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  • This road might not look like anything special.

  • But what if I showed you the same road, a few years earliernotice anything different?

  • Here's a better angle of that: The old road has 4 lanes for traffic.

  • The new one has two.

  • And now there's this middle lane for left hand turns.

  • There's also a new bike lane.

  • This is what transportation planners call a road diet.

  • And it's a very popular to make the roads safer.

  • Over the course of the 20th century, four lane roads became an American institution.

  • It started with the release of Ford's model-T in 1908.

  • A few decades later, there was one car for every two households in the states.

  • By the 1960s, many roads became so busy, that traffic engineers had to figure out how to

  • add capacity.

  • So, they added lanes.

  • A lot of pavement was getting put on the ground.

  • Even where maybe when the population and traffic volumes weren't so high that we needed that

  • pavement.

  • But we wanted that pavement.

  • Sometimes your eyes are bigger than your stomach.

  • Fast forward to the present day and we're left some overbuilt roads that are pretty

  • unsafe.

  • And crash reduction is a major benefit that planners can achieve with just a bit a paint.

  • Four lane roads have quite a few conflict points -- these are places where accidents

  • could happen.

  • These ones represent merging accidents.

  • These are rear ends, and there are multiple left turn crash scenarios.

  • Now look at what a 3 lane reconfiguration doesThere are far fewer crash points.

  • A road diet can also make left turns suck way less.

  • The shared middle lane takes left turners out of the traffic flow, so they won't hold

  • up drivers who want to continue through.

  • And now, left turners will only have to cross 1 lane of traffic instead of 2, which will

  • eliminate broadside accidents.

  • And the benefits don't end there.

  • By slimming each lane in the road, the road diet reduced the travel speed by almost 7

  • miles per hour.

  • Narrower lanes can cause that psychological impact on the driver to slow down a bit.

  • And while a 6 mile an hour difference in speed may seem modest, it can make an auto accident

  • much less deadly ... Narrower lanes also leave more space for expanded

  • sidewalks or bike lanes.

  • your pedestrians will feel safer.

  • It might've given you more green space to separate from your vehicles.

  • And your bicyclists might have a dedicated space to ride.

  • In the midst of these changes, the number of traffic lanes has gone from 2 to 1.

  • So if you drive a car, you might assume that the tradeoff of a road diet would be congestion...

  • How could traffic *not* increase?

  • That's usually their concern before a road diet is implemented.

  • That's not what happens.

  • The volume of the roadway is still sustained.

  • We wouldn't want to put a 4 to 3 conversion on a piece of roadway that would then push

  • half your traffic somewhere else.

  • And what we found in a couple of places, it actually makes moving through town easier.

  • But traffic flow is only one part of the equationyou've got to also balance commercial

  • and safety benefits too.

  • especially if this is through an urban corridor where you've got businesses, coffeeshops,

  • it works.

  • it keeps people moving, it doesn't take traffic away from that corridor, and it reduces

  • those rear-ends that thendo stop the road.

  • Iowa is conducting this road survey because so far, the plan has worked *really* well

  • for them.

  • A study of 15 streets in the state saw a crash reduction rate of nearly 50%.

  • At the same time, the diet didn't substantially disrupt other activities along their corridors.

  • A key factor was the traffic volume, measured by engineers as 'Annual Average Daily Traffic'.

  • Most road diets will run into problems as you approach that 15,000 vehicles number.

  • In Iowa, many roads don't get that much traffic.

  • The same could not be said for the suburban contexts in California.

  • A study comparing road diets in Iowa to corridors in California showed that California's streets

  • average about double the amount of daily traffic.

  • The same kinds of road diets resulted in a 17% crash rate reduction -- significantly

  • lower than the reductions in Iowa.

  • This is not to say that the road diets in California are an outright failure.

  • It's just a difference *context* for the road diet.

  • And the success of a road diet is driven by so many other factors -- economic impact,

  • land use, or level of service to name a few.

  • What works in Iowa may not be the right fit for California, and vice versa.

  • So the case for road diets is pretty clear: they do slow streets down and they do reduce

  • crashes.

  • But whether or not that's worth the trouble depends very much on the context of the world

  • that surrounds the road.

This road might not look like anything special.

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ロードダイエット:より安全な道路を設計する (Road diets: designing a safer street)

  • 189 9
    robert に公開 2021 年 01 月 14 日
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