It was built to the unique gauge of mm. Subsequent railway construction was predominantly metre gauge, resulting in an extensive network of lines in the Northeast, Southeast and South regions, with some penetration into the interior. In the 20th century a number of mm gauge lines were opened in the Southeast region, forming a network which was to become the predominant gauge in those states; a few lines were dual metre and mm gauge.
A number of mining railways, mostly in Minas Gerais, were built to mm gauge. A short section of one of these survives as a tourist railway. Some new railways are being built to standard mm gauge, notably various urban light rail projects. A very short section of standard gauge connects a metre gauge freight interchange near the Argentine border with the standard gauge network of Argentina.
There are long term proposals for new high speed lines, which would also be standard gauge, and the possibility of converting some or all of the mm gauge lines to standard gauge is being examined. The original metre gauge and mm gauge networks are largely intact; some sections which had closed have been or are being rehabilitated, and some new lines constructed. Following privatisation of the national network in the early 21st century, a number of companies operate the railways.
The network is now predominantly freight only; passenger services operate mainly in urban areas and on a just a few long distance lines. In , the goverment announced the creation of a new agency to oversee the creation of new freight and high speed passenger lines, which could amount to km of new construction over 30 years.
The last section of this line opened for service in An extension northwards to Vila do Conde is proposed, as is a southward extension of km to Panorama. In , certain legal difficulties were resolved, allowing proposals for a new km railway between Sinop and Miritituba to be progressed.
