Read for a continued explanation of the methodology the MBTA's Service Planning Department used to estimate the impacts on riders of the 47 Better Bus Project proposals affecting 63 bus routes. This post has three parts; this is part 3.
Outline
Part 1
Methodology Overview
- Estimating Passenger Travel Time Impacts
- Estimating Change in Frequency and Passenger Wait Times
Part 2
- Estimating Passenger Walk Time Impacts
- Estimating Passenger Transfer Time Impacts
- Estimating Stranded Passengers
- Estimating Impacts Across the Day
Part 3
- Estimating Ridership Impacts
- Combining All Time and Ridership Impacts to Calculate Net Impacts
Conclusion
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Part 3
7. Estimate Ridership Impacts
Once we have identified the travel, wait, or transfer impacts along with the number of riders estimated to experience these impacts, we use elasticities to estimate where new riders may be attracted or existing riders may be discouraged from using transit service, based on changes to travel time, frequency, or transfer time.
We also project ridership for proposals where we provide a new connection or serve a new service area. For instance, for the Route 64 proposal to extend all-day service to Kendall/MIT, we calculate the ratio of alightings between Central and Kendall (not including Central) to boardings between Oak Square and Central during the times when service to Kendall is provided (58%) and apply this percentage to the boarding count between Oak Square and Central during the times when service to Kendall is not provided (479). We estimate 278 (58% of 479) new riders on Route 64 because of the route extension.
8. Combine All Time and Ridership Impacts to Calculate Net Impacts
The final step is to sum time and ridership impacts to estimate the net change in passenger hours and passenger trips. For the Route 1/CT1 weekday proposal, we sum the travel time impacts, wait time impacts, and the walk time impacts across all trips to obtain the following values:
Impact TypeDescriptionPassenger CountSavings / Cost per Trip (minutes)Total Hours of Savings / CostTravel TimeRoute 1 riders boarding at Harvard minus those alighting around Harvard Square loop774-3-44.5Travel TimeRoute CT1 riders between Central and Harrison Ave1981374.8Wait TimeRoute 1 segments not shared with Route CT14423-1-92.9Wait TimeShared Route 1-Route CT1 segments883000.0Walk TimeRiders boarding and alighting around Harvard Square loop245Up to 619.0Walk TimeRiders boarding and alighting at Boston Medical Center327Up to 725.3Sum -18.8
From the elasticity calculations for travel time and headway improvements, we estimate 11 and 545 additional passenger trips, respectively, for a total of 556 new weekday passenger trips.
Conclusion
Each proposal to change a route is unique. The methodology used to estimate the impacts of these changes needs to capture these unique impacts but also summarize the results into comparable metrics across proposals. The estimates are complex and detailed, but they represent our best effort at accounting for the trade-offs that are inherent in every proposal so that an honest and informed discussion can be had to determine, in each case, if the benefits are worth the costs.
