Editor's note: This post is the first in a series about traffic in Denver.
Many of the traffic signals in Denver seem so long that drivers may be tempted to time them with an hourglass. And Michael Finochio, traffic engineering manager for Denver Public Works, acknowledges that signal time lag has lengthened over the past ten to twenty years in many locations in response to an increase in volume.
Once upon a time, sixty-second signal lengths were common even on highly traveled north-south and east-west corridors, and there are still plenty at less-busy intersections that time out at ninety seconds. But, Finochio says, "because of Denver's rapid growth, the signals on most of our major arterials" — he offers Sheridan Boulevard, Federal Boulevard and Colorado Boulevard as examples — "are currently going on two-minute cycles."
Finochio adds that traffic engineers will sometimes push signals like these beyond the two-minute mark depending on conditions. But thus far, there's just one where this barrier is regularly breached: Speer and Wewatta, near the Pepsi Center, as seen in the image at the top of this post.
"There are a lot of pedestrians who cross Speer," Finochio notes, "and it's a really big roadway — so when cars turn out into Wewatta, we don't want them driving into people crossing. So we needed to give it enough time for pedestrians to cross and people to turn out."
In the end, he adds, "my team settled on 150 seconds," or two and a half minutes.
No one's expecting the signal at Speer and Wewatta to hold the 150-second distinction for long. In many parts of metro Denver, Finochio acknowledges, "we don't have the roadway capacity for the number of vehicles demanding the use — and drivers see that. During the a.m. and p.m. peak rush hour, things slow down, and if something happens, it will not recover until that period is over."
Finochio and other DPW personnel monitor traffic using cameras placed throughout the system, and when an accident, a water-main break or other unexpected occurrence takes place, he says, "we have contingency plans." If there's a shutdown on Sixth Avenue because of a lane closure for construction, for instance, "we know cars are going to go on Federal, Colfax and Sheridan, and we can run different timing plans. Typically what we're doing is increasing the cycle length to give more time to the major arterial."
Making this choice has a ripple effect, he concedes: "There's going to be an impact on side streets, and pedestrians will have to wait longer. But it's much better to move as much volume as we can on Federal than to have drivers wait for a really long time. With cycle lengths of more than two minutes, they can get impatient and start to take risks by turning out into the flow of traffic, and we want to avoid that."
One way of alleviating this kind of stress is to synchronize the lights so that the majority of vehicles can move steadily and safely instead of constantly stopping and starting.
According to Finochio, "We usually time signals to the speed limits and then adjust according to the real volume that's out there. That's our baseline, and in a perfect world, you should be able to hit every green light if you're going the speed limit — and you can count down the seven seconds until you hit the next one."
This ideal is easier to attain on one-way portions of streets such as Broadway, long the gold standard for signal-synching in Denver, than those with traffic flowing in either direction. For the latter, Finochio allows, "it gets a little more complicated — and a lot depends on the cross-road, too. If you're going on Colfax, the progression will be set. But if you hit a major north-south street like Colorado Boulevard that's going to have a higher volume of traffic than Colfax, we're probably going to set the progression at Colorado Boulevard and not Colfax. But that could change. If the next study we do shows Colfax has more volume than Colorado Boulevard, we'll switch it."
Denver Public Works analyzes traffic patterns every three to five years, on average, and sometimes more often depending on the conditions — and tweaks can be made on the fly. In general, though, Finochio says drivers who stick to the posted limits should have the most luck, and if they get stopped by a signal, he discourages them from racing away the instant the light turns green in an effort to avoid missing all the rest along a route.
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"Drivers should get back into progression when the light goes green," he maintains. "That’s how it works on most major arterials in Denver. For example, if you are on 13th Avenue heading west and you got stopped by one red light, you should get green lights for the most part after that if you drive the speed limit — but you could get a red when coming across another major arterial such as Downing or Colorado. Broadway out of downtown should also operate this way for the most part. Speer Boulevard coming into downtown from I-25 should operate that way as well."
Still, these rules of the road have their limits, particularly considering the sheer number of people trying to get from one place to another these days. That's why the administration of Denver Mayor Michael Hancock introduced a new mobility plan last year. Among its goals is to increase the number of commuters walking, biking or taking public transit to 30 percent by the year 2030.
In the meantime, there's only so much Finochio and company can do to keep Denver moving. "We're faced with an over-capacity issue," Finochio says, "and it isn't going to be solved through signal length."
Whether they last for two and a half minutes or not. Click to visit the City of Denver's mobility action plan page.