When the Ironman triathletes reach Santa Rosa, these are the places drivers should avoid

You would be smart to avoid Highway 12 west of Santa Rosa today when 2,400 Ironman competitors cross the normally busy thoroughfare - twice.

Highway 12 at Irwin Lane ranks among the places with the biggest potential for traffic jams Saturday during the 112-mile cycling portion of the triathlon, according to city officials David Guhin and Adriane Mertens. Even so, the cycling course could present other obstacles for motorists. For example:

Northbound Santa Rosa Avenue will be blocked at Petaluma Hill Road.

Motorists won’t be able to cross the racecourse at major intersections on West Third Street and for a long stretch of Petaluma Hill Road inside the city.

Along with Highway 12, the cyclists will stop traffic when making left turns from Laguna Road onto Guerneville Road west of the city and from Mountain View Avenue onto Santa Rosa Avenue near Rohnert Park.

The cycling portion, the second leg of the race, starts at Lake Sonoma. There, at 6:10 a.m. the first entrants will start the competition with a 2.4-mile swim in the lake near the Rockpile Road bridge. After swimming, the racers will hop on bikes, head north toward Cloverdale and eventually turn south for Santa Rosa.

The cyclists will make two laps around southern Santa Rosa, the northern edge of Rohnert Park and along country roads near the Laguna de Santa Rosa. When they have finished cycling, the entrants will ditch their bikes at Old Courthouse Square and run 26.2 miles along the Prince Memorial Greenway and the Santa Rosa Creek Trail. The course to Fulton Road and back to downtown will keep the runners largely separated from traffic as they make three laps out and back.

The last contestants are expected to finish about midnight.

Within the city, motorists from 9 a.m. to 5:30 p.m. should avoid West Third and Petaluma Hill, said Guhin, an assistant city manager, and Mertens, a market and outreach coordinator with the Planning & Economic Development Department. Within the city, motorists can detour onto Highway 12 or College Avenue and use Highway 101 for north-south travel.

Motorists also should consider avoiding Highway 12 between Fulton Road and Sebastopol between roughly 10:30 a.m. and 5 p.m. Guhin advised using a detour of highways 101 and 116.

He said the city and race officials have tried to reduce the impact on residents. The city mailed out 5,000 notifications to Santa Rosans who live near the race course. City residents also received inserts into their monthly water bills.

The race officials also scheduled the race so the roads around wineries in the north county will open for normal traffic by 10:30 a.m.

Residents can learn more about detours and other race information at srcity.org/ironman. Live traffic assistance is also available on mobile devices using the Waze traffic app.

Ironman race director Dave Reid spoke Friday from Lake Sonoma, where the entrants were bringing their bikes to be ready for the cycling leg. He said the event’s many components were coming together well for Saturday’s start.

“We’ll be ready and it will be a great day,” Reid said.

You can reach Staff Writer Robert Digitale at 707-521-5285 or robert.digitale@pressdemocrat.com. On Twitter @rdigit.