vehicle flow. homework ch 3 # 1,4, 7, 15 vehicle flow how do vehicles operate in the system...
TRANSCRIPT
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Vehicle Flow
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Homework
• Ch 3 # 1,4, 7, 15
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Vehicle Flow
• How do vehicles operate in the system– capacity– speed – headway– density
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Time Space Diagrams
• Show vehicle location vs. Time– one way or two way– any type of transportation system– used to find
• siding placement
• progression
• minimum headways
• throughput
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Example• Canal System - Cohoes and Schenectady are on the Erie Canal
approximately 10 miles apart. There is a lock 3 miles from Schenectady. On the canal, barges cannot pass each other except in opposite directions ( the mules get tangled otherwise). The canal lock can raise or lower 1 barge in 20 minutes. it takes an additional 20 minutes to return the lock to its original position to handle another barge going in the same direction. Barges move at 5 mph. 3 barges can be accommodated at the lock either upstream or downstream until it is their turn to move through the lock. Barges leave Schenectady every 20 minutes and Cohoes every 30 minutes. Does the system work or should the schedule be revised?
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Vehicle Following
• Spacing needed for stopping
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Deceleration
• 3 types of deceleration– normal– emergency– instantaneous
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Example
• Ch 3 # 2
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Flow Concepts
• 4 variables– volume– speed– density– headway
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Volume
• # of vehicles passing a given point in a given unit time
• q = n/T
• cars per hour
• does not tell you anything about speed or density
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Speed
• 2 types– Space Mean Speed
• distance divided by time
• useful in determining vehicle flow characteristics
– Time Mean Speed• Spot speeds
• Radar gun
• not useful except for tickets
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Example
• Si = 2 miles, i = 1 - 5
• v1 = 42 mph, v2 = 39 mph, v3 = 47 mph, v4 = 50 mph
• m1 = 3.1 min, m2 = 2.8 min, m3 = 3.3 min, m4 = 3.0 min
• What is the difference, is it significant?
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Density
• Concentration– vehicles per unit length– cars/mile
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Headway
• Time or distance between two vehicles– h = 1/q gives the time headway– h = 1/k gives distance headway– which is more useful?
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Relationships
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Relationships
• q=uk– basic relationship
• Important points– jam density– jam speed– max volume
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Relationships
• Shape of curves– what do they tell us?
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Example
• Ch 3 # 8
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Shock waves
• Happens when traffic is forced to change speed either slowing down or speeding up
• Can move either forward or backward
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Example
• Ch 3, # 15
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Pedestrians
• LOS based on– speed– flow rate– v/c ratio
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Bike LOS
• Based on amount of hindrance
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Examples
• Ch 4. # 1, 2
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Homework
• Ch 4 #3,10, 12, 15, 16, 21,25,31, 36,37,48
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Control of Vehicle Flows
• Control vehicles– minimize accidents– maximize effectiveness
– transit
– airports
– roadways
• Channelization most common control
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Control of Vehicle Flows
• Speed limits
• Control on Links– signage– lane width– number of lanes– headway rules
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Headway Rules
• RR - uses block system
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Headway Rules
• Aircraft– Airports
• 1 aircraft on runway at any time
• separation distances – 2.5 miles between aircraft
– 10 miles horizontal / 2000 ft vertical in air
– Control based on aircraft location
• Ground control for aircraft not on runway
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Capacity
• Capacity based on mode
• # of vehicles per hour
• # of passengers per hour
• arrivals, departures per hour
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Highways
• Capacity varies by road type– Freeways
• no controls,
– Intersections• traffic control
– 2 lane & 4 lane roads• lead vehicle
• All use Level of Service
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Level of Service
• LOS can be based on– delay per vehicle– speed– service flow
• 6 LOS A - F– A is best– F is worst
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Determining Capacity
• Based on Roadway geometrics and traffic conditions
• For Freeways– can determine ideal conditions and from that a
maximum capacity
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Peak Hour Factor
• Measures demand peaking
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Example
• Ch 4. # 11
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Freeway Capacity
• LOS based on – density– speed– v/c
• For an LOS can find Maximum Service Flow (MSF)
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MSF
• MSF = qmax*(v/c) - ideal conditions
• SF = q = qmax*N*fw*FHV
• Table 4.3.3 for heavy vehicle factors
• Table 4.3.2 for width factors
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Capacity Restrictions
• Non recurring
• Recurring
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Example
• Ch 4 # 14
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Airports
• Capacity depends on landside and airside
• LOS is based on delay and total time
• Why are airports becoming shopping malls?
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Rail
• Mass transit– LOS based on pass/seat, space/ pass,
• both peak and off peak
• AMTRAK– LOS based on wait time, comfort, pass/seat