## 2 State of the Art
### Level of Service LOS Definition
Various definitions of service level have been developed by different researchers as far as possible to find LOS A defined as \"best\", \"safer\", \"very satisfied\" or \"excellent\" in several studies. According to [35; 36] six levels of services were considered for pedestrian structures (walkways, stairwells and tails) based on the occupation of the middle area (density) and flow. The Fruin standard was determined on the basis of walking speed, pedestrian spacing and the likelihood of conflict at various traffic concentrations. It was corrected by the National Cooperative Highway Research Program in 2008 and was reported on the [37]. In this standard, the breakpoints between the levels are set to lower values than the Fruin standard such as that described in Table 2.  
Pedestrians travel time after time in the spaces, not only is linked to a single way condition, but also to the over cross action in different space type. The platooning configuration often occurs when people move in a group forming a queue. This scenario is also analyzed by the HCM manual classifying it as an event in general of a lower level than that determined by the average pedestrian flow. The pedestrian unit flow rate (ped/min/m) is obtained by taking the pedestrian 15-min flow rate (ped/15-min) and dividing by the effective walkway width. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Period** & **Author** & \multicolumn{4}{c}{**Parameters Correlated with LOS**} \\ \hline \multirow{3}{*}{2008} & [PERSON] and [PERSON] [28] & LOS related to the physical parameters like sidewalk width, sidewalk surface, & & & \\  & [PERSON] and & & & & & \\  & [PERSON] [29] & & & & & \\ \hline \multirow{3}{*}{2010} & [PERSON] et al. [30] & They consider the pedestrian movements along the carriageway & & & \\  & & & & & (on or at side) and on a pedestrian facility & \\ \hline \multirow{3}{*}{2014} & [PERSON], et al. [31] & Pedestrian movements along the carriageway (on or at side) and on a pedestrian facility & & & \\  & & & & pedestrian facility & & \\ \hline \multirow{3}{*}{2018} & [PERSON] et al. [32] & Modeling human comfort perception in the evaluation of pedestrian & & & \\  & & & behavior patterns & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._ \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{5}{c}{**Level of Service LOS**} \\ \hline \multirow{2}{*}{} & A & B & C & D & E & \\ \cline{2-6}  & & & & & **FRUIN** & \\ \hline \multirow{2}{*}{**Period (1971)**} & \multirow{2}{*}{\(>\)3.20} & \multirow{2}{*}{2.3-3.2} & \multirow{2}{*}{1.4–2.3} & \multirow{2}{*}{0.9–1.4} & \multirow{2}{*}{0.5–0.9} & \multirow{2}{*}{\(<\)0.5} \\  & & & & & & \\ \cline{1-1} \cline{5-6}  & & & & & & \\ \cline{1-1} \cline{5-6}  & & & & & & \\ \hline \multirow{2}{*}{**Period (2000)**} & \multicolumn{5}{c}{**HCM**} \\ \cline{2-6}  & & & & & & \\ \cline{1-1} \cline{5-6}  & & & & & & \\ \cline{1-1} \cline{5-6}  & & & & & & \\ \cline{1-1} \cline{5-6}  & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Level of Service value comparison. The HCM suggests collecting pedestrian opposing flow volumes at 15-min intervals. The sum of the two directional flows is used as the 15-min flow rate. The obstacle widths can be measured from the field. The additional buffer width is based on an estimation provided by the HCM. A speed reduction of 0.1 m/s is used on grades greater than 10 per cent (1:10 slopes) and on stairs. In the accumulation areas (defined in the present study, simply Wed E areas), especially in the historical center, it often appears that people and visitors are intolerant to LOS E and F because of the queuing areas. The queuing areas should be designed with a value of LOS D as the minimum area per pedestrian. These levels should be confirmed through on-site perception studies according to [38]. Unfortunately, in the literature there are no indications on the number of pedestrians that should be accommodated.