Browsing by Author "Prasanga, HN"

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item: Conference-Abstract
Application of dynamic traffic assignment and determine model parameters for urban traffic conditions in Sri Lanka
(Sri Lanka Society of Transport and Logistics, 2020-11) Prasanga, HN; Fernando, PRD; Gunaruwan, TL
The travel behaviour of people on a road network is not often constant and it changes over the time. Drivers who use a particular road network continuously tend to find more comfortable, congestion free routes with least travel time to reach their destinations. This scenario is complicated in the context of a congested and high-density urban road network where drivers have more freedom to use alternative paths to reach their destinations based on changing traffic patterns within short periods. Further, the presence of navigational tools such as Google Maps help the drivers in making quick decisions in selecting congestion free routes, making route selection more dynamic. In order to address this dynamic environment, many microsimulation traffic models around the world have developed the dynamic traffic assignment tool which provides the traffic modeller a more realistic modelling environment for urban traffic over the conventional static route assignment. Further, conventional static route assignment may not be able to simulate and give realistic results for urban areas with complex route networks. However, this facility available in the microsimulation traffic models has not yet been tested under Sri Lankan conditions. Therefore, the objective of this study is to test the dynamic traffic assignment process and find the model parameters that are compatible with Sri Lankan traffic conditions and driver behaviour. For this purpose, PTV Vissim traffic microsimulation software was used. A 2.5 km stretch of A 000: Kollupitiya-Sri Jayawardenapura road and its vicinity (comprising Rajagiriya junction and flyover) have been considered for the case study. Manual vehicle number plate surveys were carried out at 14 predefined locations covering the entire area to develop origin-destination matrices for different vehicle classes. The average growth factor method was used to develop working matrices from the sample matrices developed through this number plate survey. The origin destination matrices developed for the period between 5.00 pm and 6.00 pm were used as the input for the traffic model. Stochastic (Kirchhoff) traffic assignment method was used to distribute traffic between zones in Vissim. Model convergence, calibration and validation were carried out as per the Vissim manual and Traffic Modelling guidelines developed by Transport for London Institute. The GEH static values of input and output flow values of the modelled network were used as the parameters for model calibration and validation. The road network developed in Vissim was successfully calibrated to local conditions and a set of model parameters that were compatible with Sri Lankan conditions found. However, there is a need for future research work to find model parameters that are compatible with different road and traffic conditions.
item: Conference-Abstract
Guideline to select appropriate locations for centre median openings
(Department of Civil Engineering, University of Moratuwa., 2017-07) Prasanga, HN; Pasindu, HR; Pasindu, HR
Medians are paved or landscaped areas in the middle of roadways that separate traffic travelling in opposite directions. A raised median with well-designed median openings is one of the most important tools to create a safe and efficient highway system. Moreover, it reflects the degree of access management of the particular highway. At the moment, it can be clearly identified that many urban roadways in Sri Lanka are being rehabilitated and improved to multi-lane facilities with introducing raised road centre medians. Therefore, the provision of centre median openings for right turns, cross traffic movement & “U” turns is essential. However, at the moment, there is lack of proper guidelines or a methodology available within road agencies in Sri Lanka to follow when deciding the appropriate locations for median openings of a particular highway. Most of the time frequent changes occur to the initial designs of the centre median and median opening locations due to the unavailability of a proper guideline. Often, there are lots of public requests for new median opening locations and it is very difficult to handle public requests in the absence of a proper guideline resulting delays to the centre median construction, deviating the objective of safety and proper access management. Therefore, this study is focused on developing a suitable guideline for the median opening selection process. The proposed guideline has been developed based on some of the international access management guidelines and incorporating local considerations. Decision making criteria when justifying median opening locations is somewhat complex in nature since there is no proper legal framework available in Sri Lanka for access management. Road network connectivity, road safety, traffic efficiency, right turning traffic volume density, the positioning of road side developments is some of the factors which influence the decision for selecting a proper location for median opening. The PTV VISSIM microscopic simulation model was used to optimize the selected median opening locations with respect to travel time and total delay of the road network. Vissim model has been used intensively around the world for such kind of access management experiments. The median opening selection process is a complex process with regards to our country since we don’t have an access management policy. Therefore, it is very important to note that the median opening spacing are site specific and we cannot recommend a general spacing value for a road or a road section. If we go for general spacing values, that may be incorrect to use with the uneven positioning of by roads and different turning movement densities. Therefore, it is very difficult to provide a constant spacing for median openings in our road network. However, we can practice a minimum spacing value depend on functional requirements and safety.