## 4 Research Methodology  
### Study Area Description  
Belgrade, the capital of Serbia, faces daily traffic jams due to rapid development and an increasing number of passenger cars, which number about 665,000, or about 400 per 1000 inhabitants [82]. In addition to traffic congestion, road traffic also affects excessively polluted air, which, according to the Annual Report on the State of Air Quality in Serbia [83], accounted for 41% of nitrogen oxide emissions, 10% of PM\({}_{10}\) emissions, and 9% of PM\({}_{2.5}\) emissions in 2021. Having the greatest impact on such statistics, Belgrade had excessively polluted air in the same period, mainly due to the increased concentration of particles PM\({}_{10}\), PM\({}_{2.5}\), and NO\({}_{2}\) from road traffic.  
According to the survey on the types of travel of individuals conducted in 2015 in Belgrade, the most common type of transport is public transport (47.9%), which consists of bus, trolleybus, and tram subsystems. This is followed by trips by private passenger cars (25.7%) and walking (23.8%), while only about 1% of residents travel by bicycle [84]. A small percentage of the use of bicycles in daily trips can be attributed to the bicycle infrastructure, which is not yet sufficiently developed in this city. The total length of bicycle paths is currently only 100 km. The Sustainable Urban Mobility Plan [85] adopted in 2020 considers the goals defined by the General Urban Plan of Belgrade (2016), which envisages the construction of a continuous bicycle network in the central city zone and central municipalities with a total length of more than 300 km, of which 100 km is already built by 2021. In addition to the realization of a continuous network in the central city zone and municipalities, the plan also foresees the construction of suburban bicycle corridors that would enable connection with suburban parts of the city. The development strategy of the city of Belgrade envisages the construction of 120 km of new bicycle paths, the provision of 200 parking spaces for bicycles, and the introduction of a public bicycle system by 2021 [86]. However, to date, those goals have not been fully achieved. The map of existing and planned bicycle paths is shown in Figure 1.  
\begin{table}
\begin{tabular}{c c c} \hline
**Criterion** & **Multilayer Perceptron (MLP)** & **Radial Basis Function (RBF)** \\ \hline Advantages & Can learn complex, nonlinear relations & Fast training, good for simple tasks \\ \hline Disadvantages & Slow to train, requires more data & Less flexible, may underfit complex tasks \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 1: Map of the existing and planned bike paths [87].  
In terms of topography, Belgrade is situated on low-land and hilly terrain. The highest altitude above sea level of the wider area of Belgrade amounts to 628 m, while the highest altitude in the central city area amounts to 303 m. The lowest altitude in the city is 70 m. The absolute altitude of the Meteorological Observatory--132 m--is considered to be the average altitude of Belgrade.  
Also, for the purposes of this work, it is important to point out the fact that the current legislation in Serbia recognizes an electric bicycle as a traditional bicycle without an electric drive, with a maximum power not exceeding 250 W, and with a maximum design speed of 25 km. Regarding their participation in traffic, users of e-bikes are obliged to move on the bicycle infrastructure (lanes and paths), as well as on the roadway with a width of at most one meter from the right edge, only if the bicycle infrastructure does not exist. As Belgrade does not have a developed common system of e-bikes, a trip by e-bike is most often achieved with its own resources. Also, the state has so far not provided additional subsidies and incentives for the purchase of these electric vehicles.