Although laws governing moving-traffic violations are fairly uniform throughout the United States, the effective levels of enforcement of these laws vary dramatically from city to city. Basing this study on statistics from nearly seven hundred police departments, census data, personal interviews, on-the-spot observation, and detailed case studies of four Massachusetts cities--Lynn, Waltham, Malden, and Cambridge--Mr. Gardiner identifies and discusses the factors that determine police decisionmaking in relation to traffic violations.

After a brief description of the role of...