This paper describes the development and initial ﬁeld testing of an intelli- gent traffic control system for identifying and progressing platoons at isolated traffic signals on signalized arterials. This system uses advance detection to obtain real-time information about the presence and speeds of individual vehicles. Its algorithm identiﬁes whether a platoon—of a user- speciﬁed minimum size and density—is approaching the signal and esti- mates platoon arrival time at the stop bar. When warranted, the system issues a low-priority preemption signal to progress the detected platoon. Duration of the initial preemption signal is based on estimated arrival and departure times for the smallest acceptable platoon and the estimated time needed to clear any queues present at the signal. Then, the system switches to an extension mode and provides progression to any additional vehicles determined to be in the platoon. It accomplishes that by increasing pre- emption time until no more vehicles are determined to be in the platoon or until the max timer expires. The system also ensures that the last pro- gressed vehicle is not trapped in its dilemma zone. The platoon identi- fication and accommodation system can be implemented by retrofitting existing National Electrical Manufacturers Association cabinets. Motorists often encounter urban or suburban signal-controlled inter- sections operating in isolated (semiactuated or fully actuated) mode. Often, these intersections are located not too far from other signal- ized intersections. Such intersections operate efficiently during the periods when light traffic arrives from upstream intersections or when there is balanced demand at all approaches. However, often platoons arriving at these intersections are forced to stop, causing driver frustration and unnecessary delay. A study of platoon behav- ior on arterials showed that platoons remained together for distances of up to 2,000 m (1). This research also showed that optimal timing of downstream signals to accommodate such platoons results in up to a 10% reduction in delay. At many of these intersections, inter- connection with adjacent traffic signals to provide coordination for through traffic is not a feasible approach because of unpredictable ﬂuctuations in traffic demand. A desirable approach is to keep isolated control at these signals, but to provide for dynamic coordination when a need arises. This paper describes the development and ﬁeld testing of an intel- ligent traffic control system that detects platoons of traffic approach- ing the intersection and manipulates the controller to accommodate the detected platoon. The paper begins by analyzing system require- ments. Then it describes the platoon identiﬁcation and accommoda- tion (PIA) system, its in-lab testing, and lessons learned through ini- tial ﬁeld tests conducted at two sites in Texas. The paper concludes by presenting current research to enhance the system. REQUIREMENT ANALYSIS The objective of this project was to develop a hardware–software system that provides the following functionality for one priority direction: • Identiﬁes platoons approaching the signal intersection and • Manipulates controller operation to progress these platoons without unduly taxing conﬂicting movements while maintaining the safety of motorists and pedestrians. These requirements are discussed in the following subsections. Platoon Identiﬁcation Behavior of platoons departing from a traffic signal and traveling downstream has been investigated extensively since the pioneer work by Robertson in 1969 (2). Several researchers have proposed enhancements and methods to calibrate this model (3–5); other researchers have proposed new platoon dispersion and compression models (6–9). Several platoon detection algorithms have also been developed (10–12). Readers interested in a review of some of these models are referred to Denny (13). A key contribution of this paper is the development and ﬁeld testing of a real-time platoon detection and progression system that is used when a platoon’s departure information from the upstream signal is not available. The ability to detect platoons approaching an intersection and deter- mine the lead time needed for controller manipulation before detected platoons arrive at the stop bar requires the use of advance detec- tion. Figure 1 illustrates different variables and constraints that need to be incorporated to determine the optimal placement of advance detector(s). The lower part of this ﬁgure illustrates a moving platoon in time and space. As illustrated in the ﬁgure, a certain number of vehicles must pass over the detector within a speciﬁed time window before the detection algorithm can classify these vehicles as a platoon. By that time the front end of the platoon may have dispersed and moved closer to the downstream intersection (rather, closer to the back of any queue at the downstream signal), and there may not be sufficient time available to manipulate the controller to serve this platoon without stopping it. Thus, advance detector(s) must be located a signiﬁcant distance upstream of the intersection to provide sufficient time for detecting a platoon, the time needed to manipulate the controller oper- ation at the downstream signal, and the time needed to clear any queue Development and Field Testing of Platoon Identiﬁcation and Accommodation System Nadeem A. Chaudhary, Montasir M. Abbas, and Hassan A. Charara N. A. Chaudhary and H. A. Charara, Texas Transportation Institute, Texas A&M University System, 3135-TAMU, College Station, TX 77843-3135. M. M. Abbas, Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, 301-D1 Patton Hall, MC 0105, Blacksburg, VA 24061. 141 Transportation Research Record: Journal of the Transportation Research Board, No. 1978, Transportation Research Board of the National Academies, Washington, D.C., 2006, pp. 141–148.