The fast-growing Denver area bet big in the last two decades on giant, galvanizing transportation projects that still win praise from regional planners but have left many areas susceptible to serious delays. By most accounts, the region faces future demands that, if left unresolved, could drown the highway system with longer periods of unrelenting traffic.

A recent regional congestion report predicts that in coming decades, the volume of vehicles may grow so much that “the period from 2 to 4 p.m. in 2040 (will) have as much traffic as from 4 to 6 p.m. today.” Meanwhile, that later period will worsen.

MAP: Denver transportation projects 1998-2018

And the normal midday lull? By 2040, that period could seem as bad as today’s morning rush hour, according to the October annual congestion report from the Denver Regional Council of Governments.

An added risk, DRCOG’s analysts say, is that early-afternoon crashes, if not cleared more quickly than they are now, will cause backups that snowball for hours, making the evening commute even more miserable.

Denver-area transportation planners largely have kept up with the region’s growth of the past 20 years and are preparing for more to come, The Denver Post found in a review of planning documents going back to the late 1990s and dozens of major projects that have unfolded. The Post also interviewed current and former metro planning officials, advocates and Colorado Department of Transportation leaders.

Those projects over two decades totaled more than $11 billion and were dominated by big-ticket items that observers agree have improved commutes for many, including the massive T-REX project on southeast Interstates 25 and 225 as well as the rapid expansion of the light-rail and commuter-rail system.

But well-intentioned plans drawn up years ago for other traffic-choked corridors — such as I-25 through the north metro area — have been hamstrung by harsh financial realities that, as in most of the country, have kept badly needed projects from launching.

The same recurring budget pressures, as well as the long-standing lack of political will to buck anti-tax sentiment and raise the money needed at the state and federal levels, could restrain the region for decades to come.

And so planners are faced with the prospect of spending most of the dwindling money available to maintain a system that can grind to a halt anytime there’s a traffic accident or mildly inclement weather.

After big projects such as T-REX, “the challenge is that a lot of these improvements in a typical state would have fixed the problem,” said Shailen Bhatt, CDOT’s executive director since February. “The challenge is that Colorado is not a typical state. We’re a growth state, and we’ve been growing and we’re going to continue to grow.”

DRCOG, the main planning group for 56 local governments from Castle Rock to Longmont, this year adopted its latest 25-year transportation plan.

Its planning region has grown from about 2.2 million people in 1996 to an estimated 3.1 million now, an increase of about 45 percent.

By 2040, its projections estimate, the same area will be home to 4.3 million — an additional 38 percent increase — and a continuation of the 4,000 to 5,000 monthly net influx into metro Denver in recent years.

Douglas Rex, DRCOG’s transportation planning director, compares the coming growth to absorbing the population of the Oklahoma City area.

In that same 25-year period, the plan estimates the state and region will be able to gather enough money from all sources to pay for $106 billion of road and transit projects.

But the metro area needs $153 billion in projects to keep up with all maintenance needs and deliver congestion relief, DRCOG’s planners say.

Commutes getting worse

In metro Denver, national studies show that commutes are getting worse. That’s especially true in some places — such as in the southwest and northern suburbs — where well-vetted plans drawn up by CDOT and others have collected dust because of local fights or funding shortfalls.

“My commute is long, and traffic is terrible,” said Mike Lloyd, a software engineer who fights traffic along West 120th Avenue in Thornton to catch an express bus to Union Station, a trip that sometimes takes an hour or more. “I-25 is almost always at a crawl, north and south; 120th is immensely congested. I wish they would widen it.”

Advocates have pushed for a north I-25 version of T-REX, the nearly $1.7 billion multiyear makeover of I-25 and I-225, finished in 2006, that installed new traffic lanes along 17 miles and laid new light-rail tracks to smooth the commute — or at least improve it most days — from the southeast suburbs through central Denver.

Other giant projects have included two toll roads — E-470 and the Northwest Parkway — that suburban cities and counties pursued through farms and pastures by forming separate toll authorities to finish most of the metro area beltway, at a cost of more than $2 billion in today’s dollars.

And the Regional Transportation District is nearing the finish line on most pieces of the $5.3 billion-and-counting FasTracks rail system, offering more metro commuters an exit from the freeway grind.

But rather than new projects scaled as large as T-REX, which required voter approval for borrowing, the best hope state transportation officials say they can offer rests on two things: new technology and managed toll lanes.

Developing technologies are expected to make more cars less prone to gridlock-causing accidents and are producing new systems that hold promise for reducing road congestion.

In the next year or so, CDOT plans to launch a pilot on a portion of I-25, from Broadway to Ridgegate Parkway in Douglas County, by upgrading the northbound on-ramps’ metering system to a dynamic, computerized version. Drivers may wait longer to get on the highway at times, Bhatt says, but CDOT projects that the new system could improve I-25’s traffic flow as much as 25 percent.

CDOT already is embracing managed toll lanes, which carry the benefit of helping to offset construction costs, on some congested corridors.

Sometimes shoehorned into highway shoulders, those lanes are free for buses and carpools but charge varying tolls for single-occupant cars. They appeal to drivers who are desperate enough to pay to escape the snarl, and CDOT says they will ease congestion across all lanes.

Such lanes just opened along U.S. 36 and on the shoulder of eastbound Interstate 70 along a 13-mile mountain stretch for return ski traffic. They also are at the center of coming plans to overhaul I-70 through northeast Denver and a long-delayed upgrade of the most congested parts of C-470 that will start next summer.

A new set on I-25 from U.S. 36 to 120th, connecting with existing toll lanes to the south, soon may quicken the bus portion of Lloyd’s commute.

CDOT is making plans to extend managed lanes even farther north through the suburbs, rather than calling for a large-scale widening that many local leaders and commuters prefer.

Some transportation experts, though, say additional free-access lanes are more likely to fill up quickly by inducing drivers to switch back to peak times.

But Lloyd says he is holding out for RTD’s under-construction North Metro Rail Line, which could jettison the unpredictable I-25 from his commute by 2018.

49 hours in traffic

The average commuter in the Denver metro area spent 49 hours sitting in traffic last year, according to the Texas Transportation Institute’s Urban Mobility Scorecard. Denver ranked 19th among U.S. metro areas.

The annual report has improved its estimates in recent years by incorporating real-time speed data from a company called INRIX that is tracked from some drivers’ Global Positioning System-enabled phones and devices.

The delay measurement is lower than the 52 hours that the institute estimates Denver-area drivers spent delayed by traffic in 2005, when the T-REX project was nearing its end. But after several years of reduced delays following that project’s completion — and during the Great Recession — area commuters’ delays have been inching upward again.

Twenty years ago, according to the institute’s revised estimates, Denver-area drivers were delayed only 31 hours by traffic, ranking the region 40th for that year.

This year’s national report ranked I-25 northbound between Colorado Boulevard and 84th Avenue as the 51st-worst-congested corridor last year, while the southbound side was ranked 147th. In another ranking by the American Highway Users Alliance, I-25 between Santa Fe Drive and Logan Street — a stretch near recent construction projects — was the 35th-worst bottleneck this year.

Even in the T-REX zone in the south suburbs, where I-25 now has five continuous lanes in each direction, traffic levels cause daily frustration for some drivers.

“My commute is only going to get worse, thanks to the construction around my office (in the Denver Tech Center) and now my home,” said Brian Soucie, who lives off of Dry Creek Road and works for a financial investment firm. “The intersections and routes that I take are not capable of handling the amount of traffic that has been generated in the area.”

Transportation planners, CDOT officials and some observers say freeways and some arterial streets through older parts of the Denver area have little room left for expansion.

And they point out that Denver’s congestion rankings are comparable to its relative size as a metro area. In other words, traffic is a symptom of its success in attracting jobs and residents.

The average commute in most of the metro region, excluding Boulder, took about 27 minutes in 2013, according to U.S. Census estimates. That’s slightly above the national average of 26 minutes.

In the Texas Transportation Institute’s traffic-delay estimates, Denver ranks better than comparably sized — but notoriously snarled — Austin, Texas; Seattle; and Portland, Ore., while cities such as Chicago (61 hours of delay a year) and top-ranked Washington, D.C. (82 hours), have congestion that makes Denver traffic seem almost quaint.

“Our level of congestion, it is an issue,” said Rex, DRCOG’s transportation planning director. “But it seems to be on par with what our population is. Our economy is booming compared to many parts of the country, but we certainly can’t rest on our laurels.”

High marks from experts

The coming pace of the metro area’s growth initially was underestimated by DRCOG in the late-1990s, but the organization’s projections — by nature fraught with uncertainty — get high marks from transportation experts.

“DRCOG does a great job at projecting traffic levels,” said Bruce N. Janson, a civil engineering professor at the University of Colorado Denver. “They’re one of the most progressive metropolitan planning organizations in the country with regard to their traffic forecasting methodology.”

But with the traffic trouble spots known well, it was up to state and local officials to prioritize projects, given limited funding.

That led to the huge T-REX project still excluding several miles of I-25 that was in need of a fix, from Broadway to the Sixth Avenue Freeway. Only recently was CDOT able to clear the bottleneck created there by creating a fourth continuous lane to link to the end of the T-REX zone.

Other projects approached piecemeal over a decade or two included an extension of Interstate 270 from Interstate 76 to I-25, the complex remodeling of the “Mousetrap” interchange of I-25 and I-70, and widening of U.S. 285 into the foothills.

But some critics long have questioned transportation spending priorities, especially the FasTracks plan.

Randal O’Toole, a senior fellow at the libertarian Cato Institute who also is connected with Denver’s Independence Institute, says the money could have been put to better uses, and at lower cost.

“Instead of building six new rail lines, they could’ve built 50 bus rapid transit lines around the region and served a lot more people than the six rail lines are ever going to do,” said O’Toole, who lives in Oregon.

He also suggests that continuing funding gaps for transportation projects are due to politicians wanting glitzy projects to show off instead of what he considers more common-sense solutions.

O’Toole supports a recent Reason Foundation report on Denver’s congestion problems that advocates for a $52 billion plan that relies heavily on toll lanes added along most freeways and at some major surface street intersections as a form of congestion pricing. The plan, which would be much less costly than DRCOG’s 25-year plan, also incorporates a heavy expansion of bus service.

Repeated road expansion

But Bill Vidal, who was a CDOT chief in the 1990s, said the development of the rail system was a credit to good planning that incorporated new thinking beyond repeated road expansion, instead focusing on how to move people better. He later served as director of DRCOG and then as Denver’s public works director, retiring after a stint as interim mayor in 2011.

“As we started carrying big-city traffic, neighborhoods were affected by that traffic,” said Vidal. “So people are noticing that just driving a car may not be a good idea — even if they might be driving a car 100 percent of the time themselves.”

The transit lines also have been credited with spurring development near some stations, and Rex and others say they have helped people with more options to avoid driving in traffic than they had 20 years ago.

“Cities with congestion that do mobility well don’t rely on a single mode to meet their transportation needs,” Crissy Fanganello, Denver’s director of transportation, wrote in an e-mail. “They have robust transit system (bus and rail), they have bike facilities, people walk and in recent years new services have emerged,” such as Uber and bike-sharing.

Last year, RTD recorded nearly 104 million boardings, including 26.3 million light-rail passengers. In 1993, before the first light-rail line opened, its system ridership — entirely on buses — was 61.4 million.

Amid rising costs for 2004’s voter-approved FasTracks plan, originally set at $4.7 billion, RTD has put some components on hold, including most of the northwest rail line.

But next year will feature the opening of several lines that are nearing completion. Existing light-rail lines in central Denver and to the southwest, southeast and west will be joined by commuter-rail lines from Union Station to Wheat Ridge, Westminster and Denver International Airport, along with the completion of the I-225 light-rail line. And on Jan. 3, the Flatiron Flyer bus rapid-transit corridor will open on U.S. 36, using the newly constructed toll lanes.

For airport travel or suburb-to-suburb commutes, E-470 has become a popular alternative to freeways through Denver, with toll transactions increasing 71 percent from 2003, when the final section opened, through last year.

But the prospect of further large improvements to absorb more metro growth is daunting to planners, local officials and commuters alike.

There’s also the added uncertainty about how emerging social trends, including the effect of the coming baby boomers’ mass retirements and millennials’ preference for getting out of cars, will affect road congestion in coming decades.

Transportation frustrations — which extend to other parts of the state, too — are at the heart of varying efforts to find ways to raise yet another infusion of money for projects, from Gov. John Hicklooper’s office to the General Assembly to lobbying groups that have formed to push for additional lanes on I-25 even farther north, through Fort Collins. Without more money, CDOT says it can’t get that job done until 2070.

But taxing and spending restrictions under the Taxpayer’s Bill of Rights have long been a major hurdle, making borrowing a more attractive option in the past to raise infusions of cash for projects.

More recently, the state has raised vehicle-registration fees to pay for the FASTER program.

But it has been 22 years since both Colorado and the federal government last raised their gas taxes, a long-standing major source of transportation funding that has dwindled. Those taxes are a combined 40.4 cents per gallon.

Without new funding, CDOT says its current annual $800 million funding gap — on a $1.3 billion budget for its statewide mission — could grow to $1 billion in coming years.

Jon Murray: 303-954-1405, jmurray@denverpost.com or @JonMurray

How we commute

A U.S. census report on commuting for 2013 estimated how residents in the Denver area (excluding Boulder) traveled to work and how long it took, on average:

• By car: 75.4 percent (26 minutes).

• By carpool: 8.9 percent (29 minutes).

• By public transit: 4.4 percent (47 minutes). Surveys by the Downtown Denver Partnership, while not scientific, suggest that far more downtown workers — roughly 40 percent in the 2015 survey — commute most days using public transit.

• Another way: 11.3 percent (no time given).

Things you can do

Avoiding traffic can be tough, but there are ways to reduce the time stuck in gridlock:

• Use Google Maps, Waze or other mapping apps for your phone that collect real-time information from other drivers with phones to recommend ways around bottlenecks, accidents and other tie-ups.

• If you drive to work, see if transit might offer an appealing alternative.

• If you live within a few miles of work, consider commuting, on warmer days, by bike or on foot.

• Check the Denver Regional Council of Governments’ MyWaytoGo.org website. Enter your start point and destination, adjust the time for your commute and see comparisons of options, including the best bus or train routes and carpools registered along your route.

• Explore changes that might reduce time spent in traffic, including shifting your workday earlier or later, or working from home some days.