1 / 7

Lec 12 TD-Part 5: ch5.4.4, H/O, pp.498, Intro to trip assignment

Lec 12 TD-Part 5: ch5.4.4, H/O, pp.498, Intro to trip assignment. Lecture Objectives. Know the purpose of trip assignment Know a few names of trip-assignment procedures Know the difference of minimum-path techniques and minimum-path with capacity restraints. Trip Assignment.

lois-whitaker
Download Presentation

Lec 12 TD-Part 5: ch5.4.4, H/O, pp.498, Intro to trip assignment

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lec 12 TD-Part 5: ch5.4.4, H/O, pp.498, Intro to trip assignment Lecture Objectives • Know the purpose of trip assignment • Know a few names of trip-assignment procedures • Know the difference of minimum-path techniques and minimum-path with capacity restraints

  2. Trip Assignment Trip assignment is the procedure by which the planner predicts the paths the trips will take. The planner can get realistic estimates of the effects of policies and programs on travel demand.

  3. Minimum-path techniques (+ “all-or-nothing” trip loading) Assumption: Travelers want to use the minimum impedance route between two points. Given impedance values, assignment algorithms find minimum paths (or shortest paths) to get from point A to all other locations (to which trips are distributed). A skimtree is created from 1 to all other nodes (see next slide).

  4. Minimum-path techniques (+ “all-or-nothing” trip loading) (cont) A skimtree is created from 1 to all other nodes. Travel time Previous node In this method, all trips between a given origin and destination are loaded on the links comprising the minimum path and nothing is loaded on the other links.  No consideration of the link capacities.

  5. Minimum path with capacity restraints Once you reach this point travel time exponentially increases. Capacity restraints attempts to balance the assigned volume, the capacity, and the related speed (translated to travel time). Travel time increases as traffic volume on the link increases because of interaction between the drivers and their perception of safety because they slow down as volume increases. Several methods are available, but the most popular one is the Bureau of Public Roads model.

  6. The BPR model Where TQ = travel time at traffic flow Q T0 = “zero-flow” or “free-flow” travel time = travel time at practical capacity x 0.87 Q = traffic flow (veh/hr) Qmax = practical capacity = ¾ x saturation flow alpha & beta = parameters (need calibration) See the example on page 500. Note that this example assumes that the ratio of daily flow/capacity is equal to hourly flow/capacity.

  7. Two other methods discussed in the text • Davidson’s model Tau = LOS parameter, 0.1-0.2 for freeways, 0.4-0.6 for urban arterials, 1.0-1.5 for collector roads • Greenshields’ model (See Example 13)

More Related