US-101/Olive Mill Road & San Ysidro Interchanges

Mark Thomas provided final design services for two single-lane roundabouts constructed at Olive Mill Road and San Ysidro Road, improving traffic operations and safety at key intersections connected to Highway 101. The Olive Mill Roundabout serves a five-leg intersection including Olive Mill Road, Coast Village Road, North Jameson Lane, and the northbound off-ramp and southbound on-ramp of Highway 101. The San Ysidro Roundabout improves circulation at the intersection of San Ysidro Road, North Jameson Lane, and the northbound Highway 101 on- and off-ramps.

Services included geometric and civil design, drainage, utility coordination, stakeholder engagement, right of way support, and Coastal Development Permit (CDP) processing. The project required coordination with Caltrans and local agencies and was delivered within the context of broader US 101 corridor improvements. It was on an accelerated delivery model using CMGC.

Each roundabout incorporates design elements that support traffic operations, freight movement, and multimodal safety. Features include landscaped centers with olive or sycamore trees, sandstone retaining walls, cobblestone truck aprons, enhanced lighting, and new pedestrian crosswalks with refuge medians. Bicyclists are accommodated through shared-lane use or by walking bikes along sidewalks and crosswalks. Design and construction were completed within constrained rights of way, with careful attention to phasing and community impact.