Date: Sun, 27 Feb 2011 12:08:23 -0800
From: "tonyrvt@ACEWEB.COM" <tonyrvt@ACEWEB.COM>
Subject: Re: Walker Crash Rates and Traffic Volumes/single-2-lane roundabouts
Per:
Thank you for the study. Carefully read this document which gives a helpful assessment of Swedish roundabout experience well into their roundabout production. One-lane roundabout experience in Sweden confirms the Schoon and van Minnen the dimension of safety in a Netherlands study at about the same point in time. Two-lane experience did not confirm UK findings of substantial safety improvement over signals. Will look at the bicyclist assessment in the VTI study in a separate message.
The Swedish study of about 7% of the 700 roundabouts there in 1997 provides a useful picture of walking and bicycle mode safety data. Note that based on the study projection of Swedish roundabout population of about 1500 today (2010) then the number of roundabouts per million population for France (30,000), Sweden and the US (3000) amounts to:
France 500
Sweden 161
US 10
Using these figures and applying them to state like Vermont (just over 600,000 population) which now has 8 roundabouts, the French equivalent level is 300 and Swedish equivalent is 97.
Walker safety
Note in the 1990s even though general safety gains were observed, there were still questions from nation to nation on safety, particularly for walkers and bicyclists where roundabouts were already on the ground in significant numbers and with those numbers growing rapidly.
This study examined whether or not roundabouts improved safety for walkers and bicyclists. This section evaluates the walking mode data.
The value of the Swedish study stems from the reporting by number of lanes both the number of walkers and traffic volume. In addition speeds were evaluated and posted speed
effects were reported. Finally, the existing prediction model for VTI used on non-roundabout intersections (one VTI signal and non-signaled intersection formula was based on
finding the rates based on numbers of walkers and traffic volumes found no significant difference in injury crash numbers). In addition a formula for predicting roundabout walker crashes--a separate formula for single and two lane roundabouts).
The walker safety conclusion:
The results suggest that roundabouts pose no problems for pedestrians
compared to conventional or signal controlled intersections.
Given the finding of walker safety “pose no problems†at roundabouts compared to non-roundabout intersections, the study also pointed out single lane roundabouts better safety performance than two lane roundabouts.
The speed findings--higher speeds at roundabouts with higher speed limits, higher speeds when the local speed limit is lower than the through road limit, and two lane speeds higher than single lane--point to the basic relationship of speed and crash frequency, the higher the speed the greater the frequency and the more severe the injuries. The VTI study data confirms these basic parameters in the case of walker crashes at roundabouts.
The one-lane roundabouts average daily traffic volumes were 11,066 and walkers 486. The two-lane numbers were 23,375 and walkers 1,338.
One-lane findings included a reduction of walker crashes versus predicted of 73%, 100% less of serious injuries and 75% less than light injuries. For two-lane roundabouts all elements were slightly higher (crashes, fatalities [1 versus 0.1], and light injuries) than the predicted while the category serious injuries were lower at the roundabouts, 2, than predicted, 2.8. Per Garder has stated that the two-lane roundabouts at the time of the study were somewhat larger than those installed today. Presumably higher speeds at larger designs would also reflect higher crash rates and more severe injuries.
Finally consider the roundabout density at the time of this study, about 100 per million population compared to France in 2003 of 500. At some point there appears to be a multiple roundabout factor (MRF) where the speed influence of one roundabout interacts with adjacent roundabout(s) further reducing speeds and therefore very probably both frequency and severity of crashes. And there may be other elements contributing to MRF. (The four lane commercial road with considerable bicycle commuting,South Golden Road, Golden, CO certainly reflects in part a MRF where speeds dropped from 48 mph between intersections to 32 mph when roundabouts were installed.)
Tony Redington
Montreal
New Blog: TonyRVT.xanga.com
Date: Mon, 25 Feb 2013 11:03:41 -0700
From: Phil Demosthenes <pdemos@ECENTRAL.COM>
Subject: Japan now at 10 roundabouts
English newspaper article on Japan's pursuit of roundabouts
as an intersection solution. Japan does have some old large
rotaries, but is now looking at modern 30 meter diameters
(not sure it that is the island or ICD). US single lane is
35-45 meters ICD.
Notable is discussion, an estimate, on how failed signals
during the Great East Japan Earthquake added to the number
of fatalities. So serious consideration is being given to
roundabouts as improving evacuation efficiency and safety.
As many of you know we had a contingent of visitors from
Japan at the Carmel 2011 conference following the earthquake
and there was also a presentation at the Kansas city 2008
conference.
Our next TRB conference is in Seattle, April 16-18, 2014. So
try to include you travel expenses in your upcoming 2013/14
fiscal year budget.
Recent News article
http://www.yomiuri.co.jp/dy/national/T130224003955.htm
Hideki Nakamura presentation: Kansas RBT conf 2008
http://www.teachamerica.com/rab08/RAB08S5ANakamura/index.htm
Philip Demosthenes
Consultant
Denver, Colorado
303-349-9497
phil@pdemos.com
www.pdemos.com
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