San Marcos SR-78 Eastbound Overnight Closures October 19–22: Exact Detour and Hours

Featured image: official SR-78 eastbound closure and ramp detour map, Caltrans District 11. For current conditions follow signage and QuickMap.

SAN MARCOS, SAN DIEGO COUNTY — OCTOBER 18, 2026. Drivers using eastbound State Route 78 through San Marcos should prepare for planned nighttime full closures at South Rancho Santa Fe Road from October 19 through October 22. Caltrans says the closure window is 10 p.m. to 5 a.m. so crews can replace roadway weight-in-motion sensors.

What exactly will close?

Caltrans District 11 says all eastbound SR-78 through lanes at South Rancho Santa Fe Road will be closed during the announced nighttime work windows. It is a specific eastbound closure point, not a reported full shutdown of the entire 17.7-mile corridor and not a permanent closure.

Official detour

Traffic will be directed off eastbound SR-78 at the South Rancho Santa Fe Road off-ramp and allowed to return to the highway using the South Rancho Santa Fe Road on-ramp, according to the official notice. Watch for portable electronic messages, construction personnel and signs on approach; do not rely exclusively on navigation software during a temporary freeway closure.

Dates and times

First announced overnight period: Monday, October 19, 2026, starting at 10 p.m.
Work continues: through Thursday, October 22, during the advertised 10 p.m.–5 a.m. nighttime windows.
Direction: Eastbound SR-78 at South Rancho Santa Fe Road, San Marcos.
Purpose: Replacement of weight-in-motion sensors associated with the SR-78 Asset Management Project.

Construction schedules can be modified because of weather, traffic incidents or other field conditions. Check conditions just before your trip, especially if you drive early in the morning.

Why are crews replacing roadway sensors?

The sensor replacement is part of the larger SR-78 Asset Management Project, which Caltrans describes as improvements along roughly 17.7 miles between Interstate 5 in Oceanside and Broadway/Lincoln Parkway in Escondido. The department puts the project estimate at $126 million, with a combination of federal and state funding. This is the overall project cost, not a claim that this four-night closure alone costs $126 million.

What to expect nearby

Caltrans warns of increased detour traffic, lighting, nighttime construction noise and backup alarms near the work zone. Businesses and residents close to the temporary detour may notice additional traffic while the interchange is used to redirect drivers.

What changes for residents?

People returning from evening shifts, delivery drivers and visitors heading east from the coast may encounter unexpected exits and delays. Leave more time, follow posted routing and watch for highway crews. For urgent route verification use Caltrans QuickMap. Caltrans District 11 lists CT.Public.Information.D11@dot.ca.gov and (619) 688-6670 for project information.

Earlier in October, California58 also reported on separate westbound SR-78 nighttime closures. Those earlier dates and direction should not be confused with the eastbound October 19–22 schedule.

Primary source: Caltrans District 11, October 16, 2026 notice. These are announced future closures, not independently observed live road conditions.