The Sonoma County Board of Supervisors Tuesday lowered the speed limit on a stretch of Petaluma Hill Road approaching Santa Rosa and just south of the spot where a 6-year-old girl in a crosswalk was struck by a motorist Sunday and seriously injured.

The change from 55 to 45 mph was to accommodate a new entrance to Taylor Mountain Regional Park and was not a reaction to Sunday’s accident. But traffic officials said it would help reduce speeds on Santa Rosa streets.

“It’s good to have a gradual step down in speed before you get to the city,” said Rob Sprinkle, Santa Rosa’s traffic engineer.

The speed limit on the major county road that connects Penngrove and Santa Rosa will now be reduced to 45 mph about three-quarters of a mile south of the Santa Rosa city limits near the planned entrance area to the park, which will include turning lanes when it opens this spring. The speed limit at the city limits is already 45 mph and drops to 40 mph north of Kawana Springs Road.

The 6-year-old girl was hit Sunday while using a crosswalk with her mother at Breeze Way.

Supervisor Shirlee Zane said the road is notorious for speeders, especially in the unincorporated county.

“People speed. I’m very familiar with this major collector (road),” Zane said. “I know most people go 60 to 65 on that stretch.”

Petaluma Hill Road carries 14,000 cars per day, according to a county report. There have been five collisions on the section between Santa Rosa and Taylor Mountain Regional Park in the past four years.

“We believe that by reducing the speed limit, we will reduce the number of collisions that occur in that location,” said Jason Nutt, deputy director of the county Transportation and Public Works Department.