Over a mile of guardrails will be replaced next summer in 13 places in West Marin. Locations include Marshall-Petaluma Road, Point Reyes-Petaluma Road, Tomales-Petaluma Road and Panoramic Highway. The $961,200 project is fully funded by a federal grant from the highway safety improvement program. The locations were chosen based on a five-year study of collision trends in Marin, which looked at all 2,756 crashes from 2012 to 2016, with a specific focus on collisions that…