It’s been taunting us for several years now.

The half-finished Navy Pier Flyover promises to save thousands of lakefront cyclists and pedestrians the sometimes dangerous — always a hassle — task of navigating two busy intersections and a congested stretch of crumbling sidewalk, in order to get across the Chicago River and, once again be on your way.

After years of planning, construction began in 2014 and was slated to be done by the middle of 2018.

This timeline was on par with the construction timetables of the Golden Gate Bridge and Hancock Building. The Mackinac Bridge was built in little more than three years.

And officials now say that unanticipated design complications have set back construction even further.

The incomplete structure will continue to tease outdoor enthusiasts well into 2019.

The problem: the double-deck bridge that carries traffic over the river on Lake Shore Drive and opens and closes for boats. It’s the centerpiece of the flyover project. And the bridge, built in the 30s, requires more fixes than originally thought.

It is listed as one of the most structurally deficient bridges in Illinois by the American Road & Transportation Builders Association.

Mike Claffey, a spokesman for the Chicago Department of Transportation, couldn’t say exactly why, with foreknowledge of the poor state of the bridge, the extent of necessary repairs weren’t properly anticipated.

And although the delay was just announced, Claffey couldn’t say exactly when project planners realized the completion date would need to be pushed back.

“It would have been nice if these bridge deficiencies had been discovered earlier to keep the project on pace,” said Ron Burke, executive director of the Active Transportation Alliance, an advocacy group for pedestrians and cyclists.

But more central to understanding the considerable length of the project is the issue of piecemeal federal funding that’s covering most of the tab.

“People tend to think ‘How could this possibly take so long?’ and they tend to jump to conclusions about poor planning,” Burke said.

“The reality is that when it comes to funding roads for cars, the federal government has the process down pat, but when it comes to building space for biking and running, it’s a different story,” he said.

“And the city, to their credit, went out and scrambled and was really entrepreneurial and found multiple pots of federal money that ideally would have been released in such a way that construction would have been more seamless. But they weren’t all timed together,” said Burke.

“So the project was going to be really hard to do faster than four years. Even if every dollar had been available at the same time, it sounds like it would have taken at least two years,” Burke said.

So far, construction of the ramp connecting the Flyover to the lakefront trail, beginning at Ohio Street Beach on the north side of the bridge, is partially built. But it doesn’t connect to the bridge deck that spans the river.

The ramp will allow lakefront trail users to bypass Grand Avenue and Illinois Street.

Work on the ramp — otherwise known as phase two of the project — is set to begin by the end of this month and last through 2018.

But runners and cyclists will still be left dodging each other on a congested eight-foot sidewalk that spans the river on the lower level of the east side of the bridge.

Construction to double the width of this sidewalk — also known as stage three of the project — is expected to begin in the middle of 2018 and last about 12 months.

In order to accomplish this, an eight foot surface will be added to the east side of the bridge. Bridge houses bookend this new section of pathway, so workers will tunnel through them.

During construction, pedestrians will be able to cross the river on either the sidewalk that’s traditionally been used, or a lane of the adjacent roadway that will be closed to cars.

By the middle of 2019, the flyover, in all its glory, should be fully usable — although construction on mechanical elements of the bridge will last through the end of the year.

“It’s going to totally be worth the wait. It will carry more people than most roads carry people in cars,” Burke said.

A study conducted five years ago showed that about 100,000 people use the lakefront path on an average weekend day in the summer.

“Probably even more people use it now. And the area around Navy Pier is one of the busiest,” Burke said.

The surface of the flyover will include lanes separating pedestrians and cyclists — a configuration that will be consistent with the entire length of the 18 mile lakefront trail. But lane separation project is well underway and slated for completion by the end of 2018.

In addition to the delay, the original $60 million price tag of the Navy Pier Flyover project is expanding, Claffey said, although he couldn’t provide exact figures.

“We knew from the outset that it was an extremely complex project both to design and construct and that it would be a challenge to fund it,” Claffey said.