Key Facts
—The project. Rio Metro Line 3 would be the state’s first intercity line, linking the capital to Niterói and São Gonçalo under Guanabara Bay.
—The scale. The preliminary route spans about 50 km with roughly 29 stations, reaching Itaboraí.
—The time saving. A Coppe/UFRJ study estimates an Icaraí–Santos Dumont trip would drop from about 75 minutes to 11, an 85 percent cut.
—The demand. Earlier projections put daily ridership for the corridor at around 650,000 passengers.
—The history. The line has been promised since the 1970s; a 2011 federal pledge stalled and a 2023 study tender was annulled.
—The hook. The revival is tied to Rio and Niterói’s bid to host the 2031 Pan-American Games.
A new university study has revived Rio Metro Line 3, the decades-old dream of a rail tunnel under Guanabara Bay, now tied to the city’s bid to host the 2031 Pan-American Games.
Some infrastructure projects are promised so often they become folklore. In Rio de Janeiro, a metro line under Guanabara Bay is one of them.
The idea has been floated since the 1970s and never built. Now a fresh technical study has put it back on the table, with new numbers that make the case hard to ignore.
Researchers at Coppe, the engineering institute of the Federal University of Rio de Janeiro, presented the latest results of the Prisma study in early June. It is the most detailed look yet at how the line might actually work.
What Rio Metro Line 3 would do
The plan is for Rio’s first intercity metro line. It would link the capital to Niterói and São Gonçalo, two populous cities across the bay that today depend on ferries, buses and a congested bridge.
The preliminary route runs about 50 kilometres with some 29 stations, reaching as far as Itaboraí to the east. The centrepiece is an underwater tunnel beneath Guanabara Bay, linking central Rio to Niterói.
The headline figure is the time saved. The study estimates a trip from the busy Icaraí district of Niterói to Santos Dumont airport in central Rio would fall from about 75 minutes to roughly 11, a cut of around 85 percent.
For the wider corridor, earlier plans projected the line would serve some 650,000 passengers a day and slash cross-bay commutes that can run to two hours. The numbers explain why the project refuses to die.
Why it keeps stalling, and why now
The history is a catalogue of false starts. Federal money was announced in 2011 and never flowed, a 2023 state tender for feasibility studies was annulled by auditors, and the bay tunnel has stayed on paper for half a century.
The Rio Times reads the new push as part of a bigger play. Rio and Niterói are bidding to host the 2031 Pan-American Games, and a marquee transport project is exactly the kind of legacy promise such bids are built on.
There is a clear parallel with history here. The last great leap in Rio’s metro, Line 4 to the Barra da Tijuca, was delivered for the 2016 Olympics, showing how mega-events can unlock funding that routine planning cannot.
The current study is funded by federal and state money and has a 30-month horizon to map the route, costs and economics. It is meant to give decision-makers a credible basis rather than another shelved blueprint.
The technical challenge is what has always made the line so expensive. Boring a rail tunnel beneath a working bay means contending with marine geology, ship traffic and the environmental state of Guanabara, long one of Brazil’s most polluted waters.
The corridor it would serve is among the most strained in the metropolitan region. Niterói and São Gonçalo together hold well over a million people, most of them funnelled daily onto buses, ferries and the single road bridge into the capital.
For investors, the read-through is caution tempered with interest. Rio state carries real fiscal strain, and a bay tunnel is among the costliest civil-works a city can attempt, so financing structure will decide whether this round is different.
The forward question is whether the Pan-American deadline turns folklore into steel. A confirmed Games host decision would put a clock on a project that has never had one.
Frequently Asked Questions
What is Rio Metro Line 3?
It is a long-planned metro line that would become Rio de Janeiro’s first intercity rail link, connecting the capital to Niterói and São Gonçalo across Guanabara Bay. The route would run through an underwater tunnel and stretch about 50 kilometres with roughly 29 stations.
Has construction started?
No, the project is still at the study stage, with a Coppe/UFRJ team given 30 months to assess the route, costs and viability. It has been promised repeatedly since the 1970s without ever breaking ground.
Why is Rio Metro Line 3 back in the news now?
A new university study published fresh numbers in June 2026, including an estimated 85 percent cut in some cross-bay journey times. The revival is linked to Rio and Niterói’s bid to host the 2031 Pan-American Games, which could unlock funding.
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