Level of service (LOS) is used as the main indicator of transport quality on urban roads and it is estimated based on the travel speed. The main objective of this study is to determine which of the existing models for travel INTRODUCTIONLOS is used as the main transport process quality indicator on urban streets. The input variable for LOS estimation on urban streets is travel speed which can be determined analytically or empirically. The speed is calculated using section's length and section travel time, depending on section and control delay. Intersection delays have the largest share in travel time and their assessment is the key step in determining LOS. In the process of speed estimation some analytical models directly take into account delays at intersections. Beside them, models describing travel speed and degree of saturation correlation, without taking into account signal timing parameters, are also present in literary sources.Since signalized arterials are subject of this analysis, travel time, and therefore travel speed will depend on control delay. This study is examining four models illustrating correlation between average speed and degree of saturation (HCM, Akcelik and Singapore model and Dowling-Skabardonis) in comparison to actual data gathered through survey on urban streets.In literary sources, the results obtained by model use are usually compared to actual data in an attempt to determine which better presents the particular conditions, or which better suits the particular type of urban street. That is the reason why Mtoi and Moses examined the use of different models for presenting the average travel speed and degree of saturation correlation for different street categories [1]. By comparing Akcelik model, modified BPR, modified Davidson and Conical function, it was concluded that Akcelik model provides the smallest RMSPE (Root Mean Square Percent Error) for signalized arterials in comparison to data gathered in the study. Ali, Venigalla and Flannery focused on travel time assessment, depending on street geometry and traffic parameters [2]. The authors developed a survey data based regression model and then compared the results from this model and HCM analytical procedure. They concluded that HCM underestimates the travel speed on smaller sections (<0.5 mile). The application of non-parametric Singapore model estimated the smallest RMSE in comparison to other models [3]. Results showed that this model can estimate the travel speed with deviation of 5 km/h in 95% of time. In their studies Dowling and Skabardonis compared BPR, exponential function and Akcelik model and concluded that all the applied functions and models provide good results for conditions below the saturation threshold [4]. However, the Akcelik model best illustrates the impact of degree of saturation on the speed, in comparison to presented functions in saturated conditions. Literature review recognizes models that can describe the current situation on a specific urban street type. This study further presents the sele...

Saturation flow is the base rate in the procedure for optimizing traffic signal operation and determining the measure for effectiveness of intersection operation. Different approaches and structures of analytical value models indicate the complexity of the problem of determining the saturation flow value in real conditions. This paper presents the synthesis of the results and conclusions of studying the saturation flow rate phenomenon at signalised intersections in Serbia in the last thirty years, by applying various survey techniques. The surveys relate to straight lane saturation flow value, in the survey conditions mostly resembling the idealised conditions in which saturation flow can be generated. The obtained results indicate that there is a significant trend of changes in the base saturation flow value compared with those first referred in 1963 by Webster and Cobbe, change in the significance of impact factor on saturation flow value, and the necessity to determine them on the local level.

Flashing green signal, as a part of the green traffic signal, indicates that the green signal is about to end. Drivers have more time to decide whether to stop or pass the intersection since they have prior information that the yellow signal will start. The application of flashing green at the end of the green signal is optional, hence, the question is how engineers could decide to use flashing green or not? The answer to the question should be based on researches on flashing green effects on traffic efficiency and safety at signalized intersections. The aim of this paper is to analyze the impact of flashing green on traffic efficiency by determining the value of effective green time. The research was conducted at two intersections in Belgrade, with and without a flashing green signal. Results indicate that effective green is shorter when flashing green is applied, due to the decreased utilization of the yellow signal.

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This paper presents the evaluation results of three traffic solutions for the complex grade-separated intersection located in the old part of Belgrade at the junction with the new bridge over the Sava River. The corridor to which the intersection belongs together with the new river bridge are parts of a great urban artery called the Inner Half Semi-Ring Road (IHSRR). The traffic solutions that are evaluated are defined in the preliminary design phase, based on two opposed concepts: a complete grade separation of all intersection legs (the CPV alternative Á 'grade-separated') and a grade separation designed to minimise construction costs (DMC 1 and 2 alternatives Á 'minimise cost'). The evaluation procedure is conducted in three steps: first, the score based on expert assessment of the functionality of the design solutions is determined; second, the alternatives are ranked according to the value of a set of state indicators obtained by microsimulation using PTVÁVISSIM 4.10; and third, the final score is obtained by multi-criteria evaluation using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method. The results of the first evaluation step show a small advantage for DMC 2, a sub-alternative of the DMC 1 alternative. The results of the micro-simulation give advantage to the DMC 1 alternative. The multi-criteria evaluation provides a better 'goodness factor' for the CPV alternative against the DMC 1 alternative. At the same time, the least construction cost favours alternative DMC 1.