Grant Line Road Roundabouts Project

The Grant Line Road Roundabouts Project, led by the City of Mountain House in Alameda County, involves the construction of roundabouts at two key intersections along West Grant Line Road: one at Altamont Pass Road and another at Mountain House Road. The primary objective is to reduce excessive queuing and traffic delays, though the designs are not intended to accommodate future forecasted traffic volumes. The project requires the acquisition of additional road right-of-way and formal approvals from both the City and Alameda County. Technical specifications for the Altamont Pass Road intersection include a 53-foot diameter roundabout with a 13-foot truck apron, a 16-foot wide asphalt travel lane, and the installation of a 270-foot concrete median on the westbound approach. Environmental compliance is a critical component of the project, as it is subject to the California Environmental Quality Act and requires permits from the USFWS, CDFW, and the Army Corps of Engineers due to the proximity of Mountain House Creek. Strict construction mandates include scheduling work during the dry season, prohibiting activity during significant rain events, and maintaining refueling areas at least 100 feet from the creek. Additionally, the project must address risks associated with previously abandoned oil and gas wells as advised by CalGEM and implement specific mitigation measures for traffic hazards and tribal cultural resources. Public review of the Draft Environmental Impact Report was conducted between September 19 and November 3, 2025.