The Sixth Street Viaduct replacement is the largest bridge project in the city’s history, and it was always expected to be complicated. It’s not a complete surprise then that the contractor now estimates work will be finished in early 2022—not late 2020.

“The projected construction completion date is now March 2022,” according to a Bureau of Engineering report to the Board of Public Works scheduled to be presented on Friday.

In a statement, an engineering bureau spokesperson attributes the delays to “construction challenges,” including the installation of temporary “shoring and falsework” to support the bridge while under construction.

The delays have caused a budget increase, pushing the price tag for the project from $482 million to $488 million. That money was allocated to the project in the city’s annual budget this year, according to the engineering bureau.

The iconic old viaduct was demolished in 2016 after concerns that it was exceptionally vulnerable to collapse in an earthquake. The new bridge was initially projected to open this year. That date was later pushed to 2020.

Whenever it’s finished, the new bridge, designed by architect Michael Maltzan, will connect Boyle Heights and the Arts District and cross over a new public art plaza and park slated to be built underneath the span.

Correction: An earlier version of this story attributed the delay to coordination with the railroads operating the tracks over which the bridge is being built. An engineering bureau staffer initially attributed the delays, in part, to the railroads. But a department spokesperson later said that they were not a factor in the extended timeline.