On SR 4, the detour is now part of the trip

State Route 4 is not a through road across this part of California's Delta this weekend. Caltrans has closed the highway in both directions from Roberts Road to the San Joaquin-Contra Costa county line, east of Discovery Bay, until 5 a.m. Monday, August 17. Local residents and customers can reach homes and businesses inside the closure limits, but other traffic must leave the corridor.

The official detour is a regional loop rather than a turn around one work crew. Westbound travelers are directed south on Roberts Road, west on Howard Road, south on Tracy Boulevard, west on Interstate 205, then north by Mountain House Parkway and Byron Road to regain SR 4. Eastbound travelers use that sequence in reverse, starting south on Byron Road and Mountain House Parkway before taking I-205 east toward Tracy Boulevard, Howard Road and Roberts Road.

Caltrans says the signed route may add about 30 to 40 minutes. The practical cost can spread further when a fuel stop, appointment, service call or delivery was planned around the two-lane highway. That wider schedule effect is an inference from the detour length, not a prediction for an individual trip; traffic, incidents and the pace of the work can change the result.

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This is an additional 55-hour closure, not the first one in the project. Caltrans says crews used earlier weekend closures in July and found more pavement and subsurface failures that require repair. The broader $21.6 million Delta pavement project covers roughly nine miles between the county line and South Whiskey Slough Road, with failed areas excavated before new pavement and related roadway systems are installed. Completion is expected in February 2027.

Monday's planned reopening also does not remove every restriction from the route. A separate Caltrans advisory calls for continuous one-way traffic control at Old River Bridge through November. Vehicles longer than 34 feet are strongly encouraged to use another route, with SR 12 or I-205 listed as highway alternatives between Discovery Bay and Stockton. That length guidance belongs in the plan before a large vehicle reaches the bridge approach.

The distinction matters: the full closure is a weekend condition with a required detour, while the bridge control is a longer one-lane condition with special advice for longer vehicles. Saving only Monday's reopening time can erase the second part of the route brief. A trip after 5 a.m. still needs the current bridge status and a realistic allowance for alternating traffic.

Before departure, check Caltrans QuickMap, confirm whether the full closure has actually lifted, and keep the signed route separate from any local suggestion offered by a navigation app. If conditions change while moving, a passenger or someone at the destination can handle the update. On this Delta corridor, the safest short cut is the planning done before the road narrows or ends.