SAN FRANCISCO (KGO) --Thousands of people are in San Francisco are getting ready for one of the world's most unique races.
Bay to Breakers returns Sunday for its 105th year and the city is preparing to control the chaos.
WATCH LIVE: Bay to Breakers race live starting at 8 a.m. on Sunday
As runners and other participants gear up for their cross-city trek, race organizers will begin setting up the route Saturday night.
The race expo already closed for the afternoon Saturday but there were thousands of people who were there picking up their bibs and racing shirts.
PHOTOS: Bay to Breakers costume ideas
Bay to Breakers may be the silliest running event in the county, but it's also one of the oldest city races in the U.S.
Crews already have lots of barriers ready to haul into place along the route. They will shut down Howard Street between the Embarcardero and Main Street at about 7 p.m. so they can set up the starting line. The rest of the route will be assembled overnight.
The race brings out serious runners and more leisurely revelers every year.
"You've got people from all over the country coming here to race it, and it's a great course to because there's nothing like running through San Francisco," said runner Michelle Reyes.
"I did it two years ago, with one of my best friends, I was living here at the time and we had a blast. And I figured, what the heck, why not do it again?" said Los Angeles resident Demetra Markopoulos.
VIDEO: 7 Things to know about Bay to Breakers
As usual, runners are welcomed to come in costume, but they will not be able to bring any kind of backpack. As a security precaution after the bombing at the Boston Marathon, police officers and security workers will not allow backpacks on, or near the course.
There are roughly 40,000 registered participants for Sunday's race. Runners start the Bay to Breakers race at 8 a.m. at Howard and Main streets near San Francisco Bay and run west to The Great Highway and the Pacific Ocean breakers at Ocean Beach.
The race ends on The Great Highway just north of Lincoln Way. The runners race up the Hayes Street Hill, one of the most notorious hills in all of racing, according to race organizers. The race also takes runners through Golden Gate Park.
Bay to Breakers is the oldest annual footrace in the world. It began in 1912.
The weather forecast is temperatures will be in the 50s for the beginning of the race and rise to 60 to 65 degrees by afternoon. Runners can expect low clouds, drizzle and fog at the start of the race.
Last year 29,971 people finished the race. About 16,000 women finished and nearly 14,000 men.
Two Kenyans won the race last year. Isaac Mukundi Mwangi won the Men's Elite Division and Jane Kibii had the fastest time overall among women.
BART and Caltrain have added service to get runners to the starting line.
Caltrain will run four special northbound trains. The Special A train will depart the Palo Alto station at 6:12 a.m. and arrive in San Francisco at Fourth and King streets at 6:55 a.m.
The Special B train will leave San Jose's Diridon station at 5:50 a.m. and arrive at the Fourth and King streets station at 7:04 a.m. The Special C train will depart the Diridon station at 6:04 a.m. and arrive at Fourth and King streets at 7:21 a.m.
The Special D train will leave at 6:31 a.m. from San Jose's Diridon station and arrive at Fourth and King streets at 7:55 a.m.
No alcohol is allowed on the special trains. San Francisco's Municipal Railway T-Third line can take passengers to the starting line or runners can walk.
After the race, three express trains depart for Belmont at 1:10 p.m., 2:10 p.m. and 3:10 p.m. After Belmont, the trains will make regular weekend stops to the San Jose Diridon station.
PHOTOS: PHOTOS: Thousands run through heart of San Francisco for the 2015 Bay to Breakers
BART will start operating at 6 a.m. with trains running at 20-minute intervals before 8 a.m. BART officials are encouraging runners coming from the Peninsula to off-board at Montgomery station because of the number of people who attend the race. Runners from the East Bay are being encouraged to off-board at the Embarcadero station. Both stations are close to the starting line.
Bay City News contributed to this report.
ABC7 will live steam the entire race starting at 8 a.m. on Sunday. Check back here Sunday morning for updates.