In the world of big transportation projects, it’s not unusual for something like, say, the Bay Bridge eastern span or Boston’s Big Dig, to go over budget and take longer than anticipated.

What is somewhat unusual is when, part way through an expensive and complex project, a project is projected to be completed within budget and on schedule.

Yet, that’s the case with the Municipal Transportation Agency’s controversial Central Subway project, which the Federal Transit Administration had faulted for cost-reporting errors and the failed implementation of a cost-control system.

But the city Controller’s Office conducted an audit and concluded that the project had cleaned up its act. The controller predicted that “the project will not exceed its baseline budget and will open to the public as planned.”

The 1.7-mile Muni Metro line will run above ground from the Caltrain station at Fourth and King streets to Bryant Street then underground to Washington Street in Chinatown, with stations at Fourth and Brannan streets, Moscone Center, Union Square and Chinatown. It is budgeted at slightly less that $1.6 billion.

According to the controller’s report, with the scintillating title “The Central Subway Project Cost Reporting Practices Have Improved,” it could come in $64 million under budget, and should be carrying passengers by December 2018 as scheduled, despite being slightly behind schedule now.