1. 2/7/2006Michael Dixon1 CE 578 Highway Traffic Operations Lecture 3: Passing maneuvers, sight distance, and zones

2. 2/7/2006Michael Dixon2 Objectives Understand basic passing maneuver components Relate passing sight distance to passing maneuver Understand basis for AASHTO and MUTCD passing zone standards Derive AASHTO standard implications on acceptable gaps

3. 2/7/2006Michael Dixon3 Passing Maneuver Assumptions for AASHTO Overtaken vehicle behavior Passing vehicle trailing behavior Passing driver behavior Passing vehicle acceleration After passing clearance length

4. 2/7/2006Michael Dixon4 Passing Maneuver Basic Components d 1 - perception and reaction time distance. d 2 - distance passing vehicle occupies left lane. d 3 - clearance distance between the passing vehicle and the opposing vehicle after passing. d 4 - distance traversed by an opposing vehicle.

5. 2/7/2006Michael Dixon5 Passing Maneuver Basic Components

6. 2/7/2006Michael Dixon6 Standard Values for Estimating d 1, d 2, d 3, and d 4

7. 2/7/2006Michael Dixon7 Estimating Required Passing Sight Distance v= average speed of passing vehicle (mph) t 1 = time of initial maneuver (sec) a= average acceleration (mph/sec) m= difference in speed of passing vehicle and passing vehicle (mph) t 2 = time passing vehicle occupies the left lane (sec)

8. 2/7/2006Michael Dixon8 Passing Sight Distance Estimates (approximation of Exhibit 3-6)

9. 2/7/2006Michael Dixon9 Important Points Assumptions for calculating sight distance What does each component of the passing maneuver represent? How do you estimate the distances of the four passing maneuver components? In the passing maneuver, which components should be used to determine passing zone length?

10. 2/7/2006Michael Dixon10 Basis for Passing Zone Standard (MUTCD) 85th or posted or statutory speed limit (mph) Minimum Passing Sight Distance (ft) 25450 30500 35550 40600 45700 50800 55900 601000 651100 701200

11. 2/7/2006Michael Dixon11 Comparison of MUTCD and AASHTO Design Standards MUTCD

12. 2/7/2006Michael Dixon12 AASHTO Standard Gap Acceptance Implications

13. 2/7/2006Michael Dixon13 AASHTO Standard Gap Acceptance Implications (cont.) Smallest safe time gap for passing? –Assume: start pass –Assume: oncoming vehicles traveling speed of passing vehicle d 2 + d 3 + d 4

14. 2/7/2006Michael Dixon14 AASHTO Standard Gap Acceptance Implications (cont.) Gap time = (d2 + d3 + d4)/(opposing vehicle speed)

15. 2/7/2006Michael Dixon15 AASHTO Standard Gap Acceptance Implications (cont.) Passing (and opposing) vehicle speed (mph) d2 + d3 + d4 (ft) Gap (sec) 2863915.5 3278516.7 3693817.7 40109718.6 44126119.5 47138620.1 51155820.8 54168521.2 57180721.6 60193221.9 64210222.3 66219022.6