## 5 Deterioration Features and Data Description of the Tokyo Region
### Data Arrangement and Description
\begin{table}
\begin{tabular}{c c} \hline \hline  & **Name of Variable** & **Unit/Code** \\ \hline Objective variable & Bridge age & Year \\ \cline{2-3}  & Event & 1 = two-dimensional cracks and the appearance \\  & & of efflorescence at the bottom of the slab \\ \hline  & Number of vehicles & Unit: Vehicles per day (whole cross-section) \\  & & Mean: 44,961.71 \\  & & Standard deviation: 11,528.41 \\ \cline{2-3}  & & Unit: m \\  & Span length & Mean: 35.00 \\  & & Standard deviation: 9.69 \\ \cline{2-3}  & & Unit: cm \\  & & Mean: 19.79 \\  & & Standard deviation: 2.04 \\ \cline{2-3}  & & Unit: mm per season \\  & & Average precipitation from December to February \\  & & Mean: 158.04 \\  & & Standard deviation: 5.70 \\ \cline{2-3}  & & Slope & Mean: 1.51\% \\  & & Standard deviation: 1.38\% \\ \hline  & \multirow{2}{*}{Categorical covariates} & \multirow{2}{*}{Crossing condition} & River: crossing over river and pond \\  & & Overpass: crossing roads and railways \\ \cline{2-3}  & & Edge & Yes: the panel is near the expansion joint \\  & & No: the panel is not near the expansion joint \\ \cline{2-3}  & & Girder type & Simple: simple girder \\  & & Continuous: continuous girder \\ \cline{2-3}  & & Design code & Before S39: S31 and S39 \\  & & After S39: S48, S55, etc. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Variables used in analysis in Tokyo region. Variables used in the analysis are shown in Table 5. As for East Japan, the mean value and standard deviation of numeric covariates and detailed definitions of category covariates are also shown. The selection process was the same as for East Japan. The National Land Numerical Information published by MLIT was used for weather data accumulation. As already stated, the bridges of these two regions are governed by different organizations; therefore, the inspection systems are different. East Japan bridge inspection mainly focuses on water leakage and efflorescence. However, Tokyo region bridge inspection not only focuses on efflorescence, it also pays attention to crack density. Therefore, some variables in the dataset were different than for the East Japan dataset. Traffic volume, structural features, panel position, design code, and precipitation were used as variables. Design codes were divided into two groups: the first for design codes from 1964 and 1956, and the second for those after 1964 (1973, 1980, etc.). The reason for this division is that major reforms in mechanical resistance specifications occurred after 1964. Table 6 compares the minimum ratio for the distributing bar and slab thickness between different design standards. It can be clearly seen that the amount of the distributing bar specified increased after 1964. Additionally, the minimum slab thickness increased after 1973. Currently, judgment of the cause of deterioration depends on bridge engineers' experience and skills. However, visual inspection and sound testing are inefficient and rely too much on inspectors' personal judgment. In many cases, it was difficult to identify a single factor responsible for deterioration. In such cases, deterioration was simply recorded in the inspection ledger as 'complex deterioration with multiple deterioration factors'. This method would not contribute to efficient maintenance based on the structural and environmental conditions of individual bridges. Thus, identifying predominant risk factors is urgently necessary.