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Special facilities for Heavy vehicle on Steep Grades Chapter 16

Special facilities for Heavy vehicle on Steep Grades Chapter 16. Dr. TALEB M. AL-ROUSAN. Introduction. Large trucks have different operating characteristics than those of passenger cars. The difference increases as the grade of a section of highway increases.

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Special facilities for Heavy vehicle on Steep Grades Chapter 16

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  1. Special facilities for Heavy vehicle on Steep Grades Chapter 16 Dr. TALEB M. AL-ROUSAN

  2. Introduction • Large trucks have different operating characteristics than those of passenger cars. • The difference increases as the grade of a section of highway increases. • It is necessary to consider the provision of special facilities on sections of highways with steep grades carrying high volumes of heavy vehicles. • Two facilities: • Climbing lanes. • Emergency escape ramps.

  3. Climbing lanes • Climbing lane: Is an extra lane in the upgrade direction for use by heavy vehicles whose speeds are significantly reduced by the grade. • It eliminates the need for drivers of other vehicles using the normal upgrade lane to reduce their speed and delay them when passing can not be achieved. • Mostly needed on two-lane highways. • In the past, it was not common due to extra cost. • Recently, they become necessary because of • increased rate of crashes associated with the speed reduction of heavy vehicles on steep sections. • Significant reduction of the capacity of these section when heavy vehicles are present

  4. Climbing Lanes Cont. • The basic conditions that suggest the use of climbing lane is when : • Grade is longer than critical length. • Upgrade traffic flow rate > 200 veh/h • Upgrade truck flow is higher than 20 veh/h. • Critical length: the length that will cause speed reduction of heavy vehicle by 10 mi/h or more. • See Figure 9.13 for performance curves of standard trucks. • The length of the climbing lane will depend on the physical characteristics of the grade (generaly it should be long enough to facilitate rejoining of the heavy vehicle the main traffic stream without causing hazardous conditions.

  5. Emergency Escape Ramps • It is provided on the downgrades of highway for the use of a driver who has lost control of the vehicle because of brake failure. • Objective: To provide a lane that diverges a way from the main traffic stream while the uncontrolled vehicle’s speed is gradually reduced and the vehicle is eventually brought to rest. • Figure 16.27 shows basic types of emergency escape ramps.

  6. Basic Types of Emergency Escape Ramps 1- Sandpile: • loose dry sand. • Provide increased rolling resistance. • Placed on upgrade (+%) to use influence of gravity to stop the vehicle. • Usually not longer than 400 ft.

  7. Basic Types of Emergency Escape Ramps Cont. 2- Descending grade 3- Horizontal grade • 2&3 do not use the influence of gravity to stop the vehicle. • 2&3 Rely on the increased rolling resistance provided by the arresting bed which is made up of loose aggregates. • 2&3 Can be very long.

  8. Descending grade & Horizontal grade

  9. Basic Types of Emergency Escape Ramps Cont. 4- Ascending grade • Use influence of gravity by applying upgrades • Increased rolling resistance by applying arresting bed. • Relatively shorter than the descending or horizontal grade ramps.

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