An occasional update on items from Motordom – the world of auto dominance
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IS SYNCHRONIZING TRAFFIC SIGNALS A GOOD IDEA?
Yes, say some.
Minneapolis is in the midst of an upgrade for its traffic-control system that includes a new computerized system that can re-time traffic signals to make traffic flow more efficiently.
New signal timing is in place downtown; changes in the rest of the city will be complete by next summer. The $11.2 million project is funded by a federal grant and state, county and city money.
City officials say traffic flow downtown could improve by 10 percent. The system also allows the city’s Traffic Management Center to analyze traffic patterns and activate and turn off left-turn arrows.
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No, say others:
“Any time you make it easier or faster or less congested on a road, the more people will drive,” says Dom Nozzi, a transportation consultant based in Boulder, Colo., who blogs at nozziwalkablestreets.com.
“When we introduce changes that make it less inconvenient or less congested, we induce new car trips that would otherwise not have happened,” he says.
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It depends, say Reid Ewing:
It’s difficult, though, to get it right, he says:
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Too often, Ewing says, protected left-turn arrows slow the entire system.
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Cross streets can be given too much time on green lights, slowing traffic on major roads that intersect with them.
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Traffic engineers don’t always update signal intervals to match changes in volume and flow.
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To work correctly, signals must be close to each other or at least a quarter-mile apart. The progression of traffic through irregularly spaced synchronized signals isn’t optimal.
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The thing about traffic lights is many people forget or overlook the colour-blind population. The current traffic signals, either the vertical: red on top, amber in the middle, green on the bottom, or the horizontal: red on left, amber in middle, green on right exist so the signal is not ambiguous to a portion of the population who if they guess incorrectly could plow their steel box into people, property, or traffic. While the hourglass signals are a neat design exercise, they would be useless if applied in real life. Personally, I like the pedestrian count-down timers. When implemented ideally, when the number gets to 0 the light changes to amber. When approaching intersections that use the pedestrian countdown timer, drivers no longer have to play the “I’m running this light if it changes” game in their head.
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“Calgary or Seattle both have a very high ratio job/population. both inner cities foster good transit ridership number by North American standard, but this can be mostly due to a very centralized job market favoring a good transit market share in the CBD rather than a good transit system per sei ” I said here:
http://voony.wordpress.com/2010/04/26/thezurichmodel/
In the meantimes
“condo-isation/gentrification” of their downtown can largely explain the gain in walk/cycling, that is true of most cities (on that front, Washington DC mentioned in the article, is effectively more advanced, but also, less hilly, and less wet, in addition to not have an helmet law…)
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A simple number countdown – like the pedestrian signals is far better than some symbolic signal that will have a portion of the population (and tourists) scratching their heads or squinting to figure out what it is.
Be practical, not “cute”.
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Signal timing can be done for transportation modes other than driving, Copenhagen signal times for cycling. Ahh cycling Mecca.
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A better idea than signal timing would be to lower the speed limit on all city streets (or at least just all downtown streets) to 30. And pedestrian scrambles. Both Speed up traffic.
The terrible thing about signal timing is that it makes uncongested commutes faster but minimally affects rush hour commutes. This is because the number of vehicles lining up will result in the intersection being moved back several dozen metres, negating the signal timing effect (the light turns green right before you approach the intersection). The reason I hate signal timing is not just that it promotes car culture. Since TomTom measures congestion as (trip time during congestion) / (trip time without congestion), and signal timing speeds up the latter, this will just create the illusion that Vancouver is congested. No wonder Vancouver gets #2 spot on most congested city. Vancouver’s signal timing is so well coordinated that rush hour trips may take 10X longer. (Think Smithe Street).
Back to my main point. Pedestrian Scrambles will eliminate turning conflicts, resulting in more free flow. For example, quite often traffic waiting to turn right from Robson onto Thurlow backs up traffic for half a block. The pedestrian barrier only allows one or two cars to turn right per cycle.
The most effective way of managing traffic (and speeding it up) is 30 speed limits. The time saved per kilometre of going (without stopping) of 50 compared to 30 is 48 seconds, in a downtown peninsula that is just 2.5 km wide at its longest. With a 30, lane widths can be significantly narrowed, shortening pedestrian crossing times. Yellow Lights are shorter, and streets can be designed for 30 speeds. Many traffic lights would be removed, as cars would more likely stop for pedestrians, and crashes would decrease. There’s no reason why Vancouver can’t be 30.
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Good stuff for discussions here. It would seem that an intelligently designed adaptive signal system would be ideal for many reasons:
– Improve the efficiency of traffic flow to allow street space to be reclaimed for higher priority modes (pedestrians, cyclists, transit). Obviously this would nene to be done quickly, before induced demand takes the space.
– Create a more flexible signal system that can better provide transit signal priority, and potentially for bikes and peds to some extent, though their arrivals tend to be more random due to varying speeds.
– Get progression speeds right for the conditions of the moment, much like Kyle has said. The progression speeds in downtown Vancouver seem to be set at 50-60 km/h, above the speed limit, wholly unachievable in congested conditions or where geometry is unusual (e.g., Dunsmuir), dangerous for other road users when it can be driven, and a cause of higher traffic noise levels. The Downtown Transportaion Plan had an action to reduce the progression speed to no more than 40 km/h but it has not be implemented. Better still would be an adaptive system that would cap the progression speed at 40 km/h but go lower during congested conditions.
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