1. The document discusses different traffic assignment models used to estimate traffic volumes on road networks. 2. Minimum path models assume users will select the fastest route between origins and destinations, using algorithms like all-or-nothing, multipath, or capacity restraint to allocate traffic. 3. All-or-nothing assigns all traffic to the free-flow minimum path, while multipath and capacity restraint distribute traffic across multiple paths according to costs like travel time, updating as volumes increase.

1. Traffic Assignment (Route
Choice)
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2. Trip Assignment
• Trip makers choice of path between origin and
destination
• Path: streets selected
• Transit: usually set by route
• Results in estimate of traffic volumes on each
roadway in the network

3. Minimum Path
• Theory: users will select the quickest route
between any origin and destination
• Several route choice models (all based on some
“minimum” path)
– All or nothing
– Multipath
– Capacity restraint

4. Minimum Tree
• Starts at zone and selects minimum path to each
successive set of nodes
• Until it reaches destination node
1
2
3
4
5
(3)
(4)
(2)
(4)
(7)
Path from 1 to 5

5. Minimum Tree
1
2
3
4
5
(3)
(4)
(2)
(4)
(7)
1. Path from 1 to 5 first passes thru 4
2. First select minimum path from 1 to 4
3. Path 1-2-4 has impedance of 5
4. Path 1-3-4 has impedance of 8
5. Select 1-2-4

6. All or Nothing
• Allocates all volume between zones to
minimum path based on free-flow link
impedances
• Does not update as the network loads
• Becomes unreliable as volumes and travel
time increases

7. Multi-Path
• Assumes that all traffic will not use shortest path
• Assumes that traffic will allocate itself to alternative paths
between a pair of nodes based on costs
• Uses some method to allocate percentage of trips based on
cost
– Utility functions (logit)
– Or some other relationship based on cost
• As cost increases, probability that the route will be chosen
decreases

8. Capacity Restraint
• Once vehicles begin selecting the minimum
path between a set of nodes, volume
increase and so do travel times
• Original minimum paths may no longer be
the minimum path
• Capacity restraint assigns traffic iteratively,
updating impedance at each step