A year after a spate of heat-related service breakdowns, Metro-North officials have added speed restrictions for the New Haven Line, including a maximum of 50 mph between South Norwalk and the Devon section of Milford during periods of extremely high temperatures.

The restrictions were spurred by an incident last July 22 that stalled three trains, including an early afternoon run that had 200 passengers stuck on board near Greens Farms in Westport for more than an hour in 100-plus degrees when the pantograph arm atop the train became entangled in century-old catenary wire that drooped in the heat, Metro-North spokeswoman Marjorie Anders said.

Under the new guideline, during periods of more than 100-degree heat, trains must have a top speed of no more than 40 mph on various curves between Westport and Stratford, a 50-mph top speed limit on the line between South Norwalk and Devon, and 70 mph on the rest of the system.

The new speed restrictions have been used once this summer, between noon and 10 p.m. June 21, Anders said.

The restrictions also help lessen the risk of breakdowns and equipment damage caused by rails that warp in the heat, Anders said.

"The slow speeds is to protect the trains from running into slack wire under old catenary and in the event there are heat kinks in the rails," Anders said.

While the July 22 service problems helped prompt a successful effort by state Sen. Toni Boucher, of Wilton, and commuter advocates to get a customer bill of rights approved by Metro-North, it also focused attention on improving the reliability of the New Haven Line's equipment and customer service, elected officials and others said.

"I think if there are ways to move the catenary replacement forward more quickly, we should do that," said state Sen. Bob Duff, D-Norwalk, vice chairman of the General Assembly's Transportation Committee. "There are places where there are two tracks out due to the catenary replacement and it's not helpful to commuters from the standpoint of speed." Boucher, a ranking minority member on the transportation committee, said last summer's service problem spurred a focus on customer service and the shortcomings of Metro-North's catenary system -- which is currently being replaced -- and moveable rail bridges, which are to be replaced or revamped later this decade.

"I think the state sees that there can be very negative outcomes from the lack of investment," Boucher said. "Can you imagine if someone had really gotten hurt and had a heart attack, the types of lawsuits the state would have to entertain? I think those risks make investments and improvements mandatory and financially imperative." The Connecticut Department of Transportation reorganized the schedule for the catenary replacement project so the work will be completed by 2017 or sooner instead of the projected completion date of 2021, Connecticut DOT spokesman Judd Everhart said.

The new "constant tension" system is expected to be less vulnerable to malfunctions caused by misalignment of the hydraulic arm on railcars and the power line above the tracks in hot and cold temperatures, according to the project plans.

The shorter time frame was accomplished by delaying the start of work to revamp two of the railroad's century-plus-old moveable bridges, the four-track Walk bridge in Norwalk, and the Saga bridge in Westport from 2014 to 2017, according to Everhart.

A seven-mile stretch of catenary wire between Bridgeport and the Southport section of Fairfield within the corridor of last year's breakdown should be replaced by late 2013, according to the DOT.

Everhart said the changed schedule was not directly influenced by the incident near Greens Farms, though the outage prompted greater focus on customer service and improving reliability.

To limit the likelihood of damage to remaining older sections of the New Haven Line's catenary system, the railroad has established restrictions when temperatures reach higher than 80 degrees.

The railroad's two other lines, which have modern power systems, only observe speed restrictions when temperatures break 95 degrees.

This summer, the railroad has also closed the system's five moveable bridges to river traffic to avoid situations in which the bridges fail to close in hot weather.