NEW YORK — After a speeding Metro-North Railroad commuter train barreled into a curve and derailed in New York City on Dec. 1, safety advocates said similar deadly accidents might soon be avoided. Railroads across the country are preparing to deploy high-tech control systems that will let computers automatically slow trains that are moving too fast or headed for a collision.

Yet there is already low-tech equipment, widely available since the Great Depression, that could have prevented the crash, and every Metro-North train already has it.

For many years, the trains have been outfitted with control systems that will sound an alarm if an engineer exceeds a designated speed or blows through a red light, then robotically slam on the brakes if the driver doesn’t respond.

Historically, though, the system has been used on Metro-North mainly to keep trains from colliding, not to enforce speed limits on curves, hills or bridges.

That meant that no alarm sounded when engineer William Rockefeller failed to slow as he approached a tight curve in the Bronx. Federal investigators said the train was moving at 82 mph, well above the curve’s 30-mph speed limit. Four people died in the wreck. Rockefeller said he became dazed or nodded off at the controls, according to federal investigators, his lawyer and a union official.

A week after the derailment, Metro-North adjusted its signaling system so trains approaching the bend too fast will trigger the alarm and automatic braking system.

Similar upgrades are planned over the next few months to enforce speed limits at eight other curves and bridges in Metro-North’s 384-mile system.

The relatively quick fix for the deadly section of track raises a question: Why wasn’t it done sooner?

The simplest answer seems to be that on most U.S. rail systems, engineers have been seen as capable of handling routine speed adjustments on curves and bridges without mechanical backup.

“We operated trains for 30 years and 11 months without a fatality,” said Marjorie Anders, a spokeswoman for the Metropolitan Transportation Authority, which oversees Metro-North operations. She added, though, that since the accident, the agency was rethinking its safety operations from top to bottom. Anders said the MTA hasn’t yet calculated the cost of installing the safety equipment.