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Behind the scenes with MBTA data.

Read the below for an 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 2.

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

For more on the Better Bus Project and to learn how you can give feedback, see our project page.

Walk time impacts are estimated for riders at the stops that are no longer served because of the proposal. We used Google to calculate walk times from the eliminated stop to the nearest remaining stop. For example, in the Route 1 proposal to eliminate service around Harvard Square, we obtained a walk time of 4 minutes from the stop at Quincy Street at Broadway opposite Fogg Museum to Massachusetts Avenue at Holyoke Street. Walk times are calculated for distances up to a half-mile where sidewalks or other pedestrian facilities are available. 

Walk directions from potentially eliminated stop to replacement stop

We consider a transfer impact when a stop is eliminated from one route’s service but is served by other routes. We assume that riders could take another route to make the same trip, but only if the remaining route structure and riders’ destinations are compatible.

Sometimes the remaining service does not share stops or connect to other routes that serve the same areas as the current service might.  In those cases, we do not assume that riders will be diverted.  For example, the proposal to operate the portion of Route 411 between Kennedy Drive and the Jack Satter House only in the midday leaves existing Route 411 riders in eastern Revere without even a two-seat ride to get to Salem Street or Malden Station. This portion of Route 411 is walkable from several other routes, but riders are not expected to divert to make the same trips. The only portion of Route 411 that is considered for rider diversion is at stops shared with or near Route 119 or Route 426, since these routes travel to Linden Square where a rider could transfer to Route 108 to Salem Street or Malden Station. 

Map showing proposed service changes on route 411

In the proposal for Route 89, which eliminates the variation to Clarendon Hill, we assume that the riders along this section travel to/from Broadway. While some riders along the eliminated section can walk to Broadway and pick up the remaining service, riders beyond a half-mile of Broadway are assumed to take Route 87 or Route 88 to Davis Station and then transfer to Route 89.

Map showing proposed changes on route 89

In the cases where a destination can be assumed, the transfer time comprises several factors: wait time for the remaining route or routes, travel time to the transfer point, and wait time for the revised route. In the Route 89 proposal, the transfer time for riders along the eliminated section of Broadway beyond a half-mile from the revised route is one-half the combined headway for Routes 87 and 88 plus the travel time to Davis Station plus one-half the headway for Route 89. The net transfer time impact is the difference between the transfer time and one-half the former Route 89 headway at Clarendon Hill.

"Stranded" passengers are defined as any passengers who board or exit at a stop today, but will be beyond a half-mile from service if a proposal is put in place. For example, for Route 411, this counts riders who board or exit the bus between Jack Satter House and Bell Circle (on the East side of the map above).  For Route 89, there are no stranded riders because all remaining riders can walk or use Routes 87 or 88 to access Route 89.

We used the methodologies described above to estimate the per-trip change in travel, wait, walk and transfer times. The next step is to estimate these changes across the day. The level of time aggregation varies by the metric. For travel time, our APC query summarizes data by hour. Walk times are assumed to be consistent across the entire day. For wait and transfer times, we summarize into the following time periods:

  • Early AM: before 7:00 AM
  • AM Peak: 7:00 AM to 9:00 AM
  • Midday: 9:00 AM to 4:00 PM
  • PM Peak: 4:00 PM to 6:30 PM
  • Evening: after 6:30 PM

Using the changes in components of passenger travel time, we apply each portion to the count of riders who would experience that change, as identified from our APC ridership counts by stop.  Below is an example of the data presented for an inbound 7:16 AM trip on Route 1 from our 2017 data.

Estimating total ridership changes along route from all changes

The proposal for Route 1 omits the loop around Harvard Square and instead turns left on Dunster Street. The proposal also consolidates Routes 1 and CT1 into a single Route 1.

So, for the example 7:16 AM inbound Route 1 trip, the count of riders with a travel time impact is the sum of ons at Massachusetts Avenue at Holyoke Street and Massachusetts Avenue at Johnston Gate, or 7.1 passengers, minus the sum of offs along Quincy St, or 0.1 passengers, for a total 7.0 passengers.  We assume that passengers boarding at Johnston Gate receive the travel time benefit but passengers boarding along Quincy St. do not receive the travel time benefit because they are at the end of the loop.

Regarding wait time, there are two groups of riders with different impacts—those served by both Route 1/Route CT1 and those served only by Route 1. For riders served by both Route 1/Route CT1, the wait time change is one half the difference of the combined effective Route 1/CT1 headway and the new Route 1 headway. For the riders at stops served only by Route 1, their wait time change is one half the difference between the Route 1 headway based on 90th-percentile cycle times and the new Route 1 headway with the added reinvestment from Route CT1. Note that we only consider boardings so that we count the number of riders being impacted once.

Walk time is calculated for the three stops around Harvard Square – 3 minutes, 6 minutes, and 2 minutes, at Johnston Gate and the Quincy St stops, respectively – and applied to the ridership at these stops. Walk time is calculated for both boardings and alightings because it reflects the additional walk time passengers would incur on either end.

Transfer time impact does not apply for the Route 1/CT1 proposal, so we will use a different example.  First, we identify stops where riders would divert onto other service. Then the impact is applied to either boardings, alightings or both depending on the direction of travel. For example, in the Route 89 proposal to eliminate service to Clarendon Hill, the transfer impact is only calculated for inbound boardings and outbound alightings along the eliminated section. The impact for inbound alightings or outbound boardings along this section is already captured by the walk time impact calculation.

The following table summarizes the count of riders, their time savings/cost, and the total number of minutes saved/cost for all affected passengers by impact type for the Route 1 example trip above.  Negative numbers represent a savings, and positive numbers represent a cost. With travel time savings of 35.7 minutes, wait time savings of 31.4 minutes, and walk time cost of 19.5 minutes, the net passenger-time impact is a savings of 47.6 minutes for this trip.

Impact Type Description Passenger Count Savings / Cost per Trip (minutes) Total Minutes Savings / Cost
Travel Time Riders boarding at Harvard minus those alighting around Harvard Square loop 7.0 -5.1 -35.7
Wait Time Route 1 segments not shared with Route CT1 20.9 -1.5 -31.4
Wait Time Route 1 segments shared with Route CT1 45.1 0.0 0.0
Walk Time Riders boarding and alighting around Harvard Square loop 5.3 Varies by Stop 19.5
Sum       -47.6

We estimate the aggregate daily passenger-time change by summing the impacts and riders affected by these impacts for each trip. In our proposal summaries, we also estimate the time impacts by impact type. Since the time impacts vary by trip depending on time of day, we typically provide the median value in the summary document. 

Next: the final post in this series, discussing how we put everything together to estimate the impacts on ridership.

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.

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

For more on the Better Bus Project and to learn how you can give feedback, see our project page.

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.

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 Type Description Passenger Count Savings / Cost per Trip (minutes) Total Hours of Savings / Cost
Travel Time Route 1 riders boarding at Harvard minus those alighting around Harvard Square loop 774 -3 -44.5
Travel Time Route CT1 riders between Central and Harrison Ave 1981 3 74.8
Wait Time Route 1 segments not shared with Route CT1 4423 -1 -92.9
Wait Time Shared Route 1-Route CT1 segments 8830 0 0.0
Walk Time Riders boarding and alighting around Harvard Square loop 245 Up to 6 19.0
Walk Time Riders boarding and alighting at Boston Medical Center 327 Up to 7 25.3
Sum       -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.