A train that derailed in New York City this month had an automatic breaking system that might have prevented the crash, but it wasn't set up to enforce speed limits on the curve where the wreck happened.
Four people died when a Metro-North commuter train failed to slow as it approached a tight curve in the Bronx.
The driver told investigators he nodded at the controls.
Metro-North trains have equipment that will sound an alarm and hit the brakes if an engineer exceeds a designated speed or blows through a red light.
But like many other rail systems, it is configured mainly to keep trains from hitting each other, not regulate speeds on curves, hills or bridges.
The railroad is making changes to allow automatic braking in more locations.
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