Dear Dr. Gridlock:

I’ve been fed up with Metro’s long, long lapse of Orange Line trains from Vienna toward Metro Center during the midday, from about 10:30 a.m. to 2:30 p.m.

They run every 12 to 16 minutes. People still have classes, meetings and appointments to get to on time. I take the train from Virginia Square, and if I just miss one, I always have to wait at least 12 minutes.

There are no excuses from Metro about this lousy service; it’s been this way for the six years I’ve lived here.

But could Metro’s excuse be the Silver Line construction? The weekday service is almost as bad as the weekend, and that’s so bad I don’t use Metro on weekends.

— Patti Najarian, Arlington

 It’s not the Silver Line construction. That’s more of a factor on weekends. No, I’m afraid that what Najarian experiences is the way of life for midday riders on the outer portions of rail lines.

In July, the Metro board approved standards for the frequency of trains under normal conditions: At midday, trains are expected to run no more than six minutes apart in the rail system’s core and no more than 12 minutes apart in other segments.

At night, Metro expects trains in the core to run no more than 15 minutes apart and no more than 20 minutes apart in other areas.

In real life, the gaps between trains are not consistent. We’ve talked about the “scheduled adjustments” trains make by temporarily halting or skipping a station to eliminate big gaps. Checking the midday service on one recent day, I found gaps of 10 to 13 minutes between trains on the west side of the Orange Line.

If Najarian waits 16 minutes for a train, that would be four minutes beyond the midday standard. While the board approved the midday standard, it’s still unclear what the consequences will be for consistent violations of the standard.

Well, maybe one thing is clear: Metro doesn’t plan to offer refunds to riders for violations of standards. The board simply requires the transit staff, which developed the standard, to monitor adherence and report quarterly. (And who among us would want to set standards for ourselves if we also had to set penalties for violating them?)

If you’re wondering what’s in all this for you, the rider, you might be asking who’s lucky enough to be in the “core,” where trains are supposed to arrive no more than six minutes apart at midday.

That depends on the rail line. For Orange Line riders, it’s the central portion between Rosslyn and Stadium-Armory where they share tracks with the Blue Line. The “time between trains” standard counts the two lines together. So Blue Line riders are part of the core for that same stretch through the District.

They’re also in a six-minute zone between King Street and Pentagon, where they share the track with the Yellow Line trains.

The zone from Pentagon to Rosslyn, like the portion between Stadium-Armory and Largo Town Center, is subject to the 12-minute standard. On these tracks, the Blue Line runs alone.

You get the picture: Where service is beefed up because two lines come together, the standard says the gap should be no more than six minutes. The exception is the Red Line, the only one that doesn’t link up with another line somewhere along its route. The Red Line will be subject to the up-to-six-minutes standard between Shady Grove and Silver Spring. Between Silver Spring and the end of the line at Glenmont, it’s up to 12 minutes.

Mitigating factors: The setting of midday standards generated nothing like the concern riders showed about rush hour standards last year, and setting standards doesn’t change the current train schedule.

Also, you’ve got to be really unlucky to routinely wait the full 12 minutes. That would mean you consistently get to the platform in time to see the receding taillights of a train.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or e-mail