Riders on the Franconia-Springfield platform wait for a train during a morning rush. (Robert Thomson/The Washington Post)

Metro is sending out advisories to riders about its plans to test the Silver Line trains next week, before the line’s scheduled opening on July 26.

While the testing begins this Sunday, the real impact on commuters will come on Monday. That’s the day when the Rush Plus Orange Line disappears and two Blue Line trains get shifted over to the Yellow Line.

Some riders — especially on the Blue Line — have been dreading the start of the Silver Line, because of the subtractions on the other lines. But the upcoming week of “simulated service” adds an extra challenge for some: The Silver Line won’t be operating as “the Silver Line.”

Starting Sunday, test trains will leave the new Wiehle-Reston East station, travel without passengers through the four stations in Tysons Corner, then join the Orange Line at the East Falls Church station. At that point, they will become Orange Line trains and take on passengers. They will continue east as Orange Line trains Largo Town Center. Then they will turn back west — still as Orange Line trains — to East Falls Church. That’s where all passengers will have to get off and wait for the next Orange Line train toward Vienna. Meanwhile, the out of service train will continue up the new Silver Line tracks to complete the test run.

Starting with the Monday rush, these test trains are scheduled to operate every six minutes at peak periods. If you board a train at East Falls Church, or Clarendon or Rosslyn for a trip downtown, you should be fine with this. Your stations will either have a couple more trains per hour during the rush or the same number of trains. In fact, you should watch for some trains that may be less crowded than usual because they started taking on passengers at East Falls Church, rather than Vienna. These would be the Orange Line trains with the “Largo” destination signs.

But if you board trains at Vienna, Dunn Loring or West Falls Church, it’s a different story. You will go back to the level of service before Rush Plus added trains back in 2012. Trains should reach your platforms about every six minutes, Metro says.

In the plans developed by Metro and the Fairfax County Department of Transportation, many riders who now use those outer stations on the Orange Line will begin using the five new Silver Line stations. But there’s this one-week gap during the simulated service when they won’t have that option.

When I asked Metro General Manager Richard Sarles if the transit authority anticipated a problem with crowding on those west-end platforms, he noted that we will be deep into summer. “A lot of people take vacation, he said. “We expect ridership will be down in general,” making extra crowding a less likely prospect.

How about if you are traveling east to west on the Orange Line next week? The same number of trains as today are scheduled to leave from New Carrollton during the morning rush. From Largo Town Center, riders will have five more trains per hour. But they’ll need to know it’s okay to board an Orange Line train with a destination sign that says “East Falls Church.” Those trains will take them to destinations in downtown Washington and then out along the Orange Line tracks to East Falls Church.

Leaving downtown during the afternoon rush: Orange Line riders heading home to West Falls Church, Dunn Loring or Vienna will wait longer than today for a train marked “Vienna.” They may be better off boarding a train marked “East Falls Church” (meaning it’s one of the Silver Line test trains), then getting off the train along with everyone else at East Falls Church. The next Vienna-bound train reaching the East Falls Church platform is likely to be much less crowded than the one they would have boarded when they were downtown.

If you’re heading back to New Carrollton from downtown, you’ll have less frequent service starting next week. The number of trains per hour during the rush will drop from 14 to 11 per hour between Minnesota Avenue and New Carrollton.

How about if you use a Blue Line platform in Virginia? Starting next week, you will find the rush hour trains arriving 12 minutes apart. The primary impact is on riders bound for stations on the west side of the District, or who transfer at Rosslyn and head west along the Orange Line.

If you consistently wait 12 minutes for a train, you’re really unlucky, because it means you consistently reach the platform in time to see a train pulling out of the station. You might consider changing your schedule or your karma. The average wait for riders will be more like six minutes.

I say that not to minimize the impact on the thousands of daily riders heading for those Blue Line destinations, but rather to suggest that the biggest impact of fewer trains might be greater crowding on the remaining five trains per hour. Metro says half the Blue Line trains during the rush will now be eight cars long, rather than six.

With five trains per hour, what does Metro mean by “half”? It means that six of the 12 train sets used for Blue Line service will be eight-cars long. To me, this is the big impact of the bigger gaps between Blue Line trains: You will have a 50-50 chance of boarding an eight-car train. If the next-train board on the platform says the next Blue Line train is eight cars, and you’ve got one on the platform that’s six, you’re probably going to try to squeeze aboard that rather than wait 12 minutes for a little more space.

The Yellow Line gets two more trains per hour starting with Monday morning’s rush. To see if switching from the Blue to Yellow will work for you, see this posting by Lori Aratani. This is the last remaining part of Rush Plus service. These extra Yellow Line trains will operate between Franconia-Springfield and Greenbelt at peak periods.