Roundabout Fastest Path, Fastest Speeds, and Speed Consistency Calculations as per NCHRP 672 and Torus


One primary influence on the safety performance of a Modern Roundabout are the speeds at which vehicles will travel within the facility. This webinar focuses on the analysis tools and method provided by the NCHRP Guideline to evaluate speed, and then looks at how speed-informed design can be accomplished in the TORUS Roundabouts software.

In this webcast you will learn the following:

  • Learn about the five Critical Path Radii, and specifically what Fastest Path is.
  • Understand what speed consistency is and why it is important.
  • Learn about TORUS’ methodology for approximation of fastest path.
  • Watch how TORUS can be used to check fastest path on manually generated roundabout designs, and also how speed-informed geometric design is performed.

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Take the Quiz

1. NCHRP Report 672 prescribes that the maximum speed differential between movements should be no more than approximately how many mph?
2. Why is speed consistency for roundabout design important for designers and engineers?
3. Which set of offsets (from splitter island, central island, and corners) are used in construction of the through fastest path?
4. You can use the TORUS Roundabout software to evaluate user drawn roundabout designs?
5. What is the maximum number of entry and exit lanes TORUS can currently support?
6. What is R4 in the fastest path methodology?
7. R1<R2<R3 is a condition prescribed in checking speed consistency in a roundabout based on NCHRP 672.
8. The design speed of the roundabout is defined by the smallest radius along the fastest allowable path.
9. Which references did Hannah refer to for the fastest path construction methodology?
10. TORUS is able to handle designs with 5 legs.

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