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This paper specifies the relationship among various factors contributing to road accidents including geometrical design characteristics, environmental and traffic specifications, by multiple regression analysis. The main objective of this paper is identification of problems associated with the safety issue of road networks by application of accident prediction models. Data from previous accidents were used to develop the models. Results of this study showed that the rate of road accidents is to a large extent dependent on the rate of traffic volume. Type of road and land-use are other important factors influencing the number and intensity of accidents. The mountainous roads in this respect require special attention regarding their safety factors. The quantitative rate of road safety upgrading has also been specified by adding traffic lanes in road networks.

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This paper presents a novel approach to solve the double-track railway rescheduling problem, when an incident occurs into one of the block sections of the railway. The approach restricts the effects of an incident to a specific time, based on which the trains are divided into rescheduled and unchanged ones, so that the latter retain their original time-table after the incident. The main contribution of this approach is the simultaneous consideration of three rescheduling policies: cancelling, delaying and re-ordering. A mixed-integer optimization model is developed to find optimal conflict-free time-table compatible with the proposed approach. The objective function minimizes two cost parts: the cost of deviation from the primary time-table and the cost of train cancellation. The model is solved by CPLEX 11 software which automatically generates the optimal solution of a problem. Also, a meta-heuristic solution method based on simulated annealing algorithm is proposed for tackling the large-scale problems. The results of an experimental analysis on two double-track railways of the Iranian network show an appropriate capability of the model and solution method for handling the simultaneous train rescheduling. The results indicate that the proposed solution method can provide good solutions in much shorter time, compared with the time taken to solve the mathematical model by CPLEX software.

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Pedestrians are among one of the most vulnerable road users. Speed of vehicles is considered as one of the major causes of danger for pedestrians crossing the street (making cross movements). Therefore, it is of utmost importance to devise suitable solutions for reducing speed of vehicles. One of these solutions is installation of Pedestrian Refuge Islands (PRI) in very wide midblocks. With regard to fluctuations in pedestrian and vehicle traffic volume in traffic hours, there are different variations in collisions between vehicle and pedestrian. In this article the effect of constructed PRI in Tehran on speed of vehicles and consequently their effects on probability fluctuations of fatal accidents are determined. Speed of vehicles in two phases of before and after arriving to the PRI is assessed. Additionally, speed of vehicles in non-observed volumes of vehicle and pedestrian are calculated using Aimsun.v6 simulation software. Paired T-test is applied to compare average speed of vehicles before and after the PRI. The results revealed that except for traffic volumes of 3000-4000 veh/h and 400-600 ped/h in other volumes reduction of average speed of vehicles as a result of PRI is significant. Also, the results show that in all volumes, these equipments reduce the probability of fatal accidents to under 10%. According to the results, it is recommended that PRI should be installed in midblocks where traffic volume of vehicles in each lane is less than 750 veh/h.