OLD ORCHARD BEACH – Hundreds of triathletes, including about 40 professionals, are expected to compete on – and just off – Old Orchard Beach Sunday in the Revolution 3 Triathlon.

The event will begin about 6:20 a.m. with a swim, followed by a bike ride and a run.

Professionals will compete for a share of a $25,000 purse, while the rest will be going after bragging rights.

There are two classes – the Olympic Rev and the Half Rev. Contrary to what you might expect, the Half Rev is the more strenuous of the two and will also be the race in which the professionals will compete.

The Olympic Rev consists of a swim of nearly a mile from the Old Orchard Beach pier to the section of the beach near Bay Avenue. It’s followed by a 25-mile bike ride and a 6.2-mile run.

The Half Rev is a slightly longer swim of 1.2 miles, a 56-mile bike ride, from Old Orchard Beach to Waterboro and back, and a 13.1 mile run.

The event will require significant road closings in the area, including First Street, which will be closed to traffic from Staples Street to Heath Street until 6 p.m. Sunday.

Police will also be posted to control traffic at intersections in Old Orchard, Scarborough, Saco and Dayton. Because the bike portion crosses Route 1 near Old Orchard Beach and Saco, motorists are encourage to avoid that road between 7 a.m. and 11:30 a.m. Sunday.