Data were collected via interviews, observations, and reviews of documents issued by the ASAP, the National Highway Traffic Safety Administration, and others. The main changes in Idaho's laws were a reduction in the presumptive level of intoxication from 0.10 percent blood alcohol content to 0.08 percent and mandatory 90-day license suspenion for convicted drunk driving first offenders. The court reorganization increased the Idaho Supreme Court's authority over lower State courts and assigned all but the most serious drunk driving cases to magistrate courts. The main effect of the legislative change was to cause magistrates to withhold judgment during cases rather than to declare offenders guilty. This happened most often in rural areas, where magistates were often nonlawyers who relied more on their personal knowledge of defendants than on the laws. Magistrates also increasingly used withheld judgments to persuade offenders to take part in rehabilitation programs. Presentence investigators were assigned to 67 magistrate courts, not all of which used them effectively. Use of withheld judgments prevented the maintenance of central records and identification of repeat offenders. Results also showed that court reorganization did not increase consistency among the magistrate courts. Magistrates argued that the withheld judgment reduced the number of jury trials and had other advantages. Results supported the hypotheses that legislation alone cannot bring about needed changes, maxmum penalties are rarely used, and lay judges are no less proficient in handling drunk driving cases than are legally trained judges. Other hypotheses and tables are included. For related case studies and a tehnical report summarizing them, see NCJ 72944-45 and 72947-49. (Author abstract modified)