CHICAGO (CBS) — The Navy Pier Flyover will close temporarily starting Tuesday, as crews work to complete the second of three phases for the long-awaited overpass along Lake Shore Drive.

The closure will last through the end of September as the first two phases of the project are connected.

The Chicago Department of Transportation said cyclists and pedestrians will be directed to use the old Lakefront Trail route along Lower Lake Shore Drive, crossing Illinois Street and Grand Avenue.

The long-awaited Navy Pier Flyover is far behind schedule. Work began in 2014, and originally was scheduled to be finished by spring 2018, but the start of construction was delayed two years, due to unexpected engineering challenges, and now is set to be finished at the end of this year.

The bypass is designed to reduce congestion on the popular Lakefront Trail as it crosses the Chicago River just south of Navy Pier.

It ultimately will eliminate a dangerous bottleneck at street level near Navy Pier, where cyclists and pedestrians are forced to crowd on a narrow sidewalk to cross Illinois Street and Grand Avenue along Lower Lake Shore Drive.

The first section of the $64 million flyover project was completed last December, running from Ohio Street Beach to Illinois Street, and the second phase is almost done. A temporary bridge will connect the flyover to the east sidewalk on the Lake Shore Drive Bridge over the Ogden Slip.

Once the Navy Pier Flyover reopens in September, CDOT also will open a new ramp from the flyover east to Navy Pier along Illinois Street.

The final phase of the project will create a wider trail on the east side of the Lake Shore Drive Bridge over the Chicago River to the north end of DuSable Harbor. The third phase is scheduled to be completed at the end of this year.

Once it’s finished, the project will create a 16-foot wide lakefront bridge for pedestrians and cyclists from just south of the Chicago River to Ohio Street Beach, running parallel to Lake Shore Drive.