Photo by Adam Fagen on Flickr.

With Silver Line opening soon, Metro is reducing the number of Blue Line trains running between Pentagon and Rosslyn. Reader Daniel W. wants to know why Metro is doing this.

Could GGW offer some insight into why Metro is increasing headway on the Blue Line instead of clearing room in the tunnel by running fewer Orange Line trains but running them with eight cars? WMATA can service the same number of Orange Line riders with one third fewer trains by simply running trains at system capacity.

The current situation is fairly complex. Each Metro line has a capacity of 26 trains per hour (TPH). Right now, the combined Blue/Orange line between Rosslyn and Stadium/Armory is operating at that limit. When the Silver Line starts operating later this month, both the Blue and the Orange lines will see fewer trains to make way for the Silver Line. That much is inevitable.

But the Blue Line reduction is more severe for two primary reasons. First, there’s simply more demand for trains coming from north Arlington, so Metro wants to give the majority of the slots to the Orange and Silver lines. The other reason is that the line coming up from Alexandria and southern Arlington splits at Pentagon. Blue and Yellow line riders have two options for getting into downtown. But for the Orange and Silver lines, the only place they can be routed is via Rosslyn.

Many Blue Line riders are understandably upset about having longer waits for a direct train to the western part of downtown. Now, it may often be faster for riders to take the “rush plus” Yellow Line from Franconia and transfer at L’Enfant. But without a separated subway for the Blue Line, there’s not much WMATA can do to increase capacity.

Comparing capacity

What does the current breakdown look like?


View peak service levels: Pre-Silver Line   With Silver Line
Note: This graphic was originally created in 2013. Since then, Metro has announced there will be 5 TPH per hour on the Blue Line once Silver opens, rather than 6 as shown here.

Right now at Rosslyn during peak hours, there are 19 inbound Orange Line trains and 7 inbound Blue Line trains each hour. That means there’s an inbound train about every 2 and a half minutes.

Of the Orange Line trains, about 40% are 8 cars long and 60% are 6 cars. All of the Blue Line trains are currently 6 car trains. That means that each hour at Rosslyn, there are roughly 42 inbound Blue Line cars and 130 inbound Orange Line cars. This means a total of 172 inbound cars per hour.

Once the Silver Line opens, the distribution will change. Starting on July 28, the mix at Rosslyn will be 11 Orange Line trains each hour, 10 Silver Line trains per hour, and 5 Blue Line trains per hour.

All of the Silver Line trains will be 6 cars in length. The proportion of Orange Line cars is not expected to change, so it will remain about 40% 8-car trains. The Blue Line will operate with half of its trains as 8 car sets.

That means that at Rosslyn, there will be 35 Blue Line cars inbound each hour, a reduction of 7 cars. The Orange Line will also see a reduction, with only 74 cars per hour. The Silver Line will have 60 cars inbound each hour.  Now, since the Silver and Orange share in northern Arlington, riders at stations like Clarendon will see 134 inbound cars each hour, which is a very slight increase. Overall, at Rosslyn, that will mean 169 cars inbound each hour (which is a slight decrease).

So, even though the transit agency is reducing Blue Line frequency in order to fit more trains coming from northern Arlington, the change in the length balance of those trains means that essentially passenger capacity is staying the same. It’s only increasing by 4 cars per hour. And of course, it’s dropping by quite a bit for the stations on the Orange Line west of East Falls Church (from 130 today to 74), though that section of the line is less crowded than the parts closer to the core.

Alternate solutions

Daniel’s question is specifically whether WMATA can have the same capacity by increasing the length of Orange Line trains rather than reducing frequency on the Blue Line.

If WMATA kept the same number of Blue Line trains as there are today — 7 TPH each 6 cars in length — the inbound Blue would have 42 cars per hour. The number of Orange Line trains would still have to change to accommodate the Silver Line, so let’s assume the remaining 19 slots are distributed 10 to the Orange Line, with all 8-car trains, and 9 to the Silver Line, with all 6-car trains.

There would then be 80 inbound Orange Line cars per hour and 64 inbound Silver Line cars per hour, for a total of 144 cars per hour coming through northern Arlington. That would mean a total of 186 cars per hour inbound at Rosslyn, which is significantly more than today.

However, this solution would actually require Metro to use more cars in daily service, and right now, there simply aren’t enough. The Silver Line requires more cars to run, since Wiehle Avenue is so far out. The opening of the new line is already stretching Metro’s fleet. There will be more wiggle room sometime soon, once the first 64 7000-series cars arrive, but that milestone is probably more than a year away.

The other issue is that Metro still needs upgrade power systems on all the lines to enable more 8-car trains to operate. Right now, even if Metro had enough cars, there isn’t enough traction power capacity to run all 8-car trains, though the agency is slowly working to upgrade traction power substations throughout the system.

Metro does anticipate running 100% 8-car trains in the near future. But being able to do so is dependent on being able to finance more 7000 series railcars. Right now, the local jurisdictions — who pay for capital upgrades — haven’t ponied up enough money for that to happen, but there’s still time.

WMATA expects ridership to continue to grow. More people ride the Orange Line in northern Arlington than ride the Blue Line between Pentagon and Rosslyn, and so the transit agency is trying to send enough trains that way. Officials see a Blue Line reduction as the only way right now, and since the Yellow Line bridge offers a relief valve, Metro can still give Blue Line riders just as many inbound trains each day, but some riders who used to have a direct trip may find themselves making a transfer.

The only way to resolve this capacity crunch is, in the short term, for local governments to fund more railcars and more power stations, and eventually build another Potomac crossing. Without a new river crossing, there can’t be more trains on Blue, Orange, and Silver at the same time.

Matt Johnson has lived in the Washington area since 2007. He has a Master’s in Planning from the University of Maryland and a BS in Public Policy from Georgia Tech. He lives in Capitol Hill. He’s a member of the American Institute of Certified Planners, and is an employee of the Montgomery County Department of Transportation. His views are his own and do not represent those of his employer.