>Delays involving single tracking

>

Like thousands of other Metrorail riders, I was affected by both track equipment derailment incidents last Thursday, which caused single tracking of the Orange line in the morning rush hour periods as well as the evening rush hour.  This caused my normal 40 minute train ride home from Eastern Market to West Falls Church to be about an hour and a half.  I’ve requested the incident reports and other records and hope to be able to take a look at them, write up a good article and distribute them soon.

When I was stuck on the way home, I noticed something odd about the way Metro was dispatching trains.  Metro was single tracking trains from East Falls Church to West Falls Church, but the backups were all the way back to Rosslyn and beyond.  It appeared that every train that was entering the Orange line at Rosslyn was being sent all the way through the single track area to Vienna and back again.  For a long segment like East Falls Church to West Falls Church, travel time including clearing switches at both ends could be 10 minutes or longer.  This limits the line capacity to one train every 20 minutes in each direction.

The problem is, with a single tracking segment so far from the center of the city, if Metro sends every train through the single track section, it effectively off the capacity of the entire line.  If Metro can only send one train through the single track area every 20 minutes, then it can only send one (Orange Line) train every 20 minutes through Metro Center, and only one every 20 minutes can leave New Carrollton. 

What if instead Metro had decided to turn every other train around at Ballston?  The line before Ballston would travel twice as fast, with a train now able to go every 10 minutes.  Some people would have to get off somewhere before Ballston to change to a through train, but everyone getting off at Ballston or earlier would have a shorter ride.  There are probably few passengers riding from Vienna to Dunn Loring, so it would make less sense for Metro to turn trains around there to go back to Vienna.

The situation improves a bit more if more trains are turned around, but it’s possible that platform capacity at Ballston would be overwhelmed by completely offloading two out of every three trains there.

Based on my discussions with system planners, I know Metro tries to maintain a “one seat ride” for passengers so transfers are minimized.  However, I think in this case the passengers would be happy that their seat is traveling twice as fast, even if they might have to wait 10 minutes to transfer if they’re going further than Ballston.

I’ve asked WMATA about this issue and hope they will get back to me soon with something I missed when I thought about it.

Advertisements

About perkinsms

I'm an engineer and father interested in transit, parking and economics.
This entry was posted in transit, WMATA. Bookmark the permalink.

2 Responses to >Delays involving single tracking

  1. Scott says:

    >Sometimes Orange Line trains end at West Falls Church, which has three tracks within the station. During track work between Vienna and Dunn Loring, for example. My understanding is Metro can’t turn around trains at Ballston (or most stations) because the tracks don’t allow it in a reasonable amount of time.

  2. Michael says:

    >According to the track map I have, there’s a crossover just short of Ballston in the outbound direction. It may not be the preferable mode of service to turn around trains at Ballston, but it seems that rather than single track the whole way and have 20-minute headways, WMATA should pull a train into the “A” platform, offload the train, have a 2nd operator on the platform ready to take over at the other end, and pull the train out the station across the crossover to the “B” track, inbound. The operation should take less than the 10 minute headway expected. I can provide the track map if you email me.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s