It would be inappropriate to discuss the detail of any current or future counter-terrorist security measures on public transport to avoid potentially compromising their effectiveness.
In its role as the transport industries' security regulator, DfT maintains risk-driven protective security regimes based on assessments of the terrorist threat prepared by the Security Service.
Despite the practical limitations of deploying protective security measures on 'open' mass transit systems, a hierarchy of measures is in place to mitigate the risk of terrorist attack on the UK rail network and London Underground. These are designed to be commensurate with the risk, effective, practicable and sustainable. They are co-ordinated with the work of the British Transport Police.
The situation is kept under constant review to ensure that the measures remain up to date and we continue to look at what further practical measures can be taken to protect transport targets.