Metro’s answer to Blue Line riders who have asked the transit authority to restore rush hour trains cut to make way for the Silver Line is: there is simply no more room.

The Rosslyn tunnel, the rail system’s worst chokepoint, can handle no more than 26 trains per rush hour. Now that Orange, Silver, and Blue are sharing the tracks, only five of those trains may be Blue Line. That's down from the seven per hour before the Silver Line opened.

But Metro often fails to reach its scheduled goal of 26 trains through Rosslyn, both in morning (inbound to D.C.) and afternoon (outbound to Va.) rush hours.

There are several reasons for less than optimal performance.

• Train or track problems: On August 6, a disabled train on the Orange Line forced single-tracking, sending delays rippling across the system. Only 14 outbound trains made it through Rosslyn between 6 and 7 p.m. that Wednesday, and only two were Blue Line.
• Crowding: It’s a vicious cycle: crowded trains take longer to unload and load once they arrive at the platform. This slows down the Blue/Orange/Silver parade, causing trains further down the line to become even more crowded.
• Manual operations: Because Metro’s trains have yet to return to Automatic Train Operation, individual operators are in control of acceleration and deceleration. Each operator drives a train differently, and some are more efficient than others at pulling into and then accelerating out of a station. Over the course of an hour, a few lost seconds per train adds up to an extra minute or two of delays.

According to data provided by Metro and compiled by MetroMinder DC, an app that measures the rail system's performance, in the first week of Silver Line service (July 28 through August 1), an average 25 outbound trains passed through the bottleneck between 5 to 6 p.m. Between 6 and 7 p.m., the average fell to 23.7 trains/hour.

In the second week (August 4 through August 8), an average 26 trains (the maximum) made it through the bottleneck between 5 and 6 p.m. The average dropped to 21.8 between 6 and 7 p.m., mostly as a result of the disabled train/single tracking on August 6.

MetroMinder compiled data for 24 separate peak-period hours during the afternoon rush outbound at Rosslyn from July 28 to August 13. Metro met the goal of five Blue Line trains 20 times.

Performance varies day to day. On Tuesday, July 29, between 5 and 6 p.m., 26 trains passed through Rosslyn into Virginia. On Wednesday, that number fell to 21, and then on Thursday rose to 24.

Commuters are bracing for the performance to potentially worsen after Labor Day, when vacationers and Congress eventually return to town and crank up the demand on the rail capacity.

On Wednesday, platforms at Rosslyn were relatively lightly crowded, not unusual for a mid-August workday. Metro squeezed 23 outbound trains through the tunnel between 5 and 6 p.m. Five were Blue Line.

Metro declined to comment on this story. In the weeks preceding the launch of the Silver Line, Metro urged Blue Line commuters to consider taking an Orange Line train to L'Enfant Plaza then transferring to a Yellow Line train to complete their commutes home in the afternoon.

But for the roughly 11,000 riders who travel from any one of the following: Rosslyn, Foggy Bottom, Farragut West, or Orange/Silver stations in Virginia to Blue Line stations in Virginia, one train every 12 minutes will be as good as it gets. For these riders, the Yellow Line does not make sense.

MetroMinder DC also compiled data for the inbound, morning commute through Rosslyn since the start of Silver Line service: an average 24 rush hour trains passed through the bottleneck in the first week, 26 trains an hour in the second, and 24 trains an hour so far this week. Metro considers morning rush hour to be 6:30 a.m. to 9 a.m.