As a researcher

During his tenure with the School of Civil and Environmental Engineering, Professor Leonard has published twenty-two archival journals articles and fourteen refereed conference proceedings; designed, implemented and distributed eleven software packages; and contributed as principal or co-principal investigator to seventeen successful research proposals that have resulted in over $1,628,000 in sponsored research.

The following sections briefly describe Professor Leonard’s most significant creative contributions in the fields of ITS, traffic system engineering, and computer simulation of transportation systems.

Computer Simulation of Traffic Systems

Professor Leonard’s contributions to the modeling and simulation of traffic systems span a broad range of modeling and data issues. At the high level, in collaboration with Dr. Richard Fujimoto of the College of Computing at Georgia Tech, Dr. Leonard postulated several “Grand challenges in Modeling and Simulating Urban Transportation Systems” (2002), and in collaboration with Dr. Billy Williams and two doctoral students, Dr. Leonard proposed a “Systematic Approach for Validating Traffic Simulation Models” (2004). At the detailed level, Dr. Leonard postulated a simplified kinematic wave approach for the study of merge bottlenecks (Ni and Leonard, 2005) and general networks (Ni, Leonard, and Williams, 2006.) From a data quality and implementation perspective, Dr. Leonard developed an imputation scheme for overcoming missing data (Ni, Leonard, Guin and Feng, 2005) and further explored markov chain methods within this framework (Ni and Leonard, 2005.) Additionally, Dr. Leonard has contributed to the estimation of air quality impacts of transportation improvements using computer simulation (Washington, et al. 1998; Bachman, et al. 1998; and Roberts, et al. 1999).

Bridging academic research and the transportation profession, Professor Leonard’s work in the software development arena clearly demonstrates a talent to effectively deliver the latest research results to the practicing professional. The software package WEST (“other intellectual products” Leonard, 1995a) was developed to satisfy a need identified by Professor Leonard through his work with graduate students and his participation in professional short courses. WEST represented the first tool for the direct comparison of signal timing policies and provides insights on the multi-objective nature of signal timing design. Several innovative concepts embodied in WEST, including side-by-side comparison of multiple simulations, top-down organization of measures of performance, multiple views to the input data from a single panel, and custom speed editing tools, promote the effective and efficient use of the software by both graduate students and practicing professionals. WEST was distributed nationally through the Center for Microcomputers in Transportation (McTrans.) Further, all the help files, screen menus, and output reports have been translated and incorporated into a Spanish-language version of WEST (named METS) also available from McTrans. The software package McT7F (“other intellectual products” Leonard, 1998) presented a WinNT/95 user interface to the current FORTRAN-style interface of the TRANSYT-7F simulation and optimization software. McTrans selected Professor Leonard to design and implement a new interface to TRANSYT-7F, a simulation model used by over 1400 traffic engineers (as documented by McTrans) around the world for developing coordinated signal timing plans. By implementing professional design techniques in all his software, Dr. Leonard has enhanced the usability and broadened the impact his work on the traffic engineering community.

Analysis and Design of Intelligent Transportation Systems

Professor Leonard is actively engaged in helping define the field of Intelligent Transportation Systems (ITS), a field that combines sensors, communications systems, computer and decision support systems, and traveler information systems into a seamless, integrated system with the goals of improving safety and reducing congestion on our nation’s highways. As a member of the Deployment Technical Advisory Group (1998), an advisory panel established by ITS America at the joint request of the Federal Highway and Federal Transit Administrations, Dr. Leonard provided policy guidance for allocation of over $300 million in ITS Research and Development. At the request of the World Bank and the International Road Federation, Professor Leonard discussed “ITS and Traffic Operations” as part of the Second Executive Conference on Transportation and the Environment (1997), and “ITS: Connecting the Americas” for the Universidad Metropolitana in Caracas, Venezuela (1996). Additionally, Dr. Leonard’s design ideas have been incorporated into chapters of two books (Leonard and Meyer, 1995; Leonard and Meyer, 1997).

Analysis and Design of Traffic Systems

Professor Leonard’s contributions in the area of traffic engineering fall primarily in the optimal design of signal systems. Based on signal timing evaluation and training data gathered over an eight year period from 1985 to 1993 for southern California cities, Leonard and Recker  (1997a) documented signal timing policies used by practicing engineers to reduce congestion in traffic signal systems. A signal timing policy is a set of operational goals applied when developing a timing plan for a system coordinated intersections. These policies may include maximizing progression along the main street, minimizing system-wide delays, minimizing stops along the arterial, minimizing system-wide fuel consumption, or minimizing queue lengths at critical intersections. Based on the observations of these studies, Dr. Leonard proposed a methodology for consistently comparing these alternatives and applied this framework to propose guidelines for selecting the appropriate policy for different situations (Leonard and Rodegerdts, 1998b). Results of this analysis are significant to engineers searching for inexpensive, congestion-reducing alternatives because they provide guidelines for selecting appropriate timing policies. When improved signal timing strategies do not provide enough additional capacity to meet demand, the traffic engineer may decide to add capacity to the physical roadway. In Leonard (1995), Professor Leonard describes the operational characteristics of triple left turns (i.e., intersections with three left turn lanes servicing a single direction.) Results demonstrated that these designs offer increased throughput without severely impacting delays on opposing movements. As a result of the publication of this paper, Professor Leonard received requests from several jurisdictions around the country (including Gwinnett County, Georgia and Sacramento, California) for additional information about this congestion-relieving design alternative. Results of this paper have been incorporated into the Highway Capacity Manual (2000), arguably the most influential reference for transportation engineers, and a key reference document for the civil engineering professional engineering examination.