The Most Viable Alternative for the 5-Points Intersection

Where are roundabouts appropriate?

Roundabouts may be particularly advantageous for:

  • Replacement of all-way stops
  • Rural intersections with high-speed approaches
  • Freeway interchange ramp terminals
  • Intersections with complex geometry, skew angles, and more than four approaches
  • Replacement of signal controlled intersections where unbalanced proportions of certain movements greatly decrease signal efficiency
    • Roundabouts generally process high volume left turns more efficiently than all-way stop control or traffic signals
  • 3-leg intersections with heavy left turn volume
  • Replacement of two-way stops when side street delay becomes excessive
  • Intersections with a high crash rate or a higher severity of crashes
  • Closely spaced intersections
  • Intersections with high U-turn movements
  • Intersections near schools
  • Transitions or “Gateways” from higher speed to lower speed areas
    • Roundabouts control speed through geometry
  • Where aesthetics are important
  • Where accommodating senior drivers and pedestrians is an objective
    • Older users are particularly at risk at intersections and roundabouts offer key safety benefits
More than half of these are characteristic of the "5-Points" intersection but they have been largely ignored by the decision makers.  Now is the time for action.  The problem is not going to be solved by ignoring it while also dismissing the most promising solution.  The most recent proposal from OCCAM Engineering is quite absurd because it adds another signal controlled intersection where too many already exist.  See it here.

Huitt-Zollars Preliminary Sketch

Click image to enlarge

In this sketch, the city's consultants used abnormally large roundabouts.  The outside diameter of the each roundabout is about 230 ft. Size matters with roundabouts and smaller is generally better.   In practice the actual size of each roundabout is more accurately represented by the area shaded in green, or between 150 and 190 ft  maximum diameter.

Concept Sketch

A Double Roundabout at the "5-Points" Intersection


Click on image for a better view

This amateur sketch demonstrates that two modern roundabouts of modest size will essentially fit within the two existing signalized intersections.  Roundabouts are a great solution at intersections where right of way constraints exist, where there are a high number of left turning movements, and where business access is a  consideration.  Professional analysis and design is required to accurately model the performance of roundabouts for a particular location. The results of the generic model evaluated by the city's consultants, while encouraging, are misleading because it will always under-perform a properly designed solution.

TRB Roundabout Conference 2011


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