A partnership between Transport for London and BTP led to the formation of the ERU. The unit carries TfL engineers to incidents on the London Underground, such as one unders and terrorist incidents. The vehicles are driven by BTP officers, so once at the scene the officer performs regular policing duties in relation to any crime or public safety issues. The use of the blue lights on the unit's vehicles is subject to the same criteria as with any other police vehicle In December 2013, TfL announced that the trial of blue lights had ended, and that ERU vehicles would retain blue lights, as BTP drivers had halved the unit's response time to incidents. Some vehicles within the unit are dual liveried, allowing TfL engineers to operate the vehicles without a police driver. On these, 'police' branding can be removed and the vehicles returned to the 'emergency' branding utilised prior to the trial, with engineers utilising amber and red lighting as opposed to blue.