El Sillar is a 28-kilometer section of the RN4 highway that connects the Bolivian cities of Cochabamba and Santa Cruz de la Sierra. This section runs through a mountain pass in the Amazon rainforest and its doubling will involve the construction of 29 bridges and viaducts and two tunnels of 1,700 m and 1,100 m respectively.
The extension of the El Sillar dual carriageway, which was built at the end of the 1960s, will make it possible to facilitate transit by the main transport axis of the country La Paz-Cochabamba-Santa Cruz de la Sierra.
The works, promoted by the Bolivian Highway Authority (ABC), are being built by the Chinese company Sinohydro and financed by the Bolivian government.