## 2 State of the Art
### Level of Service LOS Definition  
Numerous studies are found in the literature that highlight the importance of the evaluation of LOS both for infrastructures crossed by only vehicles and/or vehicles and pedestrians. In accordance with [16], LOS values are very important especially on unprotected areas such as pedestrian crossings or footbridges. In addition, the need to consider people with disabilities has been identified for the evaluation of the specific LOS on the sidewalk and the crosswalk in mixed traffic conditions. The research highlights the importance of correlating the geometric conditions of the infrastructure with the type of users and their behavior in presence of other individuals. Many studies have been addressed on this topic and the increasingly comprehensive definition of the LOS parameters, as described in Table 1 below. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Period** & **Author** & **Parameters Correlated with LOS** \\ \hline
1971 & [PERSON] [17] & Human convenience and the design of environment. \\ \hline
1987 & [PERSON] and [PERSON] [18] & Pedestrian flow, speed and density relationship, and their \\  & & overtaking maneuvers. \\ \hline
1993 & [PERSON] [19] & Qualitative measures like safety, security, comfort and convenience, \\  & & continuity, system coherence and attractiveness. \\ \hline
1994 & [PERSON] [20] & Contribution of environmental factors towards service levels of pedestrians’ \\  & & facilities by adopting suitable performance measures. \\ \hline
2000 & HCM manual [21] & Analysis of pedestrian flow on sidewalks, crosswalks and street corners \\  & & mainly derived from [PERSON]’s research. \\ \hline
2001 & [PERSON] et al. [22] & Pedestrian perceptions of the quality of service. \\ \hline
2004 & [PERSON] et al. [23] & Total utility value of a facility based on sidewalk width and separation, \\  & & obstructions, flow rate andbicyclevevents. \\ \hline
2005 & [PERSON] et al. [24] & Path operations and found that the path width, the number of meeting and \\  & & passing events and the presence of a center line are the key variables in \\  & & determining in pedestrianperception \\ \hline
2006 & [PERSON] et al. [25] & Traffic volume, sidewalk’s adjacent roadway width and the density of \\  & & conflict points \\ \hline
2007 & [PERSON] et al. [26] & A sidewalk intercept survey to measure pedestrian perceptions of sidewalk \\  & & LOS and relative changing value \\  & & Relationship between pedestrians’ subjective perceptions, the quality of \\  & & physical facilities and the traffic flow operation \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Evaluation of LOS during the period 1971–2018. The value of the pedestrian LOS changes in accordance with the infrastructural details or spatial geometry. In fact, its value depends on the number of lanes or possible intersections that allow in both cases different trajectories [33] and presence of pedestrians on more rows or opposite directions [34]. Considering a network connection, the worst value predominates and the score is strongly influenced by the width of the walking area and its separation from the vehicles. Traffic volumes can also play an important role. On the other hand, if an intersection is considered, it is necessary to evaluate the level of service as a polynomial combination of the LOS due to the functionality and a LOS due to the connection. The final result also incorporates a delay factor of the road intersection. Finally, considering a pedestrian infrastructure, it is necessary to evaluate the correlation between vehicular and pedestrian space. Generally, the worst value predominates. The definition of the quality of an area for walking may depend on several different parameters such as the level of accessibility to the destination, the connectivity and the quality of the pedestrian network paths, safety etc.