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CE 578 Highway Traffic Operations

CE 578 Highway Traffic Operations. AASHTO Grades. Objectives. Model vehicle operations on grades using the AASHTO Green Book Classify critical grades. Vehicle operating characteristics. passenger cars trucks RVs. Modeling vehicle operations using Exhibit 3-59.

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CE 578 Highway Traffic Operations

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  1. CE 578 Highway Traffic Operations AASHTO Grades Michael Dixon

  2. Objectives • Model vehicle operations on grades using the AASHTO Green Book • Classify critical grades Michael Dixon

  3. Vehicle operating characteristics • passenger cars • trucks • RVs Michael Dixon

  4. Modeling vehicle operations using Exhibit 3-59 Michael Dixon

  5. 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 Michael Dixon

  6. 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] Michael Dixon

  7. Input data for critical grade length evaluation • Design vehicle • Truck • RV • Grade entrance speed • Level approach • Downgrade approach • Upgrade approach • Minimum acceptable speed Michael Dixon

  8. Minimum acceptable speed or speed reduction • Use your judgment • Base on maximum speed reduction allowed Michael Dixon

  9. Minimum acceptable speed or speed reduction (cont.) Michael Dixon

  10. Modeling vehicle operations using Exhibit 3-63 (70 mph approach speed only) Michael Dixon

  11. 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 = Michael Dixon

  12. Measuring grade length • It is the length of the tangent grade • Incorporate vertical curves Michael Dixon

  13. Measuring grade length: curve types Michael Dixon

  14. Other analytical procedures • HCM procedure for two-lane highway specific grades • TWOPAS Michael Dixon

  15. 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. Michael Dixon

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