Citation

Wanat J. Transp. Res. A Gen. 1983; 17(2): 115-120.

Copyright

(Copyright © 1983, Elsevier Publishing)

DOI

10.1016/0191-2607(83)90065-1

PMID

unavailable

Abstract

This paper notes the inability of analysts to evaluate the impact of certain policy interventions because of sparse nominal level data. Using the premise that knowing the limits of what could have happened will assist the investigator to know what did happen, this research enumerated all possible solutions or, in real world terms, scenarios that represent changes in driving behavior before and after the imposition of the 55 mph limit in 1974 on Michigan freeways. The enumeration tallied extreme values of all cells and some cell groupings in the 3x3 table representing the speed changes from 1973 to 1974. Enumeration of all possible solutions also yielded information about the likelihood that certain cells exceeded others. In some cases non-obvious and absolutely certain knowledge about interrelationships among some cells was uncovered. Substantively this investigation demonstrated that those 1973 drivers who travelled relatively fast modified their driving behavior more radically than those who were closer to the new 1974 speed limit.