State transportation officials are about to put a congestion reduction strategy on Interstate 25 south of Denver into high gear, with plans this month to expand a precision-driven ramp signaling system to traffic-choked connections at I-225, E-470 and C-470.
Colorado Department of Transportation Smart 25 Project Manager Zach Miller said adding the big interchanges on I-25 in Douglas and Arapahoe counties to the effort to manage the flow of traffic through the Denver Tech Center is “critical to the system.”
“When there is an incident on the highway, the system needs to be able to control these three large contributors to the mainline,” Miller said.
And an incident on I-25, which sees upwards of 250,000 vehicles a day, can send motorists into paroxysms of frustration as taillights illuminate and forward progress gets stymied. It’s why CDOT put in place the Smart 25 Managed Motorways Pilot Program last spring, hoping to use an array of roadbed sensors and computer algorithms to control motorists’ access to I-25 with fraction-of-a-second precision never before seen in Colorado.
CDOT borrowed the idea of “coordinated ramp metering” from Australia, where a decade ago Melbourne implemented it on a stretch of the M1 through the city. The results were dramatic: The number of vehicles getting through on the highway increased by 25% during peak commuting periods, travel speeds improved 35% to 60% during peaks and crashes went down by 20% to 50%.
Miller said CDOT won’t know just how well real-time ramp metering is working on I-25 until all the data is in and analyzed, which he expects to be completed this summer.
“The algorithm was slowly increased until full activation was reached in late December,” he said. “Therefore, the current condition has been running for only a few weeks.”
For most of last year, CDOT was in what it called a “soft launch” phase of the system, in which sensors on a 14-mile stretch of northbound I-25 between University Boulevard in Denver and Ridgegate Parkway in Lone Tree, plus a dozen “sensing pucks” at each of 15 ramps in the study area, feed traffic flow data to computers.
Those computers, in turn, adjust the timing of a ramp signal’s red and green lights in real-time every 20 seconds or so — sometimes by as little as a tenth of a second — to keep things moving as smoothly as possible. But the real test of the system won’t come until the meters on the ramps connecting I-25 to I-225 and the 470 beltway around Denver are integrated into the network.
“The next step will be to monitor and make adjustments to the algorithm once the freeway-to-freeway ramp meters are turned on,” Miller said. “We expect changes to how the system works when the freeway-to-freeway ramps are activated.”
If results prove hopeful this summer, CDOT could add southbound I-25 to the system and make it a permanent feature of the highway.
Jeremy Hanak, director of public works for Greenwood Village, said he hasn’t noticed congestion relief on I-25 through his city yet. But he said cars trying to get on the highway are causing some crowding on the ramps.
“We are seeing the ramps back up more frequently as the pilot project continues to adjust the timings,” he said.
One issue, Hanak said, is that drivers aren’t using the ramps as efficiently as they could, with a “lack of utilization of the third lane that was created at a few of the interchanges.” Miller, with CDOT, said the right shoulder on the ramps at Lincoln Avenue, as well as at East Dry Creek and Arapahoe roads, can be used when the ramp meter is active.
But drivers don’t always catch on, despite signs informing them of the situation.
“It has taken a while for motorists to get used to this new condition,” Miller said.
CDOT has been responsive to concerns from Centennial, where the primary concern is that traffic stopped on the ramps will spill onto that city’s streets, said Melanie Ward, strategic adviser for transportation and mobility in Centennial.
“CDOT shared if the traffic backed up onto Centennial’s arterials, the ramp meters would turn off, allowing cars to flow onto the interstate,” she said.
