
Traffic Signal Timing Manual: Chapter 4 – Traffic Signal Design - rinesh
http://ops.fhwa.dot.gov/publications/fhwahop08024/chapter4.htm
======
at-fates-hands
One of the local tv stations here did a great story on traffic light phasing.

They first had viewers email them their worst bottlenecks and where they felt
traffic lights hampered their commutes. After several weeks of collecting
angry emails, they narrowed it down to a handful of intersections.

Then they interviewed a local DOT person, and then brought them out to the
worst intersection the viewers identified. The reporter said they spent about
30 minutes working on the lights and signaling. The reporter did say that
traffic was flowing better and there were less cars backed up at the light
after the DOT person corrected some of the signaling issues.

Of course they ended the story by lamenting about how many traffic lights
there are in the city and clearly the DOT have an uphill battle in keeping
every intersection flowing well, but said they spend a lot of time at least
trying to monitor the bad intersections.

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smaldj
You might be interested in the UK's 'Transport analysis guidance: WebTAG':
[https://www.gov.uk/transport-analysis-guidance-
webtag](https://www.gov.uk/transport-analysis-guidance-webtag) (hosted on the
particularly well-designed GOV.UK).

~~~
noir_lord
gov.uk is practically unique in been a successful public facing government
development project.

The people behind it are incredibly talented, they have a blog here
[https://gds.blog.gov.uk/](https://gds.blog.gov.uk/)

It's almost like if you get together a talented team of people, give them a
clear brief and scope and then let them use whatever tools they need you end
up with a good product at the end...

Also good
[https://digitaltransformation.blog.gov.uk/](https://digitaltransformation.blog.gov.uk/)

Also interesting [https://www.gov.uk/service-
manual/agile/index.html](https://www.gov.uk/service-manual/agile/index.html)
which is their manual for providing digital services.

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mikegillman
The word 'bicycle' is mentioned only two times. 'bicyclists' once, 'bike'
none. Why are we officially overlooking a fantastic and common form of
transport?

~~~
enf
The primary author of this document is Peter Koonce, who is a pretty serious
bicycle guy. You might be interested in his blog:
[http://koonceportland.blogspot.com/](http://koonceportland.blogspot.com/)

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kristopolous
I've fantasized about making a more responsive, consistent traffic light for
years. Every time it's the middle of the night and I'm sitting at a red light
for no reason --- or when I figure out that the sensors are broken and I need
to get out of the car and press the cross walk to have the light change, or
when I'm on my bike and have no chance at all to trigger the sensors.

All these things I want fixed. I want stop lights to stop sucking.

I want an unprotected left to have the signal on the opposing side turn red
sooner if there's a lot of people in the queue ... so that more than two cars
can turn per green.

There's countless improvements that could be done but aren't that are purely
in software and would use the same signal installations. We're not moving
mountains here.

But clearly nobody has done this. Stoplights suck exactly the same ways, in
exactly the same amounts, as they did 25 years ago.

And then, instead of making them suck less, we slap cameras on them to make
sure that people put up with the suckage or pay a stiff penalty. "This
technology has annoying bugs that have never been fixed. But luckily, we've
just spent a lot of money on making sure you don't work around them."

Who does that? This is absurd. no new features - just fix the damn bugs.

~~~
enf
The problem with making the opposing red end sooner ("oncoming traffic has
longer green," as the signs say) is that the opposing permissive left turns
that haven't cleared by the end of the yellow are then caught in the
intersection with their signal red and yours still green. The problem is
called the "yellow trap"
([http://en.wikipedia.org/wiki/Yellow_trap](http://en.wikipedia.org/wiki/Yellow_trap)),
and some states, including California, outlaw the practice because it is too
dangerous.

I'm completely with you about wanting everything demand-actuated to be very
responsive, though. Traffic signals are all engineering with no user interface
design at all.

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koliber
I wonder how many man-hours it took to develop this document. It is thorough
and easy enough for a layman to understand. If we had such specifications when
building software systems, life of programmers would be much easier.

~~~
darksim905
You know, that makes me realize that when you slap "profit" over it all (e.g.,
red light cameras) it sucks up that system so bad.

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Spooky23
Thanks for posting this. My city is getting ready to start putting in red
light cameras, with the supposed goal of improving traffic safety. This should
come in handy when they optimize for revenue.

~~~
joshavant
I was thinking about this the other day. Many articles claim this happens, but
few include real world before/after measurements.

You should take timings + videos of pre- and post-camera activity, for future
reference! It might make a nice compliment to yet another 'they shortened
yellow light timing' article.

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Cerium
GREAT FIND! Very interesting read. I liked the parts about how lack of concern
for pedestrians in the system is a legacy issue. Also interesting is the
segment on stop bars for high speed stops. I never considered that the light
stays yellow extra long to let cars clear! I've always thought "Good choice
Phil, you got through on the yellow all the way." It appears that some of
those lights stay yellow until the car is through! (TSTM Ch 4: 4.7.4)

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brendannee
NACTO released the Urban Street Design Guide with more pedestrian, transit and
bike friendly designs last year. Here is their chapter on traffic signals:
[http://nacto.org/usdg/intersection-design-
elements/traffic-s...](http://nacto.org/usdg/intersection-design-
elements/traffic-signals/)

Several state DOTs have endorsed the NACTO USDG.

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FredDollen
A recent trip to the UK was enlightening for me. Their roadways have a
fraction of the traffic lights and stop signs that we have on the east coast.
We need to remove stoplights from lightly trafficked intersections. For heavy
use intersections, replace with rotaries. The glut of suburban stop signs need
to be replaced with yield signs.

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mwexler
Fascinating read. Thanks for posting.

I did get a chuckle out of the header: "21st century operations using 21st
century technologies". The lady doth protest too much, methinks.

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stevep98
All of this may be irrelevant soon:

[http://www.cs.utexas.edu/~aim/](http://www.cs.utexas.edu/~aim/)

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kimmel
Now thats some good documentation.

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RyanMcGreal
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