Sections of about 20 city and county roads will be closed temporarily Sunday as about 2,800 runners pound the pavement during the inaugural San Luis Obispo Marathon and half marathon.

The marathon — the first held in the city in 26 years — will affect numerous roads in downtown San Luis Obispo, as well as in much of the southeastern part of the city and Edna Valley, starting early that morning and, for some roads, extending into the afternoon.

Some streets in San Luis Obispo will be closed completely while the crowds of runners wind their way around downtown early Sunday. Most other streets will be closed to through traffic, except for those with proof of residency, such as a driver’s license with a current address. The freeway on- and off-ramps at Marsh Street and Highway 101 will be closed the longest, from 4 a.m. to 3 p.m.

“We hope the positives outweigh some of the temporary inconveniences of the day,” event director Heather Hellman of Get Off The Couch Potato Sports Productions recently told the San Luis Obispo City Council.

About 800 marathon and 2,000 half-marathon participants will follow a loop course that starts at San Luis Obispo High School, heads through downtown and reaches out into the rolling hills of Edna Valley before it comes back to town and finishes at the Madonna Inn.

Over the past few weeks, race organizers have set up signs notifying drivers of the upcoming closures and mailed notifications to 6,200 residents and business owners.

They also hand-delivered or mailed a second notification to 650 city and county residents to clarify the closures and reassure residents that they will have access to their homes.

Race organizers suggest the best place for spectators is at the finish line because the course is closed to the public. Parking will be available at the Madonna Inn.

On Sunday, San Luis Obispo police, CHP officers and about 150 volunteer course marshals will help direct traffic and ensure runners’ safety on the course.

In the downtown area, officials plan rolling closures, meaning once runners are clear from a stretch, that road will reopen, said San Luis Obispo traffic engineer Matt Crisp. Most streets in the downtown core should be open by 8 a.m.

Still, the closures concern some residents, many of whom live along Orcutt Road, which will be closed to through traffic starting at 6 a.m. Sunday.

Some are worried they won’t be able to get to work or church, and they wondered how the closure might hurt local wineries or other businesses.

“We deal with people practicing on the road, and it’s narrow,” said Mike Jones, who lives on Orcutt Road in an area that will be closed to through traffic from 6 a.m. to 1 p.m. “We’ve had the (SLO Triathlon) out here every year, and now they’re adding another one on to it — that’s an inconvenience.”

The stretch of Orcutt Road between Johnson Avenue and Tank Farm Road will have one lane of traffic open only for local residents.

The section of Orcutt Road between Tank Farm and Biddle Ranch roads will be closed because there is no line of sight for drivers among the rolling hills and curving roadway, said Samantha Pruitt, who with Hellman founded Get Off The Couch Potato Sports Productions.

“We’re trying to do No. 1, athlete safety, and No. 2, keep the residents happy,” she said.

City and county officials acknowledged residents’ concerns and said they worked with the race organizers to ensure people have access to their properties.

The impact to downtown businesses should be less than that of when cyclists with the Amgen Tour of California rode into town, or when downtown streets are closed for the annual holiday parade, Crisp said.

“Yes there are some impacts,” added Dave Flynn, deputy director of the county’s Public Works Department. “Hopefully we can minimize it so events like this can go forward.”