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CE 578 Highway Traffic Operations

Lecture 28: Ramp Metering

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Objectives

• Terminology

• Objectives and types of ramp metering

• Local ramp metering

• Coordinated ramp metering

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Terminology

• Meter rate

• Allowable metering rate– MAX = 720 to 900 veh/hr– MIN = 180 to 240 veh/hr

• Vehicles per cycle (usually posted at meter)

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Ramp Metering Objectives and Types

• Local or coordinated

• Platoon-breakup

• Gap-acceptance

• Demand-capacity

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Local Ramp Metering—Platoon-Breakup

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Local Ramp Metering—Gap-

Acceptanceupstream gap detector

detected gap

vehicle released for gap

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Local Ramp Metering—Demand-Capacitymainline detector used to determine metering rate

detected volume = 4800 vph

Design capacity = 5400 vph

Metered ramp upstream of potential bottleneck

Allowed volume = 600 vph

Meter rate of 600 vph or 6.0 seconds per vehicle.

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Coordinated Ramp Metering—Demand-Capacity

• General objective function

Fi

iiMi

mii VVZ

Subject to:

jCV jmj

iMAXV imi

iMINV imi

Where

Fi

iijMi

miij

mj VpVpV

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Coordinated Ramp Metering—Demand-Capacity

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Coordinated Ramp Metering—Demand-Capacity

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Coordinated Ramp Metering—Demand-Capacity

• Setting meter rates

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Coordinated Ramp Metering—Demand-Capacity

• Choosing the next ramp to meter

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Coordinated Ramp Metering—Demand-Capacity

bottleneck

1223 3445

Input 1 bottleneck 2 3 4 Demand Min. rate

2 1 0 0 0 800 6003 0.9 0.1 0 0 800 6004 0.85 0.1 0.05 0 1,000 6005 0.8 0.05 0.05 0.05 9,000 NA

Output

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Coordinated Ramp Metering—Demand-Capacity

• Equation objective

• Second term

• Third term

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Coordinated Ramp Metering—Demand-Capacity