All points in the western Central Valley can be reached by car. For San Antonio de Belén, Heredia, Alajuela, and points north of San José, turn right at the west end of Paseo Colón onto the Pan-American Highway (Autopista General Cañas). The eastern Central Valley is accessible from San José by driving east on Avenidas 2, then Central, through San Pedro, then following signs from the intersection to Cartago. To get to the Orosi Valley, head straight through Cartago, turn right at the Basílica de Los Angeles, and follow the signs to Paraíso. The road through Cartago and Paraíso continues east to Turrialba. Driving from one side of the valley to the other means you need to get across San José. There's no truly efficient way to bypass the capital.
The best way to get around the Central Valley is by car. Most of the car-rental agencies in San José have offices at or near the airport in Alajuela. They will deliver vehicles to many area hotels, but not those in Turrialba and the Orosi Valley.