1. Some measures of effectiveness or reliability (or both) improve and none deteriorate, while costs decrease or do not change.

  2. Some measures of costs decrease and none increase, while no measures of effectiveness or reliability change.

Such conditions characterize a proposal that clearly is what decision analysts term "nondominated" (as discussed in Chapter 5), and the decision that improvement has occurred is straightforward. Even if one of these conditions is not met, however, performance may be judged to have improved if the community gives sufficiently greater weight to the measures that have improved compared with those that have not. For example, residents of some neighborhoods request installation of speed bumps on their local streets even if their. taxes are raised to recover the public works expenditure. These residents prefer to sacrifice their riding quality to achieve the improved safety they attribute to reduced speed of other vehicles passing through the neighborhood.



Agencies and researchers in Oregon, Pennsylvania, Louisiana, and Minnesota, to name only a few, have presented their work in national forums. Finland and the members of the European Union are also pursuing such work.


public Works Management Practices, APWA Special Report #59, American Public Works Association, Chicago, August 1991.


They may, however, adjust route alignments or traffic signal timing because the consequent reductions in pollution emitted are more immediate and substantial.


"Confidence level" is a term used in statistics. A parameter that is known to have statistical variation (e.g., the strength of concrete) is estimated by testing samples and then computing from these tests a value for the parameter and the confidence one may have, on the basis of the tests, that the actual value of other (untested) samples are equal to or greater than the computed value.


"Safety factor" is generally defined as the ratio of the projected load at which failure would occur to the maximum anticipated load. A safety factor greater than 1.0 is considered safe. However, because of uncertainties in measurement and projection, common practice and sometimes building codes and other regulations may require that facilities be built and operated with safety factors of 1.5, 2.0, or higher.


"Load factor" is typically defined as the ratio of paid passengers to available seats on an aircraft, as a percentage. An airline might hope to maintain its load factors greater than, say, 65 percent.


The committee did note, however, that their visit to Portland illustrated where a different conclusion was drawn by local decision makers committed to implementing land use, parking, and other incentives or restrictions aimed at increasing transit ridership and discouraging automobile usage for downtown travel. Some stakeholders in the Twin Cities area will undoubtedly continue to maintain interest in rail transit development.


The committee was told that the University of Minnesota, aided in part by funding from the U.S. Department of Transportation, is active in research in this area.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement