ANALYSIS OF VEHICULAR INTERACTIONS AT HIGHWAY INTERSECTIONS UNDER MIXED TRAFFIC FLOW

Abstract

The major-minor priority intersection is by far the most common intersection layout in current use in India. Intersections are the critical element of road networks and their characteristics determine the efficiency and capacity of the entire road network system. Consideration of methods of estimating effectiveness and levelof- service of priority intersections shows that despite the considerable amount of research which has already been completed, the possibility of effectively designing and efficiently operating such intersections is still limited, specially under mixed traffic flow as is prevailing in India. The major factors affecting the performance of an semi-urban type uncontrolled (priority) intersection have to be analysed quantitati vely, including parameters such as : approaching traffic volumes on major and minor roads , composition of the approaching traffic, turning flows on minor roads, physical and operating characteristics of motorised and non-motori- % sed vehicles , approach widths, turning radii, length of turning paths, angle of intersection and crossing times and speeds for different type of vehicles. The above factors get further multiplied when the prevailing traffic is of mixed nature, that is, it is mixture of motorised and nonmotorised veicles. As such the cluster of variables is too large to be analysed by any simple intuitive approach. Hence the logical and (ii) ultimate choice is adoption of digital simulation techniques looking to the complexities of mixed traffic behaviour where wide variation in static and dynamic operating characteristics exists, while sharing the same right-of-way. Therefore the scope of this research work has been : (i) To analyse the mixed traffic vehicular characteristics of major vehicle types predominantly available on Indian roads with special reference, to size, approaching and clearing speeds at the inter- section, composition of traffic and manoeuvring characteristics. (ii) The analysis has been carried out on 3-leg and 4-leg semi-urban type uncontrolled (priority) intersections with typical Indian urban and rural traffic characteristics. The semi-urban inter sections are essentially located at the outskirts of urban areas. However , studies have been done on selected representative sites only. (iii) Some impoprtant field studies have been designed to be conducted on the selected sites. The data were collected on these sites through manual method and video recording techniques (VRT). This data were utilized for building and validation of the simulation model. Also they were used as a vital input into the simula tion model SIMMTRA-345 for analysis of traffic ar uncontrolled 3-leg and 4-leg road intersections. The digital simulation model SIMMTRA-345 has been developed in FORTRAN-77 language keeping in view its wide acceptability. The event-scanning procedure has been incorporated in the model as it best (iii) suits the situation to be simulated. It has been explained in the experimental programme, that the simulation programme is also divided in sequential steps and then synthesised to obtain logical and reasonable results of practical, as well as, theoretical importance. Summarised programme is : (i) An initial programme to understand the basic flow process at uncontrolled intersections under mixed traffic flow. (ii) The flow variables are analysed with special reference to timeheadway, intersection clearing timings, approaching and clearing speeds of different type of vehicles, gap acceptance behaviour, approach width and intersection angle. (iii) Mathematical models and statistical distribution synthesising the above results have been derived and built into a digital simulation model 'SIMMTRA-3451. (iv) The delays caused to minor road vehicles, are considered to be the measure of performance to establish the level-of-traffic quality at intersection proper. (v) The concept of vehicular interactions under different traffic and roadway conditions is successfully exploited to obtain the various relationship between input and output parameters. (vi) The simulation software is run on HP-9600 computer system and the results obtained were validated. (vii) The simulation programme is dynamic in its behaviour and elastic, • • (iv) responsive, and sensitive towards static and dynamic character istics of the vehicles considered in the study, approach traffic volumes approach traffic compositions and proportion of turning traffic. (viii) The composition and conflict factors developed in the present study are based on simulated delays. (ix) The new equivalent passenger car values developed for the diff erent of vehicles exclusively for uncontrolled intersections under mixed traffic flow vary depending upon the proportion of conflic ting traffic and non-motorised vehicles in the approaching traffic volumes . (x) The established four levels-of-service are based on the simulated average delay to which the minor road vehicles are subjected. The results of the digital simulation model SIMMTRA-345 provide better and clear insight into the flow variables of mixed traffic flow occuring on uncontrolled priority type semi-urban intersections. . The variables are now availeble in terms of : « (i) Vehicular interactions, time headways between successive vehicles, time headway between same type of vehicles, total delay and average delay experienced by all minor road vehicles and the state of length of queue formed on minor road at any instance of simulation time. (ii) It is possible to have the exact information on the minimum time gap necessary for the different type of vehicles on minor road for clearing an intersection safely. (v) (iii) The various relationships established between input and out put parameters indicate the following results; the delays increase with increased approach traffic volumes, which is rather well expected. the delays increase with increased proportion of conflic ting traffic and non-motorised traffic the delays increase with addition of each additional type of vehicles in the traffic stream. the delays are affected by approach width and increases as the approach width decreases. the delays are marginally affected by angle of inter section and increase as the angle becomes acute. left turning vehicles are not subjected to any delay, except pedestrian crossings . for the same level-of-service, the delays increase with addition of each type of vehicle in the traffic stream. the delay to major road vehicles increases with increased proportion of conflicting traffic in major road traffic stream . Thus it can be conclusively said, that the developed computer software SIMMTRA-345 is capable of providing an indepth insight into the operational analysis of uncontrolled priority type intersections and the work is geographically transferable in view of parameters incor( vi) porated into the model. It may be further added that while the model is applicable to relatively homogeneous traffic also, the work for homo geneous traffic flow is not applicable to the situation analysis herein.