October 27, 2017
"Getting There" - The Myth of the Third Rail
Hardly a season goes by without service on Metro-North being disrupted by a “wires down” accident. That’s when the overhead catenary that powers our trains breaks or is ripped from its poles, cutting electricity and service and ruining the commute for thousands.
But why do we rely on such fragile wires, some of them installed 100 years ago? Isn’t there a better way of powering our trains? Probably not.
Consider this: ours is the only commuter railroad in the US that relies on three modes of power: AC, DC and diesel.
Trains leaving Grand Central first operate on 750 DC current picked up from the third-rail, just like NYC’s subways. Around Pelham, in Westchester County, the trains raise their pantographs (those triangular shaped contraptions atop the cars) and convert to 12,500 volt AC current picked up from the catenary, hence the phrase “operating under the wire”.
On the Danbury and Waterbury branch lines there is no electricity, so those trains must be powered by diesel. But even those diesels must operate on third-rail power in the Park Avenue tunnels for environmental and safety reasons.
That’s a lot of technology for one railroad to administer, and a lot of electronics. That is why the M8 cars that operate on AC and DC require separate power processing, adding to their cost. The third-rail only M7 cars that run on the Hudson and Harlem lines cost about $2 million each. But our newer and more complicated M8’s cost about $2.75 million apiece.
So a lot of people ask me… “Why not just use one power source by converting the entire line to third rail?” As with so many other seemingly simple solutions there are several good reasons why it wouldn’t work.
Mind you, the idea was studied by CDOT in the 1980s and rejected. And here’s why:
1) There’s not enough room to add a third rail along most of the four-track system. You’d have to move the tracks, widen the right-of-way and expand a lot of the bridges and tunnels it uses. Imagine the cost.
2) Even if we did convert to third-rail, we’d still have to maintain the overhead catenary system for Amtrak whose locomotives get their power under the wire.
3) A third-rail power system needs more real estate: power substations every few miles, adding to construction and cost.
4) Third-rail DC power is nowhere near as efficient as overhead wire AC power. That means slower acceleration in third-rail territory and speed limits of about 75 mph vs 90 mph under the wire. Remember… the fastest trains in the world (like the TGV and Shinkansen) operate under the wire, though theirs is not as aged and brittle as ours.
5) Third-rail is dangerous to track workers and trespassers. Overhead wires, much less so.
6) Third-rail can ice up and get buried in blizzards, causing short-circuits. We’ve had some amazing winter weather in Connecticut, but nothing that piled snow high enough to touch the overhead wires.
I’ll admit that weather does cause problems for the catenary. In extreme heat it can expand and sag and in bitter cold it can become brittle and snap. Both conditions require our trains to operate (even) more slowly, but they still get you where you’re going.
So what’s the solution to our “wires down” problems? Accelerated replacement of old wire, better maintenance of pantographs and a little common sense… and not conversion to third-rail.
Reposted with permission of Hearst CT Media