## 2 State of the Art
### Level of Service LOS Definition
These numbers can be determined through on-site observations during peak traffic periods or through simulation using specific simulation software. In the case of the ramps, where the stairs have access to the views, as in the ramps of the Stari Most bridge, the LOS range must be set to allow space pedestrians stop to look at the view while allowing others to pass. The FHWA with the \"Pedestrian Facilities Users Guide\" in accordance with [39] recommends a walkway width of 1.5 m will comfortably allow two people to walk side by side. If space is provided for two walkers using the LOS D that means each person will have a walking buffer of 1.8 m by 0.75 m (1.4 m\({}^{2}\)) up to 2.93 m by 0.75 m (2.2 m\({}^{2}\)) for LOS D.  
This allows adequate room for stopping along the side of pedestrians pass single, the path to take pictures or enjoy the view action. Viswalk [40] was chosen as the most suitable tool for this comparison because well-developed specific algorithms derived from Social Force Model, Fruin Level of Service reporting based on density and analyzed data as described in Table 3 below. In accordance with [41] a pedestrian crosswalk walking speed was recommended considering a value of 1.2 m/s but a lower value is better if it is necessary to considering elderly pedestrians with a walking speed of 1.0 m/s [42]. Queuing areas are designed to allow walkers to comfortably wait for access to the use of a structure. Table 4 below shows the LOS FHWA criteria for queuing areas and stairs. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Stairs**} & \multicolumn{3}{c}{**Waiting Area**} \\ \cline{2-7}
**LOS** & **Space** & **Flow Rate** & **Average Speed** & **Average Speed** & **Space** & **Interspacing** \\  & **(m\({}^{2}\)/ped)** & **(ped/min/m)** & **Horiz. (m/min)** & **Horiz. (m/s)** & **(m\({}^{2}\)/ped)** & **Area (m)** \\ \hline \hline A & 1.9 & 16 & 32 & 0.53 & \(>\)1.21 & 1.2 \\ B & 1.6–1.9 & 16–20 & 32 & 0.53 & 0.93–1.21 & 0.9–1.2 \\ C & 1.1–1.6 & 20–26 & 29–32 & 0.48 & 0.65–0.93 & 0.7–0.9 \\ D & 0.7–1.1 & 26–36 & 25–29 & 0.42 & 0.27–0.65 & 0.3–0.7 \\ E & 0.5–0.7 & 36–49 & 24–25 & 0.4 & 0.19–0.27 & \(<\)0.3 \\ F & \(<\)0.5 & Var. & \(<\)24 & \(<\)0.40 & \(<\)0.19 & Negligible \\ \hline \hline \end{tabular}
\end{table} 
Table 4: LOS values considering stairs and waiting area. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Fruin Walkway LOS**} \\ \hline
**Ped/m/min** & **Ped/min/m** & **Ped/m\({}^{2}\)** & **Side Size (m)** & **Flow Condition** & \\ \hline A & \(<\)23 & \(<\)7 & 0.08 & 1.93–1.80 & Free flow & \\ B & 23.0–32.8 & 7–23 & 0.08–0.27 & 1.80–1.67 & Minor conflicts & \\ C & 32.8–48.2 & 23–33 & 0.27–0.45 & 1.67–1.52 & Slower speed & \\ D & 48.2–65.6 & 33–49 & 0.45–0.69 & 1.52–1.36 & Restricted most & \\ E & 65.6–82 & 49–82 & 0.69–1.66 & 1.36–1.18 & Restricted all & \\ F & \(>\)82 & \(>\)82 & \(>\)1.66 & 0.95–0.68 & Shuffling & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fruin Walkaway LOS. From a geometrical point of view, the criticalities linked to the evaluation of the LOS of Mostar bridge, derive from the difficulties measuring the widths of the two waiting areas and of the two ramps. The major geometric criticality is related to the usable width of the bridge. In general, the minimum width of 1.5 m allows two people to walk comfortably side by side. The sizing of the decks must also take into account the traveling speed. Moreover, for the design of ramps or stairs, more attention should be paid to the role of human characteristics due to the greater risks to safety and energy expenditure required by crossing them. The graph below linked to Figure 1, in accordance with [17] defines the value of LOS in ramps and stairs by comparing volume (P) defined as the volume in pedestrians per minute per foot of the stairway, with the module (M) in square feet area for pedestrian.