Signaling on the Elizabeth Line was something of a challenge. Sharing infrastructure with the Great Eastern and Great Western Main Lines meant also adopting their TPWS/AWS signaling. Preparing for the future, the rolling stack had to be compatible with ETCS, which is currently in use on the Heathrow branch. Within the central core and Abbey Wood branch CBTC was chosen, allowing the Elizabeth Line to reach 24 trains per hour. These stations are also equipped with platform edge doors.