CE 578 Highway Traffic Operations

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CE 578 Highway Traffic Operations

• AASHTO Grades

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Objectives

• Model vehicle operations on grades using the
  AASHTO Green Book
• Classify critical grades

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Vehicle operating characteristics

• passenger cars
• trucks
• RVs

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Modeling vehicle operations using Exhibit 3-59
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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

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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

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Input data for critical grade length evaluation

• Design vehicle
• Truck
• RV
• Grade entrance speed
• Level approach
• Downgrade approach
• Upgrade approach
• Minimum acceptable speed

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Minimum acceptable speed or speed reduction

• Use your judgment
• Base on maximum speed reduction allowed

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Minimum acceptable speed or speed reduction
(cont.)
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Modeling vehicle operations using Exhibit 3-63
(70 mph approach speed only)
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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
  

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Measuring grade length

• It is the length of the tangent grade
• Incorporate vertical curves

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Measuring grade length curve types
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Other analytical procedures

• HCM procedure for two-lane highway specific
  grades
• TWOPAS

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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.