1. Intersection Sight Distance (ISD) – AASHTO Method
Alaska Department of Transportation & Public Facilities
Intersection Sight Distance (ISD) – AASHTO Method
Chris Post, P.E.
February 2013

3. Why the need for this presentation?
Seward Meridian – Phase I
Naomi Drive
Public voiced concerns to the Project Engineer about an unsafe condition
Initially, we said it met Standards
Upon further review, we saw that we’d been using the wrong Standard and indeed, there was a legitimate claim
Blame, Mass Hysteria, and Panic Ensued!

5. General Guidance for ISD
Highway Preconstruction Manual (HPCM)
Figure Highway Design Criteria Summary
3R Projects – PCM Section 1160
All Urban and New/Reconstruction Rural Projects – Green Book
Integrity ∙ Excellence ∙ Respect

6. HPCM - Design Criteria Highway Design Criteria Summary (Fig. 1100-3)
Project Design Criteria (Fig )
Driveway Sight Distance Figure (Fig )

7. General Guidance for ISD – cont’d
2001/2011 AASHTO Green Book
Chapter 9 – Intersections
Section 9.5 – Intersection Sight Distance (reference from 2011 GB)
Integrity ∙ Excellence ∙ Respect

8. Intersection Cases Case A – Intersections with no control
Case B – Intersections with stop control on minor road
Case C – Intersections with yield control on the minor road
Case D – Intersections with traffic signal control
Case E – Intersections with all-way stop control
Case F – Left turns from the major control
Integrity ∙ Excellence ∙ Respect

9. Intersection Cases – (cont’d)
Case B – Intersections with stop control on minor road
Case B1 – Left turn from the minor road
Case B2 – Right turn from the minor road
Case B3 – Crossing maneuver from the minor road
Case F – Left turns from major road
Integrity ∙ Excellence ∙ Respect

13. Graphical Solution
First step was to look at the proposed design and determine the ISD…

15. Naomi Mathematical Solution
Several Factors must be considered
Total Number of Travel Lanes
Number of Travel Lanes Crossed for Left Turn
Number of Travel Lanes Crossed for Right Turn
Median +/or Turning Lane Width
Design Speed
Highway Grade (moving Left to Right)
Minor Road Approach Grade

16. Naomi Calculations
Calculation Form

17. So what was the outcome???

18. Final Solution

19. Questions?