This dissertation was concerned with a study of operational controls on urban freeways. An analysis was made of the inbound Gulf Freeway to define the operational problems resulting from vehicular incidents. It was found that significant congestion, delay, and stoppage waves frequently occur on the inbound Gulf Freeway because of the reduction in capacity caused by incidents on the main-lanes. Approximately 80 percent of the incidents reduce the inbound freeway capacity by one-half or more; about 13 incidents per week occur in the study section Monday through Friday from 6 a.m. to 7 p.m. A design concept of a prototype was formulated to increase freeway efficiency by alerting motorists to stoppage waves on freeway sections such as overpasses having restricted sight distances. The prototype was referred to as a safety warning system. It is anticipated that the improved efficiency will result in fewer accidents; reduced system travel time, driver anxiety, and driver discomfort; and improvement in the level of service. Several design alternatives were evaluated. A control technique utilizing critical energy as a parameter was developed and its application to digital computer control of the prototype was investigated. Evaluations were made of the performance, reliability, stability, and sensitivity of the system using a one-lane criterion for control. ...