After several years of study, the transit authority has decided how it wants to rearrange the Metrorail trains. Now Metro’s task is to explain this new rush-hour service so people can take advantage of it, or at least avoid getting lost.

What’s changing?

Starting in June, the peak period service will include more Orange Line trains coming from the line’s western end in Northern Virginia into downtown Washington. Fewer Blue Line trains will serve the downtown’s west side. More trains from Northern Virginia will serve the downtown’s east side. Those trains will arrive in the District at L’Enfant Plaza and continue north to Greenbelt in Prince George’s County.

Why change?

Metrorail commuters develop habits. They don’t need to look at a map for directions. They don’t need to pull out their earbuds to hear announcements. They know where to stand on the platform to board the rail car that’s going to wind up closest to the station escalator that’s closest to their office.

Why mess with that?

Three reasons: Ridership on the eastern side of downtown is growing faster than on the western side. Rush-hour trains entering the Rosslyn tunnel from Virginia into the District are jammed. The tunnel is handling the maximum number of trains — 26 per hour at peak periods — and in two years, Metro will need to find a way to squeeze in trains coming down the new Silver Line.

But if the Silver Line won’t be ready till 2013, why does Metro want to make these changes in the middle of 2012?

Two reasons: One is to let riders get used to the new patterns. This is the biggest change in train origins and destinations since the original system was completed. The other reason is that Metro officials want time to see how riders respond, and possibly make adjustments.

The transit staff expects a certain percentage of Blue and Yellow Line riders to alter their behavior. Metro estimates that somewhere between 20 and 33 percent of today’s Blue Line riders will shift to Yellow Line trains. Exactly how many do that and where could affect crowding.

Who gains?

Overall, Metro officials say, the changes are going to help a lot more riders than they hurt. The staff’s rough estimate is that 108,000 riders will benefit from service increases and time savings. That accounts for 43 percent of the trips made at peak periods.

Orange Line riders in Northern Virginia who have to let several inbound trains pass them by in the morning before they find space to cram aboard should find less crowding thanks to three more trains per hour at peak periods from West Falls Church.

Today’s Blue Line riders who follow a circuitous route through Rosslyn to reach offices on the east side of downtown will have access to extra trains taking the shorter route across the Potomac River bridge into L’Enfant Plaza. Those extra trains will be marked as Yellow Line trains, and they will travel between Franconia-Springfield and Greenbelt. That means that at rush hours, the Yellow Line will have two terminals in Virginia, the traditional one at Huntington and the new one at Franconia-Springfield.

Green Line riders who crave more rush-hour service on the central corridor between Mount Vernon Square and Greenbelt will now have it, thanks to the addition of Yellow Line trains at the peak periods.

Who loses?

The transit staff estimates that 16,000 riders, or about 6 percent of those traveling at peak periods, will be inconvenienced. A third of the Blue Line trains will become Yellow Line trains at rush hour. That’s not a problem for those who board at the Franconia-Springfield terminal and make the short trip to Crystal City or the Pentagon. It is an issue for those who go on to Rosslyn, or Foggy Bottom or Farragut West.

A rush-hour rider who just misses a Blue Line train departing from Franconia Springfield would wait six minutes for the next one, then six minutes for the one after that. But the next one would leave 12 minutes later.

Riders heading for Rosslyn could just get on the new Yellow Line train and ride it up the line to a station where they could transfer to the Blue Line. If they were determined instead to have a one-seat ride, they would have to look sharp to make sure they were boarding a Blue Line train and not a Yellow, and they would have to know the schedule well enough to reach the station when a Blue Line train is next in line to depart.

There will be fewer Blue Line trains at rush hour serving the eastern side of the line, which terminates at Largo Town Center. But Metro says the level of rush-hour service will stay the same, because those new Orange Line trains from Northern Virginia will continue on to Largo.

What’s ahead?

“There’s going to be some pain with this. There’s going to be some customer confusion,” Metro Board Member Jeff McKay of Fairfax County said before the board ratified the change Thursday. But he added that the change “has to happen.”

The change involves challenges for Metro, and McKay described a key element: “It’s never been more important to provide accurate information.”

Tom Harrington, a transit authority planner, said Metro could look at doing more to help riders adjust through the Trip Planner scheduling tool on its Web site, as well as with the real-time information it sends electronically to riders.

Assistant General Manager Barbara Richardson said this month that Metro is preparing an extensive campaign — a “constant drum beat” — to get riders familiar with the upcoming changes. It will start early next year and become even more visible in the spring. Metro has involved riders in the planning. For example, Richardson said, riders did not want the new services designated with new colors. Their message was “Do not introduce a new color line unless you are literally constructing a new rail line,” she said. So the Dulles line will be marked in silver, but the new services will be shown with dashes at the ends of the appropriate lines.

Metro needed more than half a year’s lead time following board approval because of the scope of the information campaign. It’s not just the system maps that need to be modified. All the station signs and fare charts also need changes.

Riders’ Advisory Council Chairman Frank DeBernardo expressed the council’s concern that the communication strategies take into account riders with visual or auditory disabilities.

Metro has not announced any specific plans regarding passengers with disabilities, but it has promised that the communications program will be “multi-sensory.”