4 Overcrowding
Overcrowding is measured by the amount of time bus passengers spend in crowded conditions. According to the MBTA Office of Performance Management and Innovation, all passengers are counted as crowded during peak hours if the bus is at 140% of seated capacity. During nonpeak hours, 125% of seated capacity is crowded. See http://www.mbtabackontrack.com/blog/60-bus-crowding-introduction for more information on how crowding was measured. Overcrowding data was provided by request from MBTA.
MBTA judges a route by the percentage of passenger minutes on that route that are comfortable (i.e. not crowded). This is reported as a “comfort fraction”: percent of time passengers spent in non-crowded conditions. A comfort fraction of less than 95% is considered to be failing MBTA’s proposed standard. In 2015, the systemwide comfort fraction was 95.6%. In 2017, it worsened slightly to 95.2%. For 2015 and 2017, the combined systemwide comfort fraction was 95.4%. The comfort fraction varied by day type; lower during weekdays and higher during weekends and holidays. Table 4.1 below summarizes the comfort fraction by year and day type.
| Year | Holidays | Saturdays | Sundays | Weekdays |
|---|---|---|---|---|
| 2015 | 97.3 | 97.4 | 97.3 | 94.1 |
| 2017 | 98.3 | 96.8 | 96.6 | 93.5 |
| 2015-17 | 97.7 | 97.1 | 97.0 | 93.8 |
There is considerable variation in comfort fraction between bus routes. In 2015, the comfort fraction ranged from a low of 81.8% to a high of 100%. In 2017, the minimum worsened to 80.6%. This means that in 2015, 22 bus lines failed to meet MBTA’s 95% comfort fraction standard. In 2017, 24 bus lines did not meet the standard. The number of lines not meeting the 95% standard is higher during weekdays. Route 111 has been among the most overcrowded lines. In 2015, its comfort fraction was 85.8% (4th most overcrowded) and worsened to 83.6% (3rd most overcrowded) in 2017. Table 4.2 below shows the 10 worst performing lines for 2015, 2017, and averaged across 2015-17.
| Worst Routes 2015 | CF 2015 | Worst Routes 2017 | CF 2017 | Worst Routes 2015-17 | CF 2015-17 |
|---|---|---|---|---|---|
| 7 | 81.8 | 65 | 80.6 | 65 | 81.9 |
| 65 | 83.2 | 7 | 83.6 | 7 | 82.6 |
| 109 | 85.3 | 111 | 83.6 | 111 | 84.8 |
| 111 | 85.8 | 1 | 84.0 | 109 | 85.2 |
| 9 | 90.1 | 109 | 85.1 | 1 | 88.3 |
| 57+57A | 90.7 | 62 | 89.9 | 9 | 90.1 |
| 104 | 90.8 | 9 | 90.1 | 62 | 90.4 |
| 62 | 90.8 | 104 | 91.5 | 104 | 91.1 |
| 34+34E | 90.9 | 57+57A | 91.9 | 57+57A | 91.2 |
| 47 | 92.4 | 501 | 92.3 | 501 | 92.5 |
Figure 4.1 below is an interactive map of bus lines colored by comfort fraction. Green shaded lines are above the systemwide comfort fraction for 2015-17, while red lines are below the systemwide comfort fraction. Hover your cursor over lines to see specific route numbers. Click on a line for more detail and to bring that line forward. Pan (click and drag) or zoom (+/-) on the map to explore.
Figure 4.1: Map of comfort fraction by bus route for 2015-17.
4.1 Overcrowding vs Demographics
4.1.1 Minority vs Overcrowding
There is an apparent relationship between the percentage of minority riders of a bus route and the comfort fraction (i.e. fraction of time that bus route is not overcrowded). Figure 4.2 below is a scatter plot of percent minority of each bus route vs comfort fraction of the same bus routes. The blue line is a linear trend line. The slighly positive slope of the trend line suggests a positive relationship between percent minority and comfort fraction. In other words, the higher the percentage of minority riders on a bus route, the higher the comfort fraction (less overcrowded) of that same route. Hover your cursor over individual points to see the Route number and dropped trip percentage.
Figure 4.2: Scatter plot of percent minority vs comfort fraction. Red dot is Route 111.
There is a difference in comfort fraction between minority lines and non-minority lines. Except for notable outliers, minority lines are generally less overcrowded (i.e have a higher comfort fraction) than non-minority lines. Figure 4.3 below shows boxplots of the range of comfort fractions for all minority routes and for all non-minority routes using different minority thresholds. Because the definition of what constitutes a “minority” line is debatable, the boxplots show the impact of choosing the MBTA’s systemwide percentage threshold for defining a minority line versus the states’s EJ policy threshold. In either case, the median comfort fraction is higher for minority lines.
Figure 4.3: Boxplots of bus route comfort fractions for minority and non-minority lines when the minority is defined by the state EJ threshold of 25% or MBTA threshold of 34.3%.
4.1.2 Low Income vs Overcrowding
There is an apparent relationship between the percentage of low income riders of a bus route and the comfort fraction (i.e. fraction of time that bus route is not overcrowded). Figure 4.4 below is a scatter plot of percent low income of each bus route vs comfort fraction of the same bus routes. The blue line is a linear trend line. The slighly positive slope of the trend line suggests a positive relationship between percent low income and comfort fraction. In other words, the higher the percentage of low income riders on a bus route, the higher the comfort fraction (less overcrowded) of that same route. Hover your cursor over individual points to see the Route number and dropped trip percentage.
Figure 4.4: Scatter plot of percent low income vs comfort fraction. Red dot is Route 111.
There is a difference in comfort fraction between low income lines and non-low income lines. Except for notable outliers, low income lines are less overcrowded (i.e have a higher comfort fraction) than non-low income lines. Figure 4.5 below shows boxplots of the range of comfort fractions for all low income routes and for all non-low income routes using different low income thresholds. Because the definition of what constitutes a “low income” line is debatable, the boxplots show the impact of choosing the MBTA’s systemwide percentage threshold for defining a low income line versus the states’s EJ policy threshold. In either case, the median comfort fraction is higher for low income lines.
Figure 4.5: Boxplots of bus route comfort fractions for low income and non-low income lines when low income is defined by the state EJ threshold of 25% or MBTA threshold of 28.8%.
4.2 Comfort Fraction Ratios
As indicated above, differences in comfort fraction appear to favor minority lines. The MBTA uses a 20-percent threshold for identifying potential disparate impacts for service monitoring. In other words, a disparate or disproportionate impact exists only when there is a 20-percent or greater difference in service, amenities, or impacts between minority or low income riders and non-minority or non-low income riders.
Minority lines exhibit comfort fractions exceeding those of non-minority lines. Table 4.3 below shows ratios of comfort fractions between minority and non-minority lines and between minority lines and the systemwide comfort fraction. Only the latter ratio is used by the MBTA to determine whether a disparate impact exists. For a disparate impact to exist according to the MBTA, minority lines would need to have a ratio of 0.8 or lower relative to the systemwide comfort fraction.
| Minority Threshold | Minority CF | Non-Minority CF | Ratio Minority/Non-Minority | Ratio Minority/System |
|---|---|---|---|---|
| 25% | 95.559 | 94.985 | 1.006 | 100.167 |
| 34.3% | 95.583 | 95.259 | 1.003 | 100.192 |
Low income lines appear to be no different than non-low income lines in terms of their comfort fraction. Table 4.4 below shows ratios of comfort fractions between low income and non-low income lines and between low income lines and the systemwide comfort fraction. Only the latter ratio is used by the MBTA to determine whether a disparate impact exists. For a disparate impact to exist according to the MBTA, low income lines would need to have a ratio of 0.8 or lower relative to the systemwide comfort fraction.
| Low Income Threshold | Low Income CF | Non-Low Income CF | Ratio Low Income/Non-Low Income | Ratio Low Income/System |
|---|---|---|---|---|
| 25% | 95.524 | 95.506 | 1.000 | 100.130 |
| 28.8% | 95.456 | 95.828 | 0.996 | 100.059 |