Summarises the limits for compatibility between future interoperable rolling stock and track circuits. The gabarits for different traction systems available in Europe are defined up to and including the highest frequency range occupied by existing track circuits but the limits in the gabarits are not the existing limits used for acceptance on a national basis. The proposed limits are still under consideration by Working Group WGA4-2 of CENELEC and therefore the data presented should be used for information only. The basic characteristics of future interoperable track circuits will be developed concurrently.