14 - Chapter7-Signal Timing

14 - Chapter7-Signal Timing - Signal Timing TTE 4004...

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Signal Timing TTE 4004 10/26/11
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Saturation Flow Rate Saturation headway: h =headway achieved by stable moving platoon of vehicles passing through a green indication Saturation Flow Rate: every vehicle assumed to occupy h seconds of green time, and if signal always green, then s vehicles/hour could enter intersection s = 3600/ h
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Saturation Flow Rate s = 3600/ h If signal always green, could simply multiply by the number of lanes to estimate the capacity of the approach. *units of measure: vehicles per hour of green time per lane, (vphgpl) Can find saturation flow 2 ways Field observations Estimation Similar to method for estimating FFS
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Discharge Headway Discharge headway: time passage between successive vehicles as they cross the curb line during a green phase. Measured at rear wheels of vehicles. First headway longer than others. Includes driver reaction time, and acceleration time. Second headway shorter, reaction and acceleration times overlap. Eventually headways level out, typically around 4-5 vehicle. Once this occurs, saturation headway can be measured.
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Discharge Headway
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Signal Phasing Phase: green interval, plus change interval and clearance intervals for a particular movement Cycle: sum of all phases Usually 60 to 120 seconds
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Exclusive Turn Phases HCM guidance for protected left turns When the product of left-turn vehicles and opposing vehicles (through and right) exceeds, during peak hour 50,000 for one opposing lane 90,000 for two opposing lanes 110,000 for three opposing lanes
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Example 7.6 Do any of the approaches need protected left-turn phases?
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Solution Do you need an exclusive left turn phase for WB traffic? WB
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14 - Chapter7-Signal Timing - Signal Timing TTE 4004...

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