Calibration and Validation for Simulation Models in Developing Countries Using VISSIM Case Study - Alexandria City, Egypt
Mohamed Shahin, Alexandria University &ndash; Egypt, Mohamed Bordiny, Tanta University – Egypt
The main goal of this paper is to develop a procedure for simulation model calibration and validation in Alexandria City, Egypt as a case study from developing countries using VISSIM.
Advances in computational technology along with the increased complexity of roadway design and management have created an environment in which microscopic simulation models have become useful tools for transportation engineers. Many research works have been done in order to assist the calibration and validation process for different condition in the developed countries. However, in developing countries this process does not stand for a sufficient tool for the traffic engineers in order to calibrate/validate their models. This may be due to the fact that the road environment in developing countries is much different from that of many developed countries and as a result the guidelines and studies which are produced in the developed nations cannot be used without modification or suggesting new concepts. For example, mixed traffic streets where all traffic modes are moving without separation in the same place interact closely with the everyday life of people. In addition, the vehicles are apt to conflict with stationary obstacles, such as illegal vendor’s occupancy and illegal suddenly drop-offs.
Since car following behaviour is the core of traffic modelling in microscopic models, most model parameters influence the longitudinal dynamics of single vehicles. Calibration of these parameters requires measurements on the level of single vehicles, i.e. data about headways, perception thresholds and driver characteristics have to be available. The amount of random fluctuation differs from driver to driver. Although these parameters are important for the calibration/validation process of the microscopic models, other important paramours should be adapted/included for the traffic simulation in developing countries. These parameters should consider illegal drop-off, sudden humps, absence of marking, sudden pedestrian crossing, etc.
The main goal of this paper is to develop a procedure for simulation model calibration and validation in Alexandria City, Egypt as a case study from developing countries using VISSIM. The traffic behaviour in at selected road links was identified using the video-analysis system. Beside the traditional traffic characteristics (density, speed and flow), several other indicators/parameters are developed in order to analyze traffic behaviour in such mixed traffic situations. These parameters include: number of conflicts, swerving lateral distance, swerving longitudinal distance, and number of stops. Then the model was settled under calibration process for two different scenarios: 1) using the traditional parameters for developed countries; and 2) using the adapted defined parameters above in addition to the traditional parameters. Then, a comparison has been conducted against the real life traffic characteristics such travel time and queue length, and distributed speed and the model results in both scenarios. The results showed that the adapted parameters produce close results to the real life data when compared to the model calibrated by the traditional parameters.
Association for European Transport