BOSTON (CBS) – It’s the same familiar streets and the same familiar route. But everything else about this year’s 125th running of the Boston Marathon will feel a little different.

“We reduced the field size by 40%, eliminated the Athletes Village and we’ll have a rolling start for the first time,” said Thomas Grilk, CEO of the Boston Athletic Association, during a Thursday press conference.

READ MORE: Nearly 15,400 Runners Crossed The 125th Boston Marathon Finish Line

The reduced field means some 20,000 runners will take to the course instead of 31,500, and some will be running virtually. The goal is to prevent athletes from congregating, and to allow for social distancing.

The rolling start means that in Hopkinton runners will get off buses that delivered them from Boston. They are encouraged to immediately hit the route.

Runners will have been required to show proof of vaccination.

READ MORE: Boston Marathon Returns To Patriots' Day In 2022

“If they don’t, and 95% of them will, then they will have to get a COVID test,” said Dr. Pierre D’hemecourt, a sports medicine physician and co-medical director of the race.

What officials can’t say is how they’ll prevent spectators from congregating in large groups to cheer the runners on.

It’s been two years since the running of the Boston Marathon due to the pandemic and it’s heightened the excitement as well as the preparation. Grilk said race officials can only encourage people to follow safety protocols.

“When it comes to people taking care of themselves and social distancing and wearing masks, we can’t make them do anything,” he said.

MORE NEWS: VIDEO: Highlights From 2021 Boston Marathon

You can watch the Boston Marathon live on Monday, October 11 on CBSBoston.com and WBZ-TV. Coverage starts at 4:30 a.m.

Beth Germano