(Bloomberg) -- Colombian President Gustavo Petro’s proposed modifications to the Bogota metro would cost the nation as much as 15 trillion pesos ($3.3 billion) extra, according to a government official. 

Since he was mayor of Bogota, Petro has argued that the system should be underground to reduce the impact on the capital, Transport Minister Guillermo Reyes told Blu Radio. 

The contract of more than $4 billion for the construction of the capital’s first metro line was awarded in 2019 by then-mayor Enrique Penalosa, who succeeded Petro. Penalosa favored an overground system, which is now in the early stages of construction. 

Authorities are analyzing changes which include having part of the system run underground as well as adding an additional 3.9 kilometers to it, Reyes said. The additional funds would come from the nation’s budget, not from the city, and would prolong the time of construction by as much as five years, he added. 

The consortium met with Petro and Bogota mayor Claudia Lopez Wednesday to present five alternatives. 

Of these, they recommend building the additional 3.9 km underground segment, for reasons of “technical and legal viability”, Lopez told reporters. The consortium is advising against Petro’s proposals.  

The group of companies building Bogota’s subway include China Harbor Engineering Co., Xi’An Metro Co. and Canada-based plane and train manufacturer Bombardier Inc.

--With assistance from Oscar Medina.

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