to-point transport, no time-intensive coupling and reloading processes.

Customer service

In the future the customer himself could send self-propelled cars on their way whenever and whereever desired. The goal is to make sending freight for the customer as easy as mailing a letter.

  Barriers: high

Transition costs and system inertia

The introduction of self-propelled and self-organising freight cars would represent a system change in rail-bound freight transport. Not only high transition costs but also uncertainties about the new system constitute high hurdles.

Initial costs

The load-specific initial investment would presumably be higher for powered freight cars than for the loco-hauled production system.


A fleet of self-organising driverless freight cars operating on a mixed infrastructure poses a number of serious safety problems that are currently being studied.

    Success factors:
    (no details available)
  Applicability for railway segments: high
    Type of traction:  not applicable
    Type of transportation:  freight
    (no details available)
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): highly uncertain
    If barriers are overcome, potential for self-propelled freight cars is huge.
    (no details available)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: not applicable
  Energy efficiency potential throughout fleet: not applicable
    It is very difficult to estimate the energy consumption of vehicles and a production system that are only in the concept stage. For aerodynamic reasons, it is however obvious that X self-propelled cars consume more energy than a loco-hauled freight train with X wagons carrying the same freight.

Study by Rauschenberg

There is a theoretical study (Rauschenberg (no year)) examining the external effects of the new system. A very rough assumption is made about running resistance of self-propelled freight cars:

  • rolling resistance is assumed to be equal to conventional freight trains
  • air resistance is assumed to be equal to road trucks

These assumptions, which seem reasonable for a first approach, lead to the running resistance shown in Figure 2. For an average speed of 80 km/h, this yields the comparison given in Table 1. It shows that the running resistance of self-propelled freight cars is roughly 3 times that of a freight car in a loco hauled train

Figure 2: Comparison of running resistance of conventional rail transportation, self-propelled rail vehicles and road transportation


Source: Rauschenberg 2000

Table 1: Comparison of running resistance at 80 km/h for conventional rail transportation, self-propelled rail vehicles and road transportation (figures give load-specific resistance force, i.e. resistance force per unit of weight force of load)

     Road truck    

    conventional freight   

    Self-propelled freight   

Rolling resistance        

1,037 %

0,4306 %

0,4306 %

Air resistance

1,029 %

0,09574 %

1,029 %

Running resistance

2,066 %

0,5263 %

1,459 %

Source: IZT, data from Rauschenberg 2000

Estimate using data from Vollmer 1989

Since a self-propelled freight car will aerodynamically behave similar to the first car in a train the data from Vollmer 1989 can be used to make an estimate on the additional air resistance met by self-propelled freight cars. Since the first car in a train configuration roughly causes 4 - 10 times as much air drag as the following ones, this is also a good estimate for the difference between self-propelled freight cars and loco-hauled stock. This is in reasonable accordance with the factor 10 assumed by Rauschenberg (cf. second line in Table 1)


Assuming that the (load-)specific air drag of self-propelled cars is about 4 - 10 times higher than that of loco-hauled stock, and taking into consideration that air drag accounts for about 50 % of total energy consumption in freight transport, one derives a total energy consumption increased by a factor of 2 to 5.

The additional energy demand will be reduced due to the fact that self-propelled cars travel shorter distances owing to point-to-point service and do not need additional freight handling along the route.

Energy efficiency of self-propelled could be improved by two factors:

  • Running resistance can be substantially reduced by automatic coupling of self-propelled units to form long trains on major routes. This way self-propelled freight cars could exploit the aerodynamic advantages of long freight trains without sharing their drawbacks.
  • The same holds for the concept of Virtually coupled trains with much higher requirements for train formation.
  • If self-propelled freight cars are equipped with electric traction, they can use regenerative braking, which would cut the effect of mass acceleration. This is of course a cost issue, since electric propulsion will be more expensive than diesel propulsion.

The environmental assessment of self-propelled freight cars requires a new perspective. It is hardly reasonable to compare energy efficiency of the new train concept with conventional freight trains since self-propelled freight cars compete for a market segment presently dominated by road trucks rather than rail transport.

Therefore the concept of self-propelled freight cars can be seen as an energy-efficient option even though the comparison with conventional freight trains does not favor them.

Assuming that the system of self-propelled freight cars can be realised which uses automatic train formation on main routes, optimised point-to-point logistics and load management, the overall energy consumption could be comparable or even beat conventional railway freight systems.

  Other environmental impacts: neutral
    (no details available)
close main section Economic criteria
  close sub-section Vehicle - fix costs: high
    (no details available)
  Vehicle - running costs: (no data)
    Driverless self-propelled driverless freight cars save costs for personnel, but increase energy costs. There is no data about the net effect. The main economic benefit of self-propelled freight cars will be to gain a competitive edge in future logistic markets rather than reduce operation costs only.
  Infrastructure - fix costs: medium
    Self-propelled freight cars need less infrastructure for coupling, train formation and reloading etc. but require additional telematics infrastructure.
  Infrastructure - running costs: reduced
    Cost savings due to less infrastructure for freight handling and train formation will outweigh additional costs for running telematic infrastructure.
  Scale effects: medium
    If self-propelled freight cars were ordered in great quantities, there would be appreciable scale effects.
  Amortisation: (no data)
    (no details available)
no data available Application outside railway sector (this technology is railway specific)
close main section Overall rating
  close sub-section Overall potential: interesting
  Time horizon: long-term
    In view of changing demand and freight structure in transport markets, the driverless self-propelled freight car is an interesting concept to win market share for rail-bound freight transport. At present, the concept is too immature to allow a final assessment but it could well become strategically very important for cargo operators in the very long-term perspective. From an energy point of view, the aerodynamic drawbacks of self-propelled units can be partly or completely compensated by an intelligent systemic approach using coupling on main routes as well as advanced logistics.
References / Links:  Bock, Bikker 2000;  Frederich, Lege 1996;  Rauschenberg 2000;  Rauschenberg (no year);  Vollmer 1989
Related projects:
Contact persons:
 date created: 2002-10-09
© UIC - International Union of Railways 2003
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