Since debuting at the Apple Valley zoo in an era when sleek, futuristic trains were springing up at zoos across the country, the monorail was plagued by low ridership and financial shortfalls. In the early 1980s, it came close to being repossessed or even sold for scrap. In recent years, it had been more quietly losing money, until finally, this fall, the zoo pulled the plug.

“It was an outdated system that had reached the end of its useful life,” said zoo spokeswoman Kelly Lessard. There were “no viable or affordable options to replace [it]. … The manufacturer has long been out of business.”

Commissioning new trains to run on existing track, she said, would have cost “in excess of $40 million, and we determined this would not be the best use of future capital dollars since monorail ridership had declined over the years to below 15 percent of the zoo’s total annual attendance.”

Originally, the zoo intended the monorail to be a transit device to carry people to the outer edges of the property, aimed at “young families who aren’t interested in walking six miles to see a musk ox,” Director Lee Ehmke once confided. But there was never any station to disembark from, just a long slow loop.

The monorail always struggled to attract enough riders, and right up to its last days of service around Labor Day, online comments from zoogoers were often scathing, characterizing the monorail as both “lame” and “pricey.”

“I don’t think it provided any benefit, to be honest,” said Tim Trudell, a travel blogger from Omaha who has visited many zoos and commented on Minnesota’s online. “It cost extra to ride it. … It took you away from the attractions. I think you’re lucky if you saw animals during the ride. If you did, you couldn’t spend time looking at them, as the monorail made its rounds.”

The transport system was built with an $8.4 million loan from investors — equivalent to $33 million in today’s dollars. It made a profit in its early years, but just a sliver of what was needed to pay back the debt. It felt into default and had to be rescued financially.

As the monorail aged and caused more trouble mechanically, parts to repair it grew harder to find. Yet it did have its fans, given the zoo’s huge size — 500 acres — and the difficulty of navigating young children around a long loop on foot, especially in nasty weather.

“For certain purposes it’s actually a great thing to have,” said Scott Richardson, a Canadian high school teacher and superfan of zoos who takes part in a global online community called ZooChat. “You get an overview of the zoo, and then can choose what to see on foot. For hard-core fans, it’s a positive thing.”

But a zoo should be seen on foot, he added. “It’s a better way. And clearly from online chats with your own zoo director and others, after 30, 35 years they are falling apart and are expensive to keep up.”

As Minnesota Zoo attendance has soared, monorail use just kept sliding, from 185,814 in fiscal year 2009 to 152,153 in the most recent year, according to Lessard.

Annual operating losses ranged from $76,500 to nearly $123,000 from 2009 through 2011. The zoo concluded that it would have needed 40,000 more riders just to break even, a 26 percent increase.

When the state of Minnesota offered the monorail at auction on a website, there weren’t a lot of takers.

“One car from one train was sold to a private entity,” Lessard said. “That car has been removed from zoo property. The remaining 17 cars from the three trains are at the zoo.”

Not all zoos are giving up on their monorails. The zoo in Dallas, for one, has decided to keep its trains on track.

“We’re currently in the planning process to replace our monorail,” said Laurie Holloway, director of communications and social media. “It’s very popular with our guests, and since we’re the biggest zoo in Texas at 106 acres, it’s a great way to cover a lot of ground here.”

Minnesota’s Ehmke, a celebrated exhibit designer, hopes that a new master plan for a much larger Minnesota Zoo will create a willingness to walk farther, with a much livelier scene all around, than the zoo has provided since it opened in 1978. He also has spoken of alternate means of transport where needed.