I'm not an engineer but have read a lot of this literature. I guy I
know from Georgia Tech, Eric Dumbaugh (now at Texas A&M) has done a
lot of good work on this.
Basically, as the article says, we've tried to make roads straighter
and wider in the name of safety, even banning benches and landscaping
in the "recovery zone" next to urban arterials (which is where the
sidewalk is, which says a lot about whose safety is being considered).
But that strategy invites speeding. Speed limits have little effect --
as we will see in Madison if we do as the alder wants and lower the
speed limit on Stoughton Road without changing the design.
The literature is still developing, so it's hard to precisely predict
how traffic will behave in all situations. But in general, these types
of measures are thought to help reduce speeds:
* Narrow lanes. The Green Book allows for 10-foot lanes, but generally
we build arterial and even collector lanes much wider. I did a speed
study on one with 15-foot lanes -- very few drivers heeded the 30 mph
limit and some were going nearly double that.
* Reduce building setbacks to lessen the wide-open feel.
* Do "road diets," e.g. by replacing four-lane streets with TWLTLs.
(TWLTLs let the most conservative driver set the pace.)
* Install landscaping and other elements -- even curves -- that don't
allow drivers to see down the road forever. (I'm not suggesting blind
intersections, just enough variation in the passing landscape to
require attention; Dumbaugh finds a major safety benefit.)
* Mark pavement or use special pavers to indicate pedestrian crossings.
* Allow small trees, benches, etc. -- nothing that would kill a
motorist should he/she veer into it -- in the "recovery zone."
* Time stoplights for the speed limit and post signs indicating this.
(A variation -- can't remember where this is: a light that turns red
when it senses speeding. Add a red-light camera and you have a pretty
fool-proof speed reduction strategy. Though it probably violates the
MUTCD warrant on when to install traffic lights.)
* Replace highway-style signage with more traditional urban signs, and
rename urban streets that have the word "highway" in them to "street,"
"boulevard," etc.
Eric
From: Jay Ferm
<[email protected]>
To: [email protected]
Sent: Tue, March 30, 2010 12:52:18 PM
Subject: [Bikies] road design impacts considered
www.infrastructurist.com
has an interesting article on how road design
impacts road speed:
http://www.infrastructurist.com/2010/03/23/can-roads-control-your-driving-the-truth-about-safety-enhancing-road-design/
My classic example of this in Madison is the stretch of Atwood Ave
adjacent to Olbrich Gardens. I've gotten two speeding tickets here.
The speed limit is marked as 25mph but traffic routinely travels at
40+ mph. I maintain this is due to the road being designed for higher
speed than it's marked. This stretch is wide open, few trees impinge
on the roadway, buildings are set far back. It LITERALLY is DIFFICULT
to respect the speed limit here. Both times I was ticketed I was
traveling at the prevailing speed of traffic. (I am not offering an
excuse for my driving. Just an observation. I broke the law and I
willingly paid the fine.)
IF the posted speed limit is what is considered safe; AND if the
preponderance of traffic on a road travel at a speed drivers consider
safe and comfortable; AND if the preponderant speed is higher than the
posted speed; THEN we are designing roads to operate at unsafe speeds.
What other examples do you have from the Madison area of roads
designed to operate at unsafe speeds?
What should we do to address this issue? From an engineer's
perspective, what's the issue here?
Best,
Jay Ferm
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