In 1988, two trains collided in the Bronx after an engineer apparently ran through a red stop signal.

WSJ: Train Derailment Injures Dozens

Engineers used plastic dams in a bid to stop water getting into signal boxes at Cowley Bridge, Devon.

BBC: South West rail problems could last five days

Obama also made clear that Israel has the right to defend itself as it sees fit, which amounted to a diplomatic signal that Washington would not stop a unilateral Israeli strike at some future point if no progress occurred.

CNN: Obama, Netanyahu agree on preventing nuclear-armed Iran

Because tunnels block a radar signal, trains rely largely on hard-wired equipment like the box beside the track, which helps drivers and dispatchers talk to each other and controls a machinelike traffic signal, giving the drivers basic commands to stop and go.

NEWYORKER: Boss Rail

This system, Positive Train Control (PTC), is intended to stop or slow a train automatically if a driver goes too fast or passes a red signal.

ECONOMIST: American railways