Highway officials are closing the Zurquí tunnel on Ruta 32 for seven hours Saturday at 6 a.m.
Workers will be putting down asphalt and doing other road-related work.
The 600-meter tunnel is the only route on the highway, which is the main road from San José to the north and then to the Caribbean coast. The tunnel itself is nearly 2,000 feet, but there will be work outside on either end, said the Consejo Nacional de Vialidad.
The work is part of the job to put down new lines for lanes on much of the roadway.