1. 2/8/2006Michael Dixon1 CE 578 Highway Traffic Operations AASHTO Grades

2. 2/8/2006Michael Dixon2 Objectives Model vehicle operations on grades using the AASHTO Green Book Classify critical grades

3. 2/8/2006Michael Dixon3 Vehicle operating characteristics passenger cars trucks RVs

4. 2/8/2006Michael Dixon4 Modeling vehicle operations using Exhibit 3-59

5. 2/8/2006Michael Dixon5 Modeling vehicle operations using Exhibit 3-59 (cont.) Example 1: –Truck entry speed = 70 mph –Grade = 5% –Grade length = 10,000 ft –Reduced speed = –Speed reduction = Example 2: –Truck entry speed = 50 mph –Grade = 3% –Grade length = 4,000 ft –Reduced speed = –Speed reduction = Exhibit 3-60 and 3-61 are used in like manner

6. 2/8/2006Michael Dixon6 Critical grade lengths The critical grade is the maximum length of a designated upgrade on which a loaded truck can operate without an unreasonable reduction in speed. [pp 242 of the AASHTO Green Book]

7. 2/8/2006Michael Dixon7 Input data for critical grade length evaluation Design vehicle –Truck –RV Grade entrance speed –Level approach –Downgrade approach –Upgrade approach Minimum acceptable speed

8. 2/8/2006Michael Dixon8 Minimum acceptable speed or speed reduction Use your judgment Base on maximum speed reduction allowed

9. 2/8/2006Michael Dixon9 Minimum acceptable speed or speed reduction (cont.)

10. 2/8/2006Michael Dixon10 Modeling vehicle operations using Exhibit 3- 63 (70 mph approach speed only)

11. 2/8/2006Michael Dixon11 Modeling vehicle operations using Exhibit 3- 63 (70 mph approach speed only) (cont.) Example 1: –Level approach –Grade entry speed = 70 mph –Grade = 6% –Resulting critical grade length = Example 2: –Upgrade approach grade = 4% –Grade entry speed = 70 mph –Approach grade length = 1000 ft –Resulting approach grade speed reduction = –Grade = 7% –Resulting critical grade length on the 7% grade =

12. 2/8/2006Michael Dixon12 Measuring grade length It is the length of the tangent grade Incorporate vertical curves

13. 2/8/2006Michael Dixon13 Measuring grade length: curve types

14. 2/8/2006Michael Dixon14 Other analytical procedures HCM procedure for two-lane highway specific grades TWOPAS

15. 2/8/2006Michael Dixon15 Assignment 7 Verify that the suggested uses for Exhibit 3-63 are valid. Perform your work by comparing the Exhibit 3-63 results to those you obtain using Exhibit 3-59. Repeat Example 2, done in-class, for the following conditions for both of the aforementioned exhibits:  Upgrade approach grade = 2%  Grade entry speed = 70 mph  Approach grade length = 1000 ft  Grade = 7% Finally, describe how Exhibits 3-59, 3-60, 3-61, 3-62, 3-63, and 3-64 should be used to evaluate grades for the use of climbing lanes and why the HCM is necessary in some instances.