Some train stops are out of service, and there are limits to what passengers can bring board.
It is also likely that some passengers could be searched.
The Metra stations that are closed Saturday and Sunday are the 11th Street museum campus, McCormick Place, 18th Street, 27th Street 47th Street stations.
Also, anyone planning to take a Metra train downtown is advised that only one small bag is allowed on board, and it has to be smaller than 15 inches.
Additionally, no backpacks, liquids or food will be allowed.
Passenger Jonathan Petzold was not aware of the backpack rule. He was not permitted to board a Saturday morning train leaving from Hyde Park.
"They obviously seem to think they are, and for a couple days, I mean, most people are avoiding it. I can't. I have to get to work, but for a couple days we can endure it," Petzold said.
Signs are posted on the Metra platforms to remind passengers about the prohibited items.
On Monday as well, a number of stations will be closed and the trains will stop running entirely for several hours in the afternoon the Metra Electric line, which runs under McCormick Place.
Those station closures include the 11th Street museum campus, McCormick Place, 18th Street, 27th Street 47th Street stations, as well as the 87th Street and Blue Island stations.
Volume on trains was a lot lighter than usual during Friday afternoon's commute. Many passengers just decided to stay away from downtown during this summit weekend. Some commuters, however, were dreading Monday morning.
"I think Monday is going to be a problem, so, you just got to deal with it," Metra rider Bill Cerva said.
"It changes the way I prepare for work," said commuter Cavin Armour.
Metra passengers are advised to arrive an extra 15 minutes earlier to their stations because extensive security screenings will be under way.