If you’ve noticed Metro’s performance declining over the past several months, you’re not alone. In order to open the Silver Line last year, Metro has had to run more train cars longer, and the extra mileage put onto them has meant their breakdowns may affect your service more often.

Graphic by the author.

To get an idea of the overall picture, the graph above shows the WMATA on-time performance for all rail lines since 2011. Silver Line service started in July 2014 and from that point forward you can see a clear 3% decline in on-time performance systemwide (that doesn’t include the big dip on the far right, which is the result of the harsh temperatures of last winter).

The dip in performance relative to before and after the Silver Line opened primarily affected the Blue, Orange, and Green lines. System-wide, on-time performance dropped from 92% to 89%:

Graphic by the author.

Putting more spare trains into service sets the stage

Transit agencies try to keep a spare ratio of around 20-25%. Some cars are going to need to be in the shop for unscheduled repairs, preventative maintenance, or inspections. No transit agency operates 100% of its cars in service at any given time.

When WMATA opened the Silver Line it had not yet deployed the new 7000 series cars needed, so the agency dipped into its spare pool temporarily until enough new cars were set for service.

With a lower spare ratio, Metro doesn’t have enough time to do preventative maintenance or inspections on cars. And when some need maintenance that can’t wait, there may not be enough cars to build a train or the train may break down on the mainline, causing delays.

One impact of the lack of cars is that an increased number of scheduled trains do not operate (DNO). The data shown in the graph below are the number of trains that were canceled or otherwise did not operate on the six lines between August 2012 and July 2015.

Graphic by the author.

A train might be marked as DNO for a variety of reasons, but one main cause can be attributed to not having enough cars available to make a full train. For instance if there are too few cars available to make up a train, that train is not able to run. Alternatively, WMATA might only have 1000 series cars available and no others to act as the head and rear of the train; thus, the train would not be able to run.

Before July 2014, the Orange Line averaged 18 DNO trains per month. When the Silver Line opened in July 2014, that number spiked fairly dramatically. Since then the Orange Line has averaged 45 DNO trains per month, and Vienna station itself hit a maximum of 50 DNO trains in the month of June 2015. The overall system average has increased from 40 DNO trains per month to 141.

When a train doesn’t operate, it creates a gap in service averaging just over six minutes. So instead of waiting, say, six minutes for a train, customers have to wait up to 12 minutes. During that period the platform gets more crowded, and when the next train shows up, it has to carry a larger load.

The more crowded a train is, the longer it dwells in stations, which exacerbates the delay, and can cause bunching. Crowded trains can be more likely to be offloaded themselves as passengers hold the doors trying to get on and off. With the overall system averaging system averaging 7-8 DNO trains per day in June and July 2015, the delays can really start adding up.

So what’s causing the number of DNO trains to spike?

There aren’t enough train cars

There are several reasons why performance on the rail system is suffering, but the main item we can draw from this data is that the railcar spare ratio is too low.

WMATA does not currently have enough train cars to run the full system including the Silver Line. The first phase of the Silver Line requires 64 train cars to operate, which were to have been delivered before its opening. Today, only 32 of these cars are in revenue service.

WMATA says that the current system requires 954 train cars to operate at peak service and the agency has approximately 1,140 available for revenue service use. Metro plans for 24% of the total cars to be out of service for maintenance, spare, or unscheduled reasons, leaving 868 available. But with 954 cars required, that means the operating spare ratio is only 16% and sometimes even lower when more are pressed into service.

With fewer cars available to put into service when others break, we are more likely to see a domino effect of breakdowns. Fewer trains may be available to run at peak hours due to equipment constraints (and thus marked DNO, like when the 4000-series cars were taken out of service earlier this summer). In addition, each car is likely to have less available time for preventative maintenance meaning the chance of breakdown increases over time. To take a look at another part of the equation, the reliability of the railcars that Metro runs varies, the topic of discussion in a recent post.

While the data suggest WMATA doesn’t yet have all the cars they need, help is slowly arriving. The fourth 7000 series train entered service on the Green line this past week, and more are coming, especially once the test/commissioning track near the Greenbelt station is finished. Once at least 64 of the new 7000 series cars are in service, we should start to see a tapering of car-related issues and on-time performance should start to increase again. For all those having to deal with train delays, we hold our baited breath for relief to come.

A modified version of this post ran earlier on Stephen’s website. He tweets online about Metro at @MetroReasons.

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Stephen Repetski is a Virginia native and has lived in the Fairfax area for over 20 years. He has a BS in Applied Networking and Systems Administration from Rochester Institute of Technology and works in Information Technology. Learning about, discussing, and analyzing transit (especially planes and trains) is a hobby he enjoys.