Whereas radio controlled train operation has reached the stage of pilot projects, so far no realisation of moving block based on radio transmission is known.

• Seltrac by Alcatel, an early and reduced version of moving block, has reached the application stage.
• The ETCS level 3 is confronted with some problems of technological and operational nature still to be resolved. After Railtrack retreated from equipping its West Coast Main Line with ETCS Level 3, there are presently no plans for introducing this level on any line in short term perspective. The new German high speed line Cologne – Frankfurt, opened in late 2002 for 300 km/h, could be appropriate to test ETCS service, since it will be limited to modern high speed trains. There is a number of European lines where all ETCS levels will be tested in the next years (on of them being the DB line Ludwigsfelde - Jüterbog).
• Pilot projects for an ETCS-analogue radio control on regional lines are under way in Germany and France. While theoretically allowing moving block as an option, these lines will be operated in the near future by a radio controlled fixed-block.

• Improvements in operations and in operating capacity (motivation for moving block)
• Reduction of fixed infrastructure costs, since expensive wayside equipment is replaced by on-board devices (motivation for communication based train control not necessarily implies moving block)

Increased capacity

• The development should lead to more regular traffic flows with fewer delays. Exploitation of Moving Block capabilities will permit railway administrations and operators to increase line capacity, utilise the network infrastructure more efficiently, and improve service.
• The improvement in capacity will provide opportunities for independent operators to use the common infrastructures.

Transition costs

The transition from track-side signalling to GSM-R based “virtual” signalling is confronted by a number of specific problems of economic and organisational nature:

• Longevity of systems: Typical depreciation periods of train control systems are about 20 years. It is therefore not economical to abandon the system earlier. This issue is particularly relevant if national authorities are involved in financing infrastructure measures (as is the case in Germany).
• Cost distribution: Even though the technical transition from track-side signalling to GSM-R based “virtual” signalling is expected to prove economical from an overall perspective, the track-side savings have to be paid by additional investments for vehicle equipment. Consequently acceptance problems arise if infrastructure and vehicles are managed by different companies. This issue is virulent even within the DB AG, where the infrastructure operator DB Netz profits from the transition whereas DB Cargo and DB Reise are confronted with additional costs.
• Apart from these intrinsic problems of the technological transition, the international character of the ETCS process brings about lengthy decision making and standardisation processes.

Technological shortcomings

ETCS level 3 poses a number of technical challenges to be resolved:

• To the present day there exists no satisfying solution for the on-board train integrity check of freight trains. The US principle of „end of train telemetry“ with a radio device on the last coach is rejected by European operators due to difficult logistics.
• There remain uncertainties concerning the ways for securing switch sections. In a fixed block system this is done by the signalling stations, in a ETCS 3 system the train distance is to be controlled by the Radio block centres. Their operating logics is to be clarified as far as switch areas are concerned.
• Security standards pose very high requirements on the preciseness and infallibility of train positioning. Although this challenge seems to be resolved in a satisfying manner by a combination of EUROBALISES, radar and odometers, the system still awaits the official operating permission by the railway institutions (respective tests for operation permits by the German EBA (Eisenbahnbundesamt) will be finished by 2003).

Uncertainties about effect on traffic fluidity

The performance benefits of moving block as compared to fixed block operation is questioned by some authors. They hold that contrary to what is generally believed the difference in track performance of fixed block with shortened block lengths as compared to moving block operation is negligible because the performance of a given track today is much more influenced by timetable structure than by distance control.

• As far as capacity and smooth traffic flow are concerned, moving block is most effective if the train speeds on a given track are homogeneous. A principal success factor for moving block is therefore the strategy of network separation.
• Energy efficiency is not a key driver for the introduction of moving block. Nevertheless, more reliable information on the efficiency potential of moving vs. fixed block train control is needed and could supply additional arguments for radio-controlled train operation.