The railroad continued to be in use under American rule for most of the first half of the 20th century and played a key role in the transportation of people and goods throughout the island.

During its heyday, it was the most modern electric streetcar system in Puerto Rico, rivaled New York and Toronto, and transported nearly 10 million passengers a year.

Automobiles became more widely available, and more efficient roads and highways and the closure of sugarcane mills displaced the need for rail transportation.

Soon, it was realized that an alternative means of mass transportation was needed to complement the public bus system to alleviate the severe traffic situation that was being created, especially in the San Juan metropolitan area.

study, funded jointly by the Puerto Rico Planning Board and the US federal government, recommended an islandwide elevated transit system and new community development program.

That proposal would have served the San Juan metropolitan area and connected it with the rest of the island without the necessity of highway construction.

However, it was not until 1989 that the Puerto Rico Department of Transportation and Public Works (Departamento de Transportación y Obras Públicas, or DTOP in Spanish) officially adopted a proposal to begin design and construction of a rail system for the San Juan metropolitan area.

By 1992, various alignments of the proposed system were considered, but the final design chosen served only certain parts of the metro area and did not include Old San Juan.

In 1993, the Federal Transit Administration (FTA) selected it as a Turnkey Demonstration Project under the Intermodal Surface Transportation Efficiency Act of 1991.

The construction project was plagued by delays, contractual disputes between the government and companies involved in the undertaking, and investigations into possible mismanagement of funds.

[9] The Tren Urbano has no service to Old San Juan, Santurce, Luis Muñoz Marín International Airport or to many other parts of Guaynabo, Bayamón, and San Juan, and it does not serve important suburbs like Cataño, Toa Baja, Toa Alta, Carolina, Trujillo Alto, and Canóvanas, limiting ridership.

Integration with other transit systems, such as the AMA and the AcuaExpreso (an urban ferry), was initially poor and remains a challenge for the DTOP.

[11] Power is provided by AC traction motors, which were chosen over DC since they contain fewer moving parts and require less maintenance.

Rolling stock for Tren Urbano metro cars are stored at the Hogar del Niño Operations and Maintenance Building, near the exit to PR-21 from PR-20 and a short distance from Martínez Nadal station.

With a fleet of 74 rail vehicles in the local yard to cover at least twice the 10.7-mile (17.2-km) system length, the basic facilities and capital equipment needed for expansion are in place.