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Old Posted Jun 13, 2018, 11:44 PM
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Pre-Signals Offer The Benefits Of A Dedicated Bus Lane On Smaller Streets

When is a Dedicated Bus Lane Not a Dedicated Bus Lane?


MAY 31, 2018

By LAURA BLISS

Read More: https://www.citylab.com/transportati...a-lane/561509/

Quote:
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Not every street that could benefit from a bus lane could fit one, sadly. On streets with only a single lane available in each direction, bus riders have been generally doomed to suffer. But that doesn’t have to be the case, according to Vikash Gayah and S. Ilgin Guler, two professors of civil and environmental engineering at the Pennsylvania State University, if a “pre-signal” is in the mix.

- Traffic signals that give buses priority at the intersection aren’t uncommon on arteries with dedicated bus lanes. Pre-signals, on the other hand, are a very rare bird of traffic planning: These traffic lights are placed mid-block—“upstream” from regular signalized intersections, as the engineers like to say—and actively change the flow of traffic before vehicles hit the intersection at all. --- This helps avoid conflict and delays amid crosscurrents. In the real world, pre-signals are only known only to exist on few multilane roads in the U.K. and Switzerland. But Gayah and Guler recently developed and simulated a strategy that would allow two-lane, two-way streets to get on board, and essentially create a dedicated bus lane out of thin air.

- To pull it off, both lanes get a pre-signal facing both directions of traffic. The pre-signal on the lane facing the opposite direction of the moving bus stops the flow of cars, so that a segment of the lane becomes clear for a bus to merge into it. Meanwhile, the pre-signal on the lane in the same direction also pauses its flow of cars, allowing the bus to merge back onto its original lane with the stopped cars behind it. This all happens before the main signal, avoiding conflict with cars in the intersection. “You get a de facto bus lane by utilizing the opposite direction lane to jump the queue of cars,” Gayah said in an interview.

- According to the simulations that the authors ran, the time-savings appear to be significant. Pre-signals can save bus travelers 5 to 7 seconds of delay per intersection at uncongested intersections, and up to 30 seconds of delay at congested intersections. “Even though the undersaturated number appears small, this is per intersection and includes buses that experience zero delay,” Guler wrote via email. In other words, even at low-traffic hours of the day, pre-signals could speed buses up. And 30 seconds of time-savings per intersection at rush hour could easily mean a longish-haul bus rider gets home 10 minutes sooner.

- The other benefit of this type of treatment is that it minimizes delays for drivers. The flow of cars is only being stopped in one direction ahead of the main signal, and the intersection still functions normally in all directions once the bus passes through it. That’s important, Guler and Gayah said. Dedicated bus lanes and other kinds of transit-priority signal treatments can actually slow down the flow of traffic for cars, in certain cases. That makes drivers mad, and gives them fuel for arguing against such changes. --- “As advocates, we want to prioritize transit improvements when it’s least impactful to cars, since the majority of people are still drivers,” Guler said. “It won’t be beneficial in the long run to make people unhappy, so we take the holistic approach.”

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  #2  
Old Posted Jun 14, 2018, 1:45 AM
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interesting
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Old Posted Jun 14, 2018, 3:07 AM
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Mind blown. So simple but I would have never thought of it.
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Old Posted Jun 14, 2018, 5:12 AM
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How practical is this in the real world? Each signal costs several hundred thousand dollars. If the bus line is busy enough to warrant that kind of expense at every intersection, then it's probably running frequently, so these pre-signals would be freezing traffic on the road every few minutes.

Said roads would become useless for motorists, and while you may see that as a feature and not a bug, consider that the drivers will simply find an alternative, maybe using nearby residential streets if possible or worsening congestion on parallel routes.

I guess this just seems like a solution that doesn't really fit American cities. You need a 2-lane road with no parallel parking or curb cuts, heavy traffic, a popular bus route, and wide intersection spacing. Those factors don't come together very often in the US. It might work better in inner-ring suburbs in Europe, which often have certain features of the big city but in a weird suburban megablock format that is very different than the suburbs Americans are used to.
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