Tuesday, July 14, 2015

The Silver Line is Open: What About Performance?

Correction: The Rail On-Time Performance chart has been updated with one that includes the Blue Line. I apologize to all BL riders that I left off. Thanks to @keck41 for alerting me.

With the WMATA Metrorail Silver Line Phase I now open, the overall system appears to still be functioning but is hobbling along more now than ever. In customers eyes delays have increased, breakdowns and single-tracking are more frequent, and crowding has grown. The recent WMATA proposal to optimize the rail system calls for cutting trains on the Orange, Silver, Yellow, and Green lines while Blue line service capacity would be increased. In order to attempt to optimize trains running through the Rosslyn tunnels - each with a theoretical maximum of 26 trains per hour - WMATA wants to reduce the total number of trains running through from 26 to around 23 trains per hour, and increase the percentage of 8-car trains being run on the lines. One of WMATA's lines of reasoning for this change is train spacing:
“All those trains really have to hit that tunnel almost perfectly timed. If one thing goes off, it can throw off the entire system,” said [Sherry] Ly. Running fewer trains would improve reliability, she said. The proportion of eight-car trains on the affected lines also would increase (most rush hour trains currently carry only six railcars).
Is this the proper question that needs to be solved, however, and really why Metro is making this change? The ultimate reason, more likely, is that Metro badly needs to reduce the number of train cars in service in order to increase performance again. Here's why:

Rail Line Performance

WMATA Rail Line On-Time Performance, 2009-2015
To get an idea of the overall picture, this graph shows the WMATA on-time performance for all rail lines dating back to mid-2009. Visible starting July 2014 is the addition of the Silver line with an average on-time performance through March of 86.5% - the lowest average on-time performance of all 6 rail lines between opening July 2014 and March 2015.The introduction of this new line correlates incredibly well with significant decreases in performance of the Orange and Green lines, and less so for the Red and Yellow lines. For the most part through the entire chart, all lines are reasonably close in performance numbers relative to each other.

Rail Equipment

To take a look at another part of the equation, have you ever wondered about the reliability of the rail cars that Metro runs? Not all of them have the best history. While they are the oldest, the 1000 series actually does not have the worst mean distance between delay (MDBD) measurement (granted, they have other critical issues). At an average distance of 30,788mi, the 4000-series cars are the least reliable in the WMATA fleet*. This is only all too clear on the graph below. The second worst-performing series in the fleet are the 1000s, closely followed by the 5000s at 50,028 an 51,456mi respectively. Given the data available, there does not appear to be a statistically-significant correlation between the Silver line opening and rail car performance itself. There is potentially a decrease in performance of the 6000-series cars after the Silver line opening, but there isn't enough data yet to know if that's a temporarily blip or a new long-term trend.
WMATA Rail Car Mean Distance Between Delays (by Series) - 2009 - 2015

WMATA Rail Car Series Mean Distance Between Delays, Oct/2013-Mar/2015

Rail Line Impact

Available from WMATA is the Daily Service Report (DSR), which tracks all customer delays of over 3 minutes. The data pulled out in the graph below are the trains that were canceled or otherwise did not operate in the Metrorail system for the Orange and Silver lines, known as those that Did Not Operate (DNO). A train might be marked as DNO for a variety of reasons, but one main cause can be attributed to not having enough cars to make a full train. For instance, if there are too few or an odd number of cars available to make a train consist, that train is not able to run. One other way to get a DNO train is if WMATA only has 1000-series cars and no others to act as the head and rear of the train; thus, the train would not be able to run.
Number of Non-Operating Trains per Month, August 2013-July 2015
Monthly train cancellation data, August 2013-July 2015

Up until June 2014, the graph shows a nice even distribution of DNO on the Orange line, hovering between around 7 per month. This all changes when the Silver line becomes operational, however. At that point (July 2014), the numbers appear to spike fairly dramatically. Vienna station hits a maximum of 50 DNO trains in the month of June 2015, and there are several months of over 20 trains that did not operate as scheduled from Vienna. Impacts on New Carrollton are visible as well, but not nearly as severe, likely due to station location and yard storage. The average number of DNO trains on the Orange line increases from 7 per month on average before the Silver line opened to 13 per month, and 23 per month when combined with the Silver line's numbers after its opening.

What do these numbers mean? They're pretty abstract and don't necessarily mean anything by themselves.

Lets, for example, take a look at February 2015, where 30 trains originating at Vienna were marked DNO. Given current operating rates, we can estimate ~33% of these DNO trains should have been 8-car, and the rest should have been 6-car trains. Per WMATA documentation, an acceptable capacity of each rail car is approximately 100 people. These 30 trains that did not operate account for 200 total rail cars, which could hold approximately 20,000 riders. These 20,000 riders them must crowd onto other trains, thus increasing the crowdedness of each of those. Overly-crowded trains then exacerbate platform overflows when train offloads inevitably happen, and so on.


Not enough train cars
There are a multitude of reasons why performance on the rail system is suffering, but there are only a couple of conclusions that can be drawn from this subset being discussed. One, WMATA does not currently have enough train cars to run the full system including the Silver line. The Silver line (phase I) requires 64 train cars to operate. These 64 were to have been supplemented by the 7000-series cars, of which only 16 are currently in revenue operation due to various delays. WMATA dictates that the current system requires 954 train cars to operate and the agency has approximately 1126. Approximately 25% of the total cars in WMATA's possession are designated as being out of service for maintenance, spare, or other reasons. With 954 cars required, this drops the operating spare ratio to only 15% and sometimes even lower.

With fewer cars available to put into service when others break, it is more likely to see domino effects. 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), In addition, each car is likely to have less available time for maintenance meaning the chance of breakdown increases over time.

Train cars do not meet reliability targets
For years, WMATA has targeted a reliability level of 60,000 track miles between delay. Of the series measured, only the 2000/3000 and 6000-series cars have managed to average above the target over time. Lower train car reliability is hurting performance and increasing problems/offloads. This will hopefully change as the 7000-series cars enter service, but it is far too early to be able to know that for sure. Each offload has a ripple effect through the system and can cause significant customer delays, so it is imperative for WMATA to increase car reliability and keep it as high as possible.

What WMATA is Doing

By cutting service on Orange/Silver/Yellow/Green, WMATA is doing two things: a) allowing train schedules to synchronize to make running the system easier, and b) reducing the number of train cars needed to run service.

Greater Greater Washington goes into great detail about the train spacing and its effect on the system, so I won't touch on that here. The reduction in cars needed will mean that more cars have more time for routine maintenance and light repair. If WMATA takes care of their cars, it may even be possible to increase the reliability of the rolling stock thus decreasing brake issues, door problems, and ultimately offloads. If the reduction in service is approved, that is one outcome to look forward to. Meanwhile, expedited delivery and testing of the 7000-series cars is necessary in order to properly run the Silver line and the Metrorail system with the cars necessary.

While these actions do not make up for the larger issues plaguing the system, it is one possible way to return a tiny bit of normalcy in the currently-troubled history of the system. This action could be the right thing to do, however the road back to a happy and healthy transportation system is going to be long and tumultuous.

* Data used for this measurement is monthly performance data from July 2008 to March 2015.