The Metropolitan Transportation Authority had declared the ATO “ready to go” as early as fall 2006, but L trains have been operating in ATP-Manual mode (similar to cab signals) since January of that year on segments of the line where CBTC had been cut in. Motormen remain on board to initiate train starts. They respond to an alerter that starts beeping after 20 seconds; if the signal is not acknowledged, the train goes into penalty braking after 10 seconds. The alerter feature, which replaces the traditional "deadman's" function, had been a sticking point between NYCT and the Transport Worker's Union. NYCT had also initially wanted to operate trains with one person (motorman only, no conductor), but the TWU fought against that also, arguing that both practices would be unsafe. Canarsie Line trains continue to operate with two-person crews, whether in ATP-Manual or ATO.
MTA hopes the $326 million project will allow tighter headways and increased train frequency. The L line was chosen in part due to its relative operational isolation as a self-contained subway line, making installation and testing procedures easier to monitor and evaluate.
MTA New York City Transit and its prime consultant, Parsons-led ATSG (Advanced Technology Signals Group), devised an innovative method of securing interoperability. It involved awarding a "Leader" contract and one or more "Follower" contracts, the intent of which is to have Followers ensure that their systems are interoperable with that of the Leader.