The myth of the third rail
Metro-North’s mangled and much-maligned service in Connecticut is made all the more challenging by a technological quirk of fate. Ours is the only commuter railroad in the U.S. that operates on three modes of power ... AC, DC and diesel.
On a typical run from, say, New Haven to Grand Central, the first part of the journey is done “under the wire,” the trains being powered by 13,000 volt AC overhead wires, or catenaries. Around Pelham, in Westchester County, the conversion is made to 660 volt DC third rail power for the rest of the trip into New York. Even diesel trains must convert to third-rail as their smoky exhaust is banned in the Park Avenue tunnels.
And there’s the rub: Connecticut trains need both AC and DC, overhead and third-rail, power pick-ups and processors. That means a lot more electronics, and added cost, for each car. While the DC-only new M7 cars running in Westchester cost about $2 million each, our new dual-mode M8 car designed for Connecticut cost $2.5 million each.
So, some folks are asking ... “Why not just use one power source? Just replace the overhead wires with third-rail and we can buy cheaper cars.” Simple, yes. Smart, no. And here’s why.
• There’s not enough space to lay a third-rail along each of the four sets of tracks in the existing right of way. All four existing tracks would have to be ripped out and the space between them widened. Every bridge and tunnel would have to be widened, platforms moved and land acquired. Cost? Probably hundreds of millions of dollars, years of construction and service disruptions.
• Even with third-rail the CDOT would still be required to provide overhead power lines for Amtrak. That would mean maintaining two power systems at double the cost. We’re currently spending billions just to upgrade the eighty-year old catenary, so why then replace it with third rail?
• Third-rail AC power requires substations every few miles, meaning further construction and real estate. The environmental lawsuits alone would kill this idea.
• DC driven third rail is less efficient. Trains accelerate much faster using overhead AC voltage, the power source used by the fastest trains in the world… the TGV, Shinkansen, etc. On third-rail speeds, are limited to 75 miles an hour vs. 90 mph under the wire. That means, mile for mile, commute time is longer using third rail.
• Third rail ices-up in bad weather and can get buried in snow causing short circuits. Overhead wires have problems sometimes, but they are never buried in a blizzard.
• Third-rail is dangerous to pedestrians and track workers.
The idea of conversion to third-rail was studied in the 1980’s by consultants to CDOT. They concluded that, while cumbersome and costly, the current dual-power system is, in the long run, cheaper and more efficient than installing third-rail. This time, the engineers at CDOT got it right.
Jim Cameron is founder of The Commuter Action Group, and a member of the Darien RTM. The opinions expressed in this column are only his own. You can reach him at CommuterActionGroup@gmail.com. For a full collection of “Talking Transportation” columns, visit talkingtransportation.blogspot.com.