Easing the notorious rush-hour gridlock on Interstate 25 south of Denver will require controlling thousands of motorists’ access to the highway with fraction-of-a-second precision never before seen in Colorado.
It’s why in the next few weeks, state transportation officials will launch the Smart 25 Managed Motorways Pilot Program, using what’s called “coordinated ramp metering” on a 14-mile stretch of northbound I-25 between University Boulevard in Denver and Ridgegate Parkway in Lone Tree.
Many entrance ramps on metro Denver highways have traffic lights to control traffic flow but they aren’t programmed to respond to real-time conditions. By making constant and minute changes to the length of time cars wait on entrance ramps before merging onto the highway, traffic engineers believe slowdowns and logjams can be greatly reduced — or avoided altogether.
The proof, according to Colorado Department of Transportation Smart 25 Project Manager Zach Miller, resides nearly 8,800 miles away in Melbourne, Australia.
“Australia has figured out how to use algorithms to resolve complex traffic problems to prevent congestion,” Miller said. “I am hopeful this technique can be beneficial to CDOT as well.”
What Australia’s second-biggest city found after implementing its coordinated ramp metering program on a stretch of the M1 freeway a decade ago is impressive: The number of vehicles getting through increased by 25% during peak commuting periods, travel speeds improved 35% to 60% during peaks and crashes went down by 20% to 50%.
“We can’t control what the drivers do, but we can control the environment in which they make these decisions,” said Matt Hall, a manager with the Victoria Department of Transport.
And that environment is one of extreme precision: Traffic conditions on the roadway are constantly monitored by sensors, which send data to algorithm-chewing computers. The length of time the green or red light on an entrance ramp illuminates is adjusted every 20 seconds.
“It slowly pushes out red time as needed,” said John Gaffney, strategic advisor to the Victoria Department of Transport. “And if one area is struggling, we share the pain across the system.”
Sometimes that means adding just a tenth of a second to motorists’ wait time, Gaffney said, but manipulating wait times on numerous ramps across miles of highway helps to fill in what empty spaces there are on the highway to keep traffic moving smoothly. It only takes two additional vehicles per lane mile to bog it all down, he said.
The stretch of I-25 through the Denver Tech Center sees upwards of 250,000 vehicles a day on average, CDOT data shows. Melanie Ward, Centennial’s strategic adviser for transportation and mobility, said there has been no shortage of complaints from city residents about I-25.
“We hear from our residents all the time that traffic congestion is the biggest concern,” she said.
She welcomes CDOT’s Smart 25 pilot program as a potential solution to congestion — and possibly helping cut down on the metro area’s ozone alert days — but she worries that extended red ramp lights could mean backups on connecting streets.
“We want to make sure we’re not seeing I-25 improvements at the expense of the local roads,” Ward said.
In Melbourne, Gaffney said, that hasn’t been a problem. If a ramp starts to become overloaded, cars will be released while the system transfers wait times somewhere up the road to compensate.
“You have to have all the ramps looking at the system,” he said.
Both Hall and Gaffney said Colorado is on the “leading edge” in putting in place a coordinated ramp metering system. Utah, Georgia, North Carolina and Tennessee, among other states, have explored using it but I-25 already has much of the infrastructure needed in place.
That includes the sensors on the highway and a dozen “sensing pucks” at each of the 18 ramps involved in the study, Miller said. The first three months of the pilot, which could start as soon as the end of June, will be spent collecting data.
The next two months will be a “soft launch” of the program, followed by four months of full operation. Miller said CDOT is spending $5 million on the pilot program, and will be able to assess next year whether it’s something to implement on a permanent basis.
“This corridor was completely refreshed 15 years ago,” Miller said, referring to the additional lanes built on I-25 and I-225 in 2006 as part of the $800 million T-REX project. “However, most of the improved capacity gains have been lost due to increased demands.”
Jeremy Hanak, public works director for Greenwood Village, would just like the worst of the rush hour through his city to grow no longer or more intense than it is.
“If you get a coordinated traffic signal system, you can increase efficiency,” Hanak said. “Hopefully, you can stop yourself from going from a one-hour peak period to a two-hour peak period.”