Thursday, September 1, 2011

Professional peer review of the MIG design study for roundabouts on Trinity Drive

The Ourston Roundabout Engineering Peer Review Report has been received and is available to review on the County website. If you would like to review the report, please use the following address:

Here are the findings and recommendations. Boldface is mine.

Findings and Recommendation

Our analysis shows that single lane roundabouts will not adequately handle the
existing or future traffic volumes for select approaches.
The capacity predictions for
these critical entries are generally below the traffic volumes, resulting in V/C ratios
exceeding 0.85. It is not recommended that roundabouts be designed with V/C
ratios exceeding 0.85 as queuing and delay estimations are highly variable and

The use of roundabouts to address the purpose and need of this corridor study is
applicable. Roundabouts can provide a safety improvement for all users, improve
the modes of travel, and support social and economic vitality. It is recommended
that roundabouts with an appropriate lane configuration to handle the projected
traffic volumes be considered. Even though right-of-way constraints are compact,
careful design of multi-lane roundabouts which only require minimal and strategic
right-of-way takes would make this alternative viable. An evaluation of a multi-lane
roundabout alternative against the conventional intersection alternatives may prove
to result in the same evaluation consensus where roundabouts are the preferred

Yours truly,
Troy Pankratz, P.E.
Project Manager


Steve A said...

I find multiple-lane roundabouts quite easy to safely cycle through, unless those are the kind of roundabout that is designed for high speed motorized transit. These are rare in Texas and in Washington State.

Chandra said...

I have seen a few of these in Grapevine, TX. They are easy to ride through.

Peace :)

Khal said...

I think a reasonably skilled cyclist could handle single or multilane roundabouts, although some literature I've read suggests multilane roundabouts have higher crash rates for bicyclists and motorcyclists.

My bone to pick was with the assumption that the proposed treatment would encourage bicyclists who were not riding to take up riding and that the proposed infrastructure would keep them safe. I rambled on about that back in April, if anyone wants to dig back in the April posts.