Leading the way on an up-and-down journey around the girders, steel walkways and angled planks of the underbelly of the railroad bridge over the Norwalk River, state Department of Transportation Assistant Rail Director John Bernick pointed out the 118-year-old span's age-related problems.
A massive set of oil-blackened gears near the center of the bridge are central to the mechanism that rotates the span out of the way when boats need to get by, he said during a Wednesday tour of the bridge.
"It does everything," Bernick said, an early summer breeze blowing by as the river slid past below.
The gears set in motion all of the things that have to happen to allow the bridge to move out of the way to allow boats through, and to close again to let trains cross the river. They were the cause of the two most recent mechanical failures that left the bridge stuck open for hours at a time, preventing all trains from getting past.
Unlike other moveable bridges that rise vertically or from one side, the Norwalk River rail bridge is a swing bridge, meaning it rotates on a central pivot, almost like a record on a turntable. For that to happen, the gears have to move the wedge-shaped steel blocks that lock the bridge into its closed position, the connector tracks between the rail on the bridge and the rails on the approaches to the bridge must lift up, and the catenary on the bridge must disconnect from that of the main tracks on either side of the bridge.
The gear mechanism is what gets all of that going.
" Driving the wedges dictates the size of these gears, lifts the rails, and lifts the connections to the catenary on top," Bernick said.
In both cases, the same gear broke, Bernick said. In the first instance on May 29, the gear jammed into a floorboard, which had to be cut away to allow the gear to move again. The second time, on June 10, that gear fell off completely, he said.
When the gears themselves work, other things can go wrong. The wedge-shaped steel blocks at either end of the span sometimes don't fit back together again properly after opening.
"It drifts slightly on the center bearing when it opens and closes, and doesn't line up exactly where it did in 1895," Bernick said.
The DOT came up with a short term fix for that problem by installing centering pins that yank the blocks back into alignment.
Whatever the cause, it takes hours to fix the bridge when it gets stuck. The jammed gear on May 29 took six hours to fix.
"We've had a history of failures, but not a history of six-hour failures," DOT spokesman Kevin Nursick said. "With moveable bridges, even the new ones fail, but you don't want six-hour outages."
The bridge failed 16 times in 2013, often on hotter summer days when the metal expands and prevents parts from reseating again. It opened 271 times last year. Read Full Article
Given that failure rate, the railroad places about 30 workers on posts around the bridge to monitor all of its moving parts when it opens.
In addition to halting commuters up and down the New Haven Line when the bridge gets stuck, it also brings Amtrak's northeast corridor to a halt because that one bridge carries all four rail lines. There are other 100-year-old moveable rail bridges on the line that also get stuck, but those bridges have two spans, with only two rail lines on each, so if one bridge gets stuck, the other can still carry rail traffic.
That most recent failure of the Norwalk River rail bridge spurred Gov. Dannel P. Malloy to convene an emergency crisis summit with Metro-North Railroad officials to demand short-term solutions.
The bridge is expected to be replaced, but funding for that is uncertain, and, even if the money were lined up, it would take several years before actual construction could start. The state applied for nearly $350 million of federal funds this spring.
So while the ultimate goal is to get the bridge replaced or totally rebuilt so it can open without getting stuck or requiring 30 workers to be on hand it case it does, the current drive is to identify a short-term action plan, Bernick said.
Ironically, between the daily breakages and the planning for a series of interim fixes to improve reliability of the bridge until it can be replaced, routine maintenance takes a back seat.
A November mechanical report commissioned by the state from bridge engineering consultant Hardesty & Hanover outlined more than 20 repairs that were recommended to be done within two to six months.
Metro-North was unable to say definitively which of these had been done or even started, characterizing them as unrelated to the bridge getting stuck or to improving its reliability. The recommended repairs included replacing missing and twisted spokes in the pivoting mechanism that rotates the bridge, missing bolts on lifting rail joints, and wear and tear on gears.
Nursick said engineers prioritize repairs based on an engineering analyses made during inspections, and that anything deemed an immediate priority would have been completed.
"If you think about the analogy of a car it applies. If you check your tire treads and they are down to 40 percent you keep an eye on it, but if your brakes are down to 10 percent you get them addressed immediately.
"If there is a ding in your windshield you pay attention to it and hope it doesn't spread. We handle the critical repairs first."
Asked to review the report, University of Delaware College of Engineering railroad engineering professor Allen Zarembski, said the noted flaws did not seem to reflect a situation where the bridge could not be operated safely. But he did say it would take a lot to keep it functioning.
"The bridge condition does not appear to be critical or in immediate danger of catastrophic failure," Zarembski said.
"It sounds like there is significant maintenance work that needs to be performed over the next 6 to 12 months."