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Introduction to Transportation Systems

Introduction to Transportation Systems. PART II: FREIGHT TRANSPORTATION. Chapter 15: Railroad Terminals: P-MAKE Analysis to Predict Network Performance. Terminals. Terminal performance is a major determinant of network performance. Terminal Performance. Variability in Arrival of

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Introduction to Transportation Systems

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  1. Introduction to Transportation Systems

  2. PART II: • FREIGHT TRANSPORTATION

  3. Chapter 15: Railroad Terminals: P-MAKE Analysis to Predict Network Performance

  4. Terminals • Terminal performance is a major determinant of network performance. Terminal Performance Variability in Arrival of Incoming Trains Figure 15.1

  5. Terminal Performance:Another Look Performance lower performance “robust” plan higher performance “sensitive” plan Variability in Arrival of Incoming Trains Performance includes a measure of cost -- if one is measuring terminal performance not only on throughput of the terminal but also on the resources used -- robustness may involve a more conservative use of resources. It may involve having redundancy in the system. Figure 15.2

  6. LOS and Routing over theRail Network • Level-of-service in rail freight operations is a function of the number of intermediate terminals at which a particular shipment is handled. • Empirical research shows the major determinant of the LOS is not the distance between origin and destination, but rather the numbers of times the shipment was handled at intermediate terminals, which is really an operating decision on the part of the railroads.

  7. Direct Service Figure 15.3

  8. Terminal Operations Classification Yard Classification Bowl Receiving Yard Departure Yard Inbound Train Hump Outbound Train

  9. A P-MAKE Function f (AVAIL) I.0 P-MAKE 2 hr 8 hr 12 hr AVAIL Available time in terminal in hours (AVAIL) Figure 15.5

  10. Average Yard Time Now, average yard time -- E(YT) -- will be a function of the available time (AVAIL) to make that connection. In this model, E(YT) -- the average yard time -- will have two components -- the time spent in the yard if the connection is made, in which case, with probability P-MAKE, the terminal time is AVAIL. With probability (1 - P-MAKE), the car will spend (AVAIL + the time until the next possible train). E(YT) = P-MAKE * (AVAIL) + (1 - P-MAKE) * (AVAIL + time until next possible train)

  11. E(YT) for a given P-MAKE function “sweet spot” AVAIL We can calibrate these curves and calculate an “optimal” AVAIL for the particular terminal. Figure 15.6

  12. Origin-DestinationPerformance 12 hrs. 12 hrs. 12 hrs. Origin Destination Figure 15.7

  13. P-MAKE Functions f (AVAIL) more efficient terminal less efficient terminal AVAIL Figure 15.8

  14. Another P-MAKE Function f (AVAIL) AVAIL Figure 15.9

  15. Missed Connection 0 1 2 Yard Time (for Probability AVAIL = 8 for both yards) [f(AVAIL)]2 16 2 f(AVAIL)*[1- 40 f(AVAIL)] [1-f(AVAIL)] 2 64

  16. Total Yard Time as a f(Avail) Probability AVAIL = 8 f(AVAIL) = P-MAKE = 0.9 Total Yard Time Probability AVAIL = 8 f(AVAIL) = P-MAKE = 0.9 Total Yard Time f(AVAIL) = P-MAKE = 0.9 Average O-D Time = 56.8 Variance O-D Time = 103.7 f(AVAIL) = P-MAKE = 0.8 Average O-D Time = 61.6 Variance O-D Time = 184.3 Figure 15.10

  17. Available Yard Time

  18. More Frequent Trains (1) • P-MAKE Function • Total Yard Time f (AVAIL) P-Make = 0.9 AVAIL Probability ƒ (AVAIL) = P-Make = 0.9 Twice daily frequency Total Yard Time Figure 15.12, 15.13

  19. More Frequent Trains (2) • So, by having trains run twice a day, the average yard time and variance of yard time goes down. • This system is a more expensive system, but provides a better level-of-service. This is the classic cost/LOS trade-off [Key Point 14].

  20. Bypassing Yards Total Yard Time with Bypassing One Yard Probability Total Yard Time Figure 15.14

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