Traffic Assignment

Travel Demand Forecasting: Example Problems

Traffic Assignment

Assign the vehicle trips shown in the following O-D trip table to the network, using the all-or-nothing assignment technique. To summarize your results, list all of the links in the network and their corresponding traffic volume after loading.

Origin-Destination Trip Table:

	Trips between Zones
From/to	1	2	3	4	5
1	-	100	100	200	150
2	400	-	200	100	500
3	200	100	-	100	150
4	250	150	300	-	400
5	200	100	50	350	-

Highway Network:

Illustration of network between zones

[Solution Shown Below]

Solution

The all-or-nothing technique simply assumes that all of the traffic between a particular origin and destination will take the shortest path (with respect to time). For example, all of the 200 vehicles that travel between nodes 1 and 4 will travel via nodes 1-5-4. The tables shown below indicate the routes that were selected for loading as well as the total traffic volume for each link in the system after all of the links were loaded.

Nodes		Link	Travel
From	To	Path	Time	Volume
1	2	1-2	8	100
	3	1-2,2-3	11	100
	4	1-5,5-4	11	200
	5	1-5	5	150
2	1	2-1	8	400
	3	2-3	3	200
	4	2-4	5	100
	5	2-4,4-5	11	500
3	1	3-2,2-1	11	200
	2	3-2	3	100
	4	3-4	7	100
	5	3-4,4-5	13	150
4	1	4-5,5-1	11	250
	2	4-2	5	150
	3	4-3	7	300
	5	4-5	6	400
5	1	5-1	5	200
	2	5-4,4-2	11	100
	3	5-4,4-3	13	50
	4	5-4	6	350

Link	Volume
1-2	200
2-1	600
1-5	350
5-1	450
2-5	0
5-2	0
2-3	300
3-2	300
2-4	600
4-2	250
3-4	250
4-3	350
4-5	1300
5-4	700