April 27


HCM 2010 Update – Stop Sign & Roundabout Webinar

By Mike Spack

April 27, 2011

HCM 2010 Unsignalized intersections

Roundabout3 Here are the slides from yesterday's webinar (Download Unsignalized HCM 2010 Presentation).  Highlights from the discussion –


  • This whole chapter is new.  We can finally compute Level of Service for roundabouts!
  • Capacities at roundabouts in the U.S. are currently much lower than capacities observed in other countries.
  • Calculations are based on simple models.  Experience in the U.S. shows roundabout performance is largely impacted by the variability in driver behavior, not specific geometrics configurations.
  • Not included in the Level of Service calculations – geometric configurations (other than number/type of lanes), oversaturated conditions, or interaction effects of upstream/downstream intersections.  Other models should be used if these items are of concern.
  • Delay thresholds are the same as those for stop sign controlled intersections, which are lower than the thresholds for traffic signals.
  • On multi-lane approaches – the volumes in the two lanes are not assumed to be the same.
  • There are calibration tools, which can ideally be tweaked based on local driving behavior data (this is true of the entire HCM 2010).

All Way Stop Sign Control

  • Added methodology to model three lanes of approach instead of just two.
  • New queuing model that is similar to the side street stop sign control method.

Side Street Stop Sign Control

  • Added methodology to model six lane major roads instead of just two and four lane roads.
  • Added methodology for modeling u-turns (our traffic counters will have more to keep track of).
  • More refined method for dealing with the impact from upstream/downstream intersections.
  • Better modeling of impacts of short left turn lane storage and large radii for right turn movements.


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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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