## 4 Evaluating the Effect of the Maze Meltdown
### Effect on BART  
The level of urbanization markedly varies within the region, potentially affecting the level of BART utilization [22]. The Richmond, Concord, San Rafael, and Hayward areas are primarily residential areas, while the San Francisco, Oakland, and San Jose areas (see Figure 1a) are primarily central business districts that include some residential areas. Commuters from the Richmond, Concord, and Oakland to San Francisco downtown areas were directly impacted due to the freeway collapse. A marked increase in BART ridership was observed at many stations following the incident. BART's average weekday ridership is 340,000. BART set its single day record of 375,200 passengers on Tuesday, 1 May 2007. Many of those who rode BART that day were attempting to avoid the complications caused by the Maze Meltdown freeway repairs. The third highest total in BART's history occurred two days later on Thursday, 3 May when 374,200 passengers used BART [23]. The white circles shown in Figure 2a indicate the locations of the 44 BART stations. Daily BART ridership ranges from 314,500 to 354,000 on weekdays, and 102,000 to 168,000 on weekends. The data from West Dublin (see station 22 in Figure 3b) were not available and not included in the analysis. The hourly ridership of BART did not significantly deviate from normal demand during the freeway repairs. Figure 2b-d show hourly BART ridership (represented by the solid black line) at different phases (see Figure 1d) compared with that of N1 (represented by the light grey line) at El Cerrito Plaza station (see station 37 in Figure 2a). Hourly BART ridership during R1 remained within the 95% confidence interval (CI) of the hourly ridership observed during N1. Hourly BART demand during R2 and N2 also remained within 95%. If hourly ridership had varied greatly during the recovery period, utilization of different timetabling strategies and additional trains might have been considered [24]. However, it appears that BART could accommodate the additional demand shifted from the freeway without temporarily increasing the trains' existing capacity. Although the hourly demand observed during different stages of recovery period did not deviate significantly from pre-incident demand, the total daily ridership was significantly increased during R1. Figure 2e shows the distribution of BART ridership observed at El Cerrito Plaza during weekdays. The solid black line, P\({}_{\text{N1}}\)(t), shows the empirical probability distribution of daily demand observed at El Cerrito Plaza station. The white circle, triangle, and cross in the figure are the observed average demand at El Cerrito Plaza station during R1, R2, and N2 periods, respectively. Figure 2: _Cont._  
How much the ridership changed compared to the N1 period can be quantified by the \(p\)-value of the average demand estimated using P\({}_{\text{N1}}\)(t): a \(p\)-value less than 0.05 indicates an increase in demand that is higher than the 99.5 percentile of demand observed during N1. The \(p\)-value of the average daily ridership observed during R1 was 0.00002 (represented by the white circle in Figure 2e) indicating a significant increase in BART ridership. This increase in ridership declined as the connectors were sequentially reopened. The \(p\)-values of daily ridership during R2, after the reopening of the I-80W to I-880S connector (see arrow 2 in Figure 1b) and N2, after reopening of the SFOBB to I-580E connector (see arrow 4 in Figure 1b), were 0.11 and 0.23, respectively (see the triangle and cross in Figure 2e). The demand observed during R2 and N2 at El Cerrito Plaza station was within 89 percentile of the demand observed during N1. A similar pattern was observed at a number of other stations, as is shown in Figure 3.  
Figure 3a shows the histogram of stations with respect to different \(p\)-values of average weekday BART ridership based on the station entry data: P\({}_{\text{N1}}\)(t) at each station was used in estimating the \(p\)-value of average ridership during R1, R2, and N2.