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Guide to Calculating Mobility Management Benefits Victoria Transport Policy Institute


Least Cost Transportation Planning Example

Least Cost Planning (also called Integrated Planning) refers to planning that:

  • Considers supply and demand investments on an equal basis.

  • Uses a standard measurement of costs and benefits for evaluating investments.

  • Incorporates all costs, including environmental and social costs as much as possible.

Least Cost transportation planning allows mobility management programs to be compared equally with roadway capacity expansion. As an example, consider a transport problem facing Olympia, Washington. Travel between the city’s downtown and its Westside neighborhood was limited by the capacity of a bridge. A $10 million widening project was proposed to increase bridge capacity by 1,200 vehicles per peak-hour, or 1,248,000 additional annual trips. The project’s annualized cost was $1,018,522, or $0.81 per additional peak period vehicle trip. The project would have the following travel impacts:

  • 1.

    Shorten some trips by allowing more direct routes. Although shorter trips usually reduce external costs, downtown Olympia is very sensitive to traffic impacts (congestion, noise, barrier effect, etc.) so this is unlikely to provide overall savings.

  • 2.

    Encourage some longer trips which increase external costs.

  • 3.

    Generate some new trips. This increases external costs, especially due to downtown Olympia’s sensitivity to increased traffic.

  • 4.

    Shift trips to peak periods. This increases costs, including congestion on other roads.

The external costs of the generated traffic can be calculated, assuming the additional trips are divided equally among the four effects described above, as summarized in Table 25. The annualized costs of bridge widening include the $1,018,522 in direct construction costs, plus $2,982,720 in external costs, totaling over $4 million per year, $3.20 per additional trip, or more than $7.40 per additional round trip commute. A mobility management option should be chosen if it can reduce traffic congestion on the corridor for less than $4 million. Various mobility management programs could be evaluated and the most cost effective options implemented until a goal (such as 1,200 peak hour trips reduced) or budget constraint is reached.


External Cost


Change -1,248,000 1,248,000 2,496,000 2,496,000 4,992,000

Per Mile None $0.61 $0.61 $0.28

External Cost $0 $761,280 $1,522,560 $698,880 $2,982,720

Table 25

External Traffic Cost Impacts from Increased Bridge Capacity


  • 1.

    Average trip length reduced by 4 miles.

  • 2.

    Average trip length increase by 4 miles.

  • 3.

    Generated trips, average 8 miles.

  • 4.

    Shift from off-peak


Increasing road capacity increases total motor vehicle use. The additional external costs should be considered when evaluating transportation investments.


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