The design, developed by the National Institute of Justice (NIJ), consists of program elements that will be uniformly implemented in 3 city police departments in the 100-500,000 population range and evaluated by NIJ. The rationale for the system lies in several studies indicating 1) that only a minor percentage of calls coming into a police department concerns crimes in progress or medical emergencies for which a rapid mobile response is necessary 2) and that the rapid response is effective for urgent crime-related incidents. Moreover, studies show that while citizens react negatively to delayed police responses when police are required immediately, they are willing to forgive a delay if a reasonable cause is given at the time they call for help. Although various types of differential response systems are currently being used by police departments as a means for classifying calls to determine appropriate response and priorities, few departments have developed a comprehensive differential response system in which the full range of possibilities is addressed. Furthermore, most of these systems are plagued with a number of problems, such as confusion over priority designations for in-progress calls, basic patrol critical calls, and basic patrol calls, and increased travel time caused by indiscriminate adherence to first-come, first-served dispatch within priorities. Goals of the field-test program are to assure that the most urgent calls for service receive priority treatment, that the rate of noncritical calls for service handled by immediate mobile response is reduced, and that the rate of critical calls handled by mobile response is increased. Additional goals are to increase the use of delayed mobile response for noncritical calls and to increase the rate of noncritical calls handled by nonmobile response. The program components include a new call classification scheme to categorize calls along certain dimensions; a range of response techniques, including immediate mobile response, delayed mobile response, and nonmobile response, along with several options within each of these response classes; and various changes in call-intake procedures. Participants will also be required to comply with a number of planning, reporting, and training requirements and will have to evaluate the implemented program to assess the impact of the system on police practices and on citizens and the feasibility of program transfer. Sections of the report contain information on implementation, NIJ support, and site selection criteria. Tabular data, footnotes, and a glossary are included, and 12 source materials are appended.