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Vehicle Flow

CE-160 Transportation Engineering. Vehicle Flow. Homework. Ch 3 # 1,4, 7, 15. Vehicle Flow. How do vehicles operate in the system capacity speed headway density. CE-160 Transportation Engineering. Time Space Diagrams. Show vehicle location vs. Time one way or two way

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Vehicle Flow

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  1. CE-160 Transportation Engineering Vehicle Flow

  2. Homework • Ch 3 # 1,4, 7, 15

  3. Vehicle Flow • How do vehicles operate in the system • capacity • speed • headway • density CE-160 Transportation Engineering

  4. 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 CE-160 Transportation Engineering

  5. 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? CE-160 Transportation Engineering

  6. Vehicle Following • Spacing needed for stopping CE-160 Transportation Engineering

  7. Deceleration • 3 types of deceleration • normal • emergency • instantaneous CE-160 Transportation Engineering

  8. Example • Ch 3 # 2

  9. Flow Concepts • 4 variables • volume • speed • density • headway CE-160 Transportation Engineering

  10. 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 CE-160 Transportation Engineering

  11. 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 CE-160 Transportation Engineering

  12. 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? CE-160 Transportation Engineering

  13. Density • Concentration • vehicles per unit length • cars/mile CE-160 Transportation Engineering

  14. Headway • Time or distance between two vehicles • h = 1/q gives the time headway • h = 1/k gives distance headway • which is more useful? CE-160 Transportation Engineering

  15. Relationships CE-160 Transportation Engineering

  16. Relationships • q=uk • basic relationship • Important points • jam density • jam speed • max volume CE-160 Transportation Engineering

  17. Relationships • Shape of curves • what do they tell us? CE-160 Transportation Engineering

  18. Example • Ch 3 # 8

  19. Shock waves • Happens when traffic is forced to change speed either slowing down or speeding up • Can move either forward or backward

  20. Example • Ch 3, # 15

  21. Pedestrians • LOS based on • speed • flow rate • v/c ratio CE-160 Transportation Engineering

  22. Bike LOS • Based on amount of hindrance

  23. Examples • Ch 4. # 1, 2

  24. Homework • Ch 4 #3,10, 12, 15, 16, 21,25,31, 36,37,48

  25. Control of Vehicle Flows • Control vehicles • minimize accidents • maximize effectiveness • transit • airports • roadways • Channelization most common control CE-160 Transportation Engineering

  26. Control of Vehicle Flows • Speed limits • Control on Links • signage • lane width • number of lanes • headway rules CE-160 Transportation Engineering

  27. Headway Rules • RR - uses block system CE-160 Transportation Engineering

  28. 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 CE-160 Transportation Engineering

  29. Capacity • Capacity based on mode • # of vehicles per hour • # of passengers per hour • arrivals, departures per hour CE-160 Transportation Engineering

  30. Highways • Capacity varies by road type • Freeways • no controls, • Intersections • traffic control • 2 lane & 4 lane roads • lead vehicle • All use Level of Service CE-160 Transportation Engineering

  31. Level of Service • LOS can be based on • delay per vehicle • speed • service flow • 6 LOS A - F • A is best • F is worst CE-160 Transportation Engineering

  32. Determining Capacity • Based on Roadway geometrics and traffic conditions • For Freeways • can determine ideal conditions and from that a maximum capacity CE-160 Transportation Engineering

  33. Peak Hour Factor • Measures demand peaking CE-160 Transportation Engineering

  34. Example • Ch 4. # 11

  35. Freeway Capacity • LOS based on • density • speed • v/c • For an LOS can find Maximum Service Flow (MSF) CE-160 Transportation Engineering

  36. 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 CE-160 Transportation Engineering

  37. Capacity Restrictions • Non recurring • Recurring CE-160 Transportation Engineering

  38. Example • Ch 4 # 14

  39. Airports • Capacity depends on landside and airside • LOS is based on delay and total time • Why are airports becoming shopping malls? CE-160 Transportation Engineering

  40. Rail • Mass transit • LOS based on pass/seat, space/ pass, • both peak and off peak • AMTRAK • LOS based on wait time, comfort, pass/seat CE-160 Transportation Engineering

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