MBTA Healthy & Sustainable Transportation

Bus Only Lane in Boston

The MBTA’s expansive service and prominent regional position mean it has significant potential to alleviate congestion and mitigate greenhouse gas (GHG) emissions from single-occupancy vehicles through mode shift—trips taken on transit that may have otherwise been taken by car. Measures such as MBTA ridership provide context for mode shift, while GHG emissions reductions and bus electrification efforts work to advance healthy and sustainable transportation in the region. A new electricity procurement contract supplied by 100 percent renewable energy sources went into effect on January 1, 2021. This purchase has resulted in complete avoidance of the 36 percent of the MBTA’s GHG emissions that typically come from electricity usage during the second half of the fiscal year, and is likely a primary cause of decreased MBTA emissions from FY20 to FY21.

Ridership

Ridership measures the number of rides the MBTA system provides each year. In accordance with industry standard, ridership is measured as unlinked passenger trips (UPT), which reflect each time a passenger boards a transit vehicle. Unlinked passenger trips include estimates for trips that are not directly measured, such as behind-the-gate transfers and trips in which riders do not interact with the fare system. Ridership estimates for FY21 may be adjusted slightly in the future.

Riders completed a total of 119 million unlinked passenger trips across all MBTA services in FY21, or roughly 372,000 UPT on an average weekday. This represents a 57 percent decrease from 274 million UPT in FY20, and a 67 percent decrease from 363 million UPT in FY19, primarily due to the COVID-19 pandemic. Bus service retained the highest proportion of its ridership from FY20 to FY21 compared to other modes with a 42 percent decrease in ridership, followed by the RIDE with a 45 percent decrease in UPT. Ferry saw the greatest ridership decline of 87 percent from FY20 to FY21, followed by commuter rail with an 80 percent decrease. Heavy rail and light rail ridership decreased by 61 and 63 percent respectively from FY20 to FY21, but the Blue Line retained a relatively higher proportion of ridership with a 51 percent decline. Heavy rail, light rail, and bus ridership combined accounted for approximately 95 percent of system ridership in FY21.

Monthly Ridership

At the beginning of FY21, in July 2020, total ridership was around 27 percent of pre-pandemic ridership levels for the same month. By the end of FY21, in June 2021, ridership had increased to around 45 percent of pre-pandemic ridership for the same month. Bus ridership maintained a higher proportion of ridership through the fiscal year, at 44 percent of pre-pandemic levels in July 2020 and 58 percent by June 2021. Conversely, commuter rail ridership was around 10 percent of pre-pandemic levels in July 2020 and 28 percent by June 2021. In June 2021, roughly 53 percent of total trips were taken on subway (heavy and light rail), with 41 percent on bus, 5 percent on commuter rail, and 1 percent on ferry and the RIDE.

Monthly ridership estimates for FY21 may be adjusted slightly in the future. Monthly ridership may not match annual and monthly ridership estimates reported to the National Transit Database (NTD) due to new data that may become available after reports are submitted, such as from Green Line vehicles. The most current ridership estimates can be found on the MBTA Back on Track Dashboard.

Greenhouse Gas Emissions

Greenhouse gas (GHG) emissions are reported as the MBTA’s total GHG emissions in kilograms of carbon dioxide equivalent (kg CO2e) and as the rate normalized by total unlinked passenger trips (UPT). This measure does not account for GHG savings acquired via mode shift, from trips taken on transit rather than in single-occupancy vehicles, which is estimated to be at least four times larger than net emissions.

A new electricity procurement contract supplied by 100 percent renewable energy sources went into effect on January 1, 2021—as a result, the 36 percent of the MBTA’s GHG emissions that typically come from electricity usage have been avoided. In FY21, the MBTA emitted 287 million kg CO2e, a significant decrease from 355 million kg CO2e in FY20, likely due primarily to the renewable energy purchase. The Commonwealth of Massachusetts aims to reduce GHG emissions by 50 percent by 2050 compared to 2005 levels—the MBTA is on track to meet that goal. The rate of GHG emissions was 2.41 kg CO2e per UPT, an increase from 1.29 in FY20. This increase in the rate of GHG emissions despite the reduction in total emissions is largely due to the significant drop in unlinked passenger trips, the measure denominator, in FY21. Ridership estimates for FY21 may be adjusted slightly in the future.

Bus Fleet Composition

Bus fleet composition measures the proportions of the MBTA bus fleet that are electric or hybrid, or utilize compressed natural gas (CNG) or diesel fuel sources. Buses classified as electric include battery-electric buses and electric trolley buses, while buses classified as hybrid—with both electric and conventional fuel options—include traditional hybrid buses and Dual Mode Silver Line buses. In FY21, the MBTA’s roughly 1,300-bus fleet was 2.5 percent electric, 44.1 percent hybrid, 13.2 percent CNG, and 40.2 percent diesel.

Bus fleet composition particularly impacts residents living near bus routes due to criteria air pollutants emitted. While diesel-only buses emit higher levels of criteria air pollutants, alternative fuel buses (including electric, CNG, and hybrid) can mitigate air pollution caused by buses for nearby residents. Of residents living within a quarter mile of MBTA bus routes in FY21, roughly 49 percent were near routes running alternative fuel vehicles, 43 percent were near routes running vehicles of mixed fuel types, and 9 percent were near routes running diesel-only buses. Of low-income households within a quarter mile of MBTA bus routes, roughly 50 percent were near alternative fuel routes, and 8 percent were near diesel-only routes. And of residents of color living near MBTA bus routes, 45 percent were near alternative fuel routes and 8 percent were near diesel-only routes.