Last December, the Colorado Department of Transportation debuted what it dubbed a Peak Period Shoulder Lane — shorthanded as PPSL — constructed along a thirteen-mile stretch of Interstate 70 heading eastbound from Empire to Floyd Hill.

The idea was to ease traffic on Saturdays, Sundays and holidays for people returning to Denver from the mountains along a stretch known to bottleneck, thereby causing delays that could stretch into hours.

Granted, the costs for using the lane seemed likely to put a pinch on the pocketbook. Fees ranged from $3 to $30 for folks who'd set up an ExpressToll account. But drivers who hadn't — like visitors in Colorado to ski or locals who don't travel the route every day — would be hit with an additional processing surcharge that bumped the top charge up to $40.

That was a high potential price for a service that no one seemed sure would actually work to reduce I-70 traffic hell or by how much.

But a funny thing happened on the way to another government boondoggle. Statistics show that the express lane did indeed improve the commute, and so does actual user experience. I traveled along the stretch on Sundays twice in recent weeks following visits to the Western Slope. The first time, I experienced some backups in what are referred to as general-purpose lanes approaching the area where the express lane is located through the tunnel just east of Idaho Springs, but not nearly as severe as in recent years; I lost between thirty and 45 minutes. And this past Sunday, I flew through the area in the regular lanes at speeds close to or above the posted limits — without it costing me an extra dime.

Better yet, the highest prices on the scale never came to pass. Most times, the fees for using the PPSL were between $4 and $6.

The results clearly thrill Megan Castle, communications manager for High Performance Transportation Enterprise, the outfit that worked with CDOT to install the $78 million project — and she's not alone.

"The people in Idaho Springs and the mountain communities in Clear Creek County are extremely happy with this," she says. "It's impacted their frontage roads, which aren't as congested with people getting off the highway, and businesses are having a positive impact. Business is up and people are getting into their communities."

We've included CDOT stats below — but here are some graphics that illustrate the improvement in speeds through the area, using Labor Day weekends in 2012 and 2016 as comparisons. First, a side-by-side look, which shows speeds up from thirty miles per hour or below to free-flowing.

The next graphic offers a color-coded look at speeds in 2012....

...versus 2016:

The number of cars using the express lane during peak periods was around 8 to 10 percent of the overall volume, which was in line with predictions, Castle says.

"We expected more cars to be in the express lane in the summer, since summer traffic overall is higher than winter traffic," she notes, adding, "We're not looking to get everybody into the lane. We want to price it just right — not so high that no one is in there, but not so low that everybody is and it slows down, too."

The lane is unique, Castle points out — "the only one in the country that's based on recreational traffic instead of a regular commuter base."

Anecdotally, Castle says CDOT is hearing that people who previously avoided I-70 during busy weekends may be reconsidering based on lane-related commute-time improvement. "Is there a lot of pent-up demand from people who may not have made that trip into the mountains before, but now they're feeling they can go? We'll have to wait and see."

As for the revenues generated during season one of the lane, those totals won't be in for a while because of lag time from people mailing in fees if they aren't already ExpressToll customers. But Castle isn't waiting to breath a sigh of relief about how things have gone so far. "We're super-happy about it," she allows.

Here are CDOT stats from the express lane's first go-round.

Summary of I-70 Mountain Express Lane’s First Summer Season:

Capacity:

• Throughput increased by 14 percent

• Corridor had 1.06 million vehicles compared to 993,500 in 2015

• Express Lane captured 82,600 vehicles (8 percent of the total vehicles)

• Peak day increased throughput by 4,200 vehicles per hour

Travel Times for Express Lanes:

• Average travel time was 12.1 minutes (59 mph)

• Peak-hour travel speeds stayed above 40 mph and above 30 mph in GP lanes throughout the season

• Fastest: 10.5 minutes (68 mph) on Saturday, July 9; GP lanes 11.5 minutes (62 mph)

• Slowest: 16.1 minutes (44 mph) on Sunday, June 19 (Father’s Day); GP lanes 19.4 minutes (37 mph)

Travel times for General Purpose Lanes:

• Improved by 38 percent

• Peak-Hour Season Average: 14 minutes (51 mph)

• Fastest: 10.7 minutes (66 mph) on Saturday, Aug. 27

• Slowest: 21.1 minutes (34 mph) on Sunday, June 26

• 2013-2015 Peak-Hour Season Average: 22.4 minutes (32 mph)

• Slowest: 80.4 minutes (9 mph)

• Fastest: 11.9 minutes (60 mph)

Safety and Incidents:

• 14 total corridor incidents:

• 4 in Express Lane; 3 straddled Express Lane and GP lanes; and 7 in GP lanes

• Averaged 18 minutes between an incident reported and cleared

• Time to clear corridor back-ups substantially improved

Toll Rates typically $4 to $6

Additional Results and Findings:

• In a worst-day comparison between 2015 and 2016, travel times on the Mountain Express Lane corridor improved by 21 minutes.

• Alleviated congestion on Frontage Road and improved travel time between Georgetown and US 40.

• Summer season throughput increased.

• When compared to winter, the Express Lane use was lower on Saturday, but much higher on Sunday.

Comparing Labor Day traffic from 2012 (pre-construction) to 2016:

• 2012: 40,500 vehicles per day with speeds consistently below 20 mph

• 2016: 46,300 vehicles per day with speeds that were predominantly above 45 mph and occasionally dipped to 30 mph

