3 Dropped Trips

Dropped trips is a measure of the percentage of bus trips that were not completed as scheduled. In 2015, the systemwide percentage of dropped trips was 1.9%, and 1.4% in 2016. Over the period 2015-16, this is an average of 1.7%. These values ranged considerably across individual bus routes, from a minimum of 0 to a maximum of 6.6%.

Route 111 experienced 6.1% dropped trips over the period 2015-16. Although Route 111 saw marked improvement in dropped trips between 2015 and 2016, its average across that time period still makes it the line with the second highest percentage of dropped trips across the MBTA system.

Table 3.1 below shows the 10 worst routes in terms of dropped trips for 2015, 2016, and averaged across the years 2015-16. Dropped trip data was provided by request from MBTA.

Table 3.1: 10 Worst Bus Routes by Percentage of Dropped Trips for 2015, 2016, and 2015-16.

Worst Routes 2015	Drop Trip % 2015	Worst Routes 2016	Drop Trip % 2016	Worst Routes 2015-16	Drop Trip % 2015-16
111	7.60	77	6.34	77	6.62
77	6.91	111	4.64	111	6.12
31	5.76	31	4.10	31	4.93
32	5.61	32	3.77	32	4.69
73	4.70	73	3.67	73	4.18
39	3.68	57	3.44	57	3.37
57	3.31	79	3.03	39	3.20
28	3.23	23	2.80	79	2.95
120 and 121	3.13	39	2.72	23	2.92
23	3.05	28	2.57	28	2.90

Figure 3.1 below is an interactive map of bus lines colored by perentage of dropped trips for 2015-16. Green shaded lines are above the systemwide dropped trip percentage, while red lines are below the systemwide dropped trip percentage. Hover your cursor over lines to see specific route numbers. Click on a line for more detail. Pan (click and drag) or zoom (+/-) on the map to explore.

Figure 3.1: Map of dropped trip percentages by bus route for 2015-16. Red lines indicate ontime percentages below systemwide percentage. Green are above systemwide ontime percentage.

3.1 Dropped Trips vs Demographics

3.1.1 Minority vs Dropped Trips

There is an apparent relationship between the percentage of minority riders of a bus route and the percentage of dropped trips. Figure 3.2 below is a scatter plot of percent minority of each bus route vs percent of dropped trips 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 percent dropped trips. In other words, the higher the percentage of minority riders on a bus route, the higher the percentage of dropped trips on that same route. Hover your cursor over individual points to see the Route number and dropped trip percentage.

Figure 3.2: Scatter plot of percent minority vs percent dropped trips. Red dot is Route 111.

There is a fairly consistent difference in dropped trips between minority lines and non-minority lines. Figure 3.3 below shows boxplots of the range of dropped trip percentages 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 percentage of dropped trips is higher for minority lines. In the aggregate, non-minority bus riders enjoy fewer dropped trips than minority bus riders.

Figure 3.3: Boxplots of bus route dropped trip percentages for minority and non-minority lines when the minority is defined by the state EJ threshold of 25% or MBTA threshold of 34.3%.

3.1.2 Low Income vs Dropped Trips

There is an apparent relationship between the percentage of low income riders of a bus route and the percentage of dropped trips, although it is less pronounced than for minority percenages. Figure 3.4 below is a scatterplot of percent low income of each bus route vs percent dropped trips 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 percent ontime. In other words, the higher the percentage of low income, the higher the percentage of dropped trips. Hover your cursor over individual points to see the Route number and ontime percentage.

Figure 3.4: Scatter plot of percent minority vs percent dropped trips. Red dot is Route 111.

There is a consistent difference in dropped trips between low income lines and non-low income lines. Figure 3.5 below shows boxplots of the range of dropped trip percentages 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. Similar to minority vs non-minority lines, the difference between low income and non-low income ontime performance is apparent either way, although the difference here is more apparent under the MBTA’s threshold. In the aggregate, non-low income bus riders enjoy a lower percentage of dropped trips than low income bus riders.

Figure 3.5: Boxplots of bus route dropped trip percentages for low income and non-low income lines when the low income line is defined by the threshold of 25% or MBTA threshold of 28.8%.

3.2 Dropped Trip Ratios

While there is a clear difference in dropped trip percentages for minority and low income riders, this difference does not exceed the MBTA’s threshold for determining disparate or dispropotionate impacts. 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.

Table 3.2 below shows ratios of dropped trip percentages between minority and non-minority lines and between minority lines and the systemwide ontime percentage. 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 1.2 or higher relative to the systemwide percentage. Although there is a consistent difference in performance, it does not exceed this 1.2 ratio threshold.

Table 3.2: Dropped trip percentages for minority and non-minority bus lines at different thresholds and ratios of minority to non-minority and minority to system dropped trip percentages.

Minority Threshold	Avg Minority Drop Trip %	Avg Non-Minority Drop Trip %	Ratio Minority/Non-Minority	Ratio Minority/System
25%	0.91	1.23	0.74	0.54
34.3%	1.03	0.93	1.11	0.61

In contrast to minority lines, there is an apparent disparate impact for low income lines and dropped trips. Table 3.3 below shows ratios of dropped trip percentages between low income and non-low income lines and between low income lines and the systemwide dropped trip percentage. Note that the ratio of low income to non-low income exceeds the 1.2 threshold, indicating a greater than 20% difference. However, the MBTA uses the ratio between low income and systemwide percentage to determine if there is a disparate impact. Under the latter, there is no apparent disparate impact.

Table 3.3: Dropped trip percentages for low income and non-low income bus lines at different thresholds and ratios of low income to non-low income and low income to system dropped trip percentages.

Low Inc Threshold	Avg Low Inc Drop Trip %	Avg Non-Low Inc Drop Trip %	Ratio Low Inc/Non-Low Inc	Ratio Low Inc/System
25%	1.06	0.80	1.32	0.62
28.8%	1.10	0.78	1.41	0.65