Traditionally, traffic simulation models were developed independently for different facilities (e.g. freeways, urban streets, etc.). A wide variety of simulation models exists for various applications [for a review]Koutsopoulos:1992. Representative models, classified according to their representation of traffic flow, are:
Most of these models were developed for evaluation; and few for
real-time support of ATIS operation and traffic prediction
(e.g. DYNASMART, DYNAMIT). Most of the old generation models (for
example, NETSIM, FRESIM, FLEXSYT-II, and earlier versions of AIMSUM2)
do not represent vehicle paths. They use intersection turning
proportions to determine vehicle movements and hence are not suitable
to simulate route guidance. In some simulation models (for example,
NETSIM), control elements such as pretimed and adaptive signal
controls exist. However, the control logic is ``hard coded'' in the
same simulation program. One exception is FLEXSYT-II, a DOS-based
microscopic simulation tool for intersection design and traffic signal
control studies. It allows users to specify the control algorithm in
a specially designed formula language [Middelham et al.(1994b)].
Recent development of FLASH - A FLEXSYT
Application Shell - is underway in the Netherlands
. FLASH includes a MS-Windows based
network editor and improved user interface. It also has the ability
to program a tested control logic into an EPROM to be used in a
real-world operational controller unit.
In conclusion, these microscopic models cannot effectively meet the requirements of evaluating integrated ATIS and ATMS applications at an operational level, because they have limited representation of travel behavior or are inflexible in modeling more advanced surveillance and control systems.
A new generation of traffic simulation models have been developed (or are under development) for ITS applications. Examples are AUTOS, METROPOLIS, DYNASMART, DYNAMIT, INTEGRATION, THOREAU, and AIMSUN2. AUTOS is a macroscopic traffic model developed for ATMS applications at traffic management centers such as testing signal optimization, emergency vehicle response management, and human factors. The simulation model in METROPOLIS, DYNASMART, DYNAMIT, and INTEGRATION are mesoscopic, designed mainly for dynamic traffic assignment applications. THOREAU is a microscopic model developed for ITS evaluation. However, it has a very long running time. AIMSUM2 is also a recently developed microscopic traffic simulator for ITS analysis which has a k-shortest path based routing algorithm and limited simulation of pretimed signal controls [Barcelo and Ferrer(1995), Barcelo et al.(1996)]. Other microscopic simulation models are also under development for modeling Automated Highway Systems [Eskafi et al.(1996), Gollu and Varaiya(1996)].
While these models have all been successfully applied in particular studies, a common shortcoming is the relatively limited range of applications. Some of them are designed for particular applications and useful only for specific purposes, while others do not support advance surveillance and control systems or integrated networks. No model has the integrated componentry and functionality required for evaluation of dynamic control and route guidance strategies on general networks.
The emerging ITS technologies add new functionalities to traffic management systems, such as mainline traffic control, real-time route guidance, and incident management. The lack of an integrated simulation environment with realistic user behavior for ``real time'' traffic management studies has become a bottleneck in ATMS and ATIS research and development. The need for the development of a more sophisticated methodology and simulation tools has been pointed out by a few researchers, including [Santiago and Kanaan(1993), Lin(1993), Underwood and Gehring(1994)]. Enhancement of existing models and development of new models was motivated by these requirements. For example, FHWA has been revising its simulation tools to satisfy the requirements of ITS applications [Santiago and Kanaan(1993)]. Two of its popular microscopic traffic simulators for freeways (FRESIM) and urban networks (NETSIM) have been combined into a more general traffic simulation framework called CORSIM [FHWA(1996)] to which vehicle path processing is being added. [Leonard II(1993)] and [Jayakrishnan and Rindt(1996)] described a simulation approach called ``Testbed Simulation Workbench (TSW)'', a framework for a hybrid simulation environment which communicates with real-time traffic surveillance and control systems.
The simulation laboratory developed in this research seeks to overcome overcoming some of the limitations mentioned above. Its major differences from the existing approaches are: