By 2015, the agency and the union say RTD's hiring and retention problems had taken hold. Starting wages were stuck at about $15 an hour at the time, and would top at around $17 an hour until the five-year deal ended in early 2018. In roughly that same span, per capita personal income rose from $51,804 to $59,660.

Such are the pitfalls when negotiating a long-term deal, said RTD spokeswoman Pauletta Tonilas.

"None of us can look into a crystal ball and see what the future holds,” Tonilas said.

In the intervening years, RTD has lost a lot of drivers — even as new train lines opened. That’s left it with a big gap between the workforce it needs and its current headcount, which newer agreements haven’t closed.

A new contract in 2018 immediately boosted pay by 8 percent — starting wages are nearly $20 an hour now. And it codified a number of protections meant to improve workplace conditions, like limiting overtime, incentives for split shifts and guaranteed bathroom breaks. The problem, Jones said, is that schedules are still too tight for drivers to take them.

“RTD scheduling puts operators in a position where they have to almost be apologetic for being a human being,” Jones said. “You know, ‘Sorry, I need to go use the restroom. I know it'll make you late. You might miss a connection.’ And most operators don't do that to the passengers.”

RTD spokeswoman Tonilas said it's up to operators to take their breaks.

“It is built into the schedule,” she said. “And while some of those schedules are tight, no operator has been reprimanded for taking a restroom break.”

While that is true, said ATU 1001 President Julio Rivera, drivers have been disciplined for finding more creative, and public, ways to relieve themselves when restrooms aren’t available.

“It’s not common,” Rivera said. “But it’s common enough that it’s becoming an issue.”

In a new report, RTD senior staff said the agency has hired nearly a thousand train and bus operators since January 2017 — but nearly just as many have left their jobs. Jones said working conditions are the top reason for employee turnover.

The proposal to cut service could immediately help with work conditions, by drastically reducing mandated overtime.

“Our employees are our most valued commodity, and their quality of life means a lot to us,” Tonilas said.

RTD is not alone in driver shortages.

Ben Fried, spokesman for New York-based Transit Center, a research and advocacy group, said shortages are hampering service in major metro areas like San Francisco, Minneapolis-St. Paul, Omaha and St. Louis.

“But what Denver is doing is really a step beyond what we've seen in other places,” he said. “They are basically admitting that they don't have the workforce to operate their schedules.”

Addressing the shortages and restoring service should be RTD’s top priority, Fried said. He suggested it raise more revenue to increase service throughout the day, requiring fewer burdensome split-shifts for drivers.

“If you provide that sort of constant all-day frequent service, that's not just better for bus drivers,” he said. “It's better for riders too.”

However, because of Colorado’s limits on tax increases, RTD would likely need voter approval to raise any significant amount of new revenue. (Fares comprise less than 15 percent of revenue.) And because RTD hasn’t yet finished its promised train line to Boulder and Longmont, even though it’s still collecting taxes for it, any more funding asks could be politically challenging.

RTD is embarking on a two-year process to “reimagine” what it does, and where. Tonilas said that should bring the agency’s long-term priorities and goals into focus.

“It is going to take more money for all of us to be able to move people around the way they want and need to move around,” she said. “We don't have all the resources that we need here at RTD. And however that looks as a region, it's going to be up to all of us to succeed together.”