THE SHORT ANSWER
Los Alamos Old Days runs September 25–27, 2026, and Caltrans says Highway 135 (Bell Street) in Los Alamos is fully closed from 7 a.m. to 4 p.m. on both Saturday, September 26 and Sunday, September 27 between St. Joseph Street and August Street.
The road closure is tied to the 80th annual festival. Caltrans says directional signs will be posted, travelers may experience delays of up to five minutes, and drivers should allow extra travel time and use alternate routes when possible.
WHAT IS ACTUALLY CLOSED
The official Caltrans notice is specific: the full closure is on Highway 135 / Bell Street between St. Joseph Street and August Street during the published 7 a.m.–4 p.m. windows on September 26 and 27.
Do not turn that localized event closure into a claim that Highway 101, every road in Los Alamos, nearby wineries, hotels, restaurants or the wider Santa Ynez Valley are closed. Check the exact route and destination involved in your trip.
THE EVENT ITSELF
The Los Alamos Valley Men's Club lists Old Days for September 25, 26 and 27, 2026 and describes the weekend as the event's 80th anniversary. Its official event page lists activities including a car show, artisan booths, food and beverage vendors, live music, a 5K run and a Sunday parade.
Those event listings are not a guarantee that every activity, vendor, ticket or parking option remains available when you arrive. Use the organizer's current schedule for event details and Caltrans for road information.
HOW TO PLAN A SATURDAY OR SUNDAY VISIT
If you are driving into Los Alamos during the 7 a.m.–4 p.m. closure window, expect Bell Street access to be different from an ordinary weekend. Build extra time into restaurant, tasting-room, lodging or event plans and follow posted traffic-control signs rather than relying only on a saved navigation route.
Caltrans says travelers may experience delays of up to five minutes. That is the agency's event-closure estimate, not a guaranteed trip time for every origin, parking location or itinerary.
If your route depends on Highway 135 shortly before, during or after the published closure period, check Caltrans QuickMap or current District 5 information before departure. An incident, weather issue or operational change can still affect travel independently of the scheduled festival closure.
AFTER 4 P.M. EACH DAY
The published Caltrans closure window ends at 4 p.m. on both Saturday and Sunday. Bon Voyage Compass will not assume the roadway has reopened exactly on schedule if current roadway information says otherwise, and it will not keep presenting this short-lived closure as active after the weekend without a new official source.
WHAT BON VOYAGE COMPASS WILL AND WILL NOT CLAIM
Bon Voyage Compass can combine the official festival dates with Caltrans's verified road-closure window into a practical trip-planning guide. It will not invent parking inventory, ticket availability, restaurant hours, hotel availability, detour travel times or business closures.
This guide was source-checked September 26, 2026 against Caltrans and the Los Alamos Valley Men's Club. Recheck both official sources before traveling because the event and traffic controls are time-sensitive.