CTPS
CENTRAL TRANSPORTATION PLANNING STAFF
Staff to the Boston Region Metropolitan Planning Organization
CENTRAL TRANSPORTATION
PLANNING STAFF
TECHNICAL MEMORANDUM
DATE: July 25, 2014
TO:
David Mohler, Executive Director, Office of Transportation Planning
(MassDOT)
FROM: Ben Dowling, Central Transportation Planning Staff (CTPS)
RE:
Air-Quality Interim Offset Measures Results and Methodology
This memorandum presents the results of air-quality interim offset measures
(interim offsets) in compliance with the State Implementation Plan (SIP),
Transportation Control Measures (TCM), and the methodologies employed to
estimate interim offset measures.
1.
BACKGROUND
The Green Line Extension (GLX) is one of the outstanding TCM commitments
currently listed in the SIP. According to title 310 CMR 7.36, the Commonwealth
requires this project to be built by December 31, 2014 as an air-quality mitigation
measure for the Central Artery/Third Harbor Tunnel (CA/T) project. Construction
must be complete and operations must have commenced on the GLX’s two
branches—between Lechmere Station and Medford Hillside, and between
Lechmere Station and Union Square—by this date in order to meet this legal
deadline. However, given the complexity of the project and the length of time
required for construction, the Massachusetts Department of Transportation
(MassDOT) currently estimates that the Green Line Extension project may not be
completed until 2018 to 2020.
A provision of 320 CMR 7.36 allows for TCM project delays if interim offset
measures are implemented that result in emission reductions in non-methane
hydrocarbons (NMHC) carbon monoxide (CO), and nitrogen oxides (NOx) equal
to or greater than the emission reductions that would have been achieved had
the required GLX project not been delayed. Volatile organic compounds (VOC)
have traditionally been deemed to be equivalent to NMHC.
The MBTA and previously MassDOT, in consultation with CTPS, developed a list
of projects, programs, and measures for interim offsets; and through a process of
testing, have identified a suite of interim offsets that realize air-quality
improvements, which in 2015, would be greater than what would be achieved by
constructing the GLX.
State Transportation Building • Ten Park Plaza, Suite 2150 • Boston, MA 02116-3968 • (617) 973-7100 • Fax (617) 973-8855 • TTY (617) 973-7089 • ctps@ctps.org
Air-Quality Interim Offset Measures Results and Methodology
July 25, 2014
FIGURE 1
Boston Metropolitan Planning Organization Region
1.1
The GLX Emissions “Budget”
Before testing interim offset measures, the emissions reductions associated with
constructing the GLX alone were established for the forecast year 2015, which is
when the GLX originally was scheduled to begin service. The emissions
reductions were estimated for the Boston Metropolitan Planning Organization
(MPO) region of 101 cities and towns (shown in Figure 1 above).The CTPS travel
demand forecast model and spreadsheet tools were used to estimate air-quality
benefits that would be realized from auto diversions resulting from construction of
the GLX. Based on an analysis from November 2011, the GLX should result in
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Air-Quality Interim Offset Measures Results and Methodology
July 25, 2014
an average daily reduction in 46,500 vehicle-miles traveled (VMT) in the Boston
MPO region, which translates to a GLX “budget” of 13.5 kilograms (kg) of VOC,
22.4 kg of NO x , and 459.2 kg of CO. The stationary source emissions that would
be produced by additional Green Line service were not subtracted from the
budget.
1.2
Interim Offset Measures
In collaboration with CTPS, MassDOT has identified the following measures
whose emissions savings collectively would exceed the savings anticipated from
completion of the GLX project.
1. Twenty percent increase in off-peak vehicle trips per hour for all Green
Line services
2. Twenty percent increase in off-peak vehicle trips per hour for MBTA bus
routes 80, 88, 91, 94, and 96
3. Purchase of 142 Ford Fusion Hybrid vehicles for MBTA THE RIDE service
to replace older Crown Victoria vehicles
4. Addition of 374 parking spaces at the Salem commuter rail parking garage
and 378 more parking spaces at the Beverly commuter rail parking garage
Off-Peak Green Line and Bus Schedules
A twenty percent increase in off-peak vehicle trips per hour on an average
weekday is proposed for all Green Line branches, B, C, D, and E, between 9:00
AM and 3:00 PM and between 6:00 PM and 6:00 AM—Tuesday, Wednesday,
and Thursday qualify as average weekdays. (Extended late-night weekend
service was not included in this analysis.) A twenty percent increase in the
number of vehicle trips per hour also is proposed for five MBTA bus routes,
Routes 80, 88, 91, 94 and 96, during the same average weekday off-peak
periods. More frequent transit service would cause a mode shift from auto to
transit, which in turn would result in air-quality improvement. Table 1 below
displays what the potential change would look like in terms of improved
headways (minutes) for the Green Line; and Table 2 presents the potential
improvement in weekday off-peak bus headways.
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TABLE 1
Existing and Proposed Headways (Minutes) for Green Line Branches
Green Line Branch
Green Line B Branch between Boston
College and Government Center
Green Line C Branch between
Cleveland Circle and North Station
Green Line D Branch between
Riverside and Government Center
Green Line E Branch between Heath
Street Lechmere Station
Existing
Midday
Service
Headways
Proposed
Midday
Service
Headways
Existing
Night time
Service
Headways
Proposed
Night time
Service
Headways
9.0
7.5
10.0
8.3
10.0
8.3
7.0
5.8
11.0
9.2
10.0
8.3
8.0
6.7
10.0
8.3
TABLE 2
Existing and Proposed Headways (Minutes) for MBTA Bus Routes
Route
Route 80 between Arlington Center
and Lechmere Station−Inbound
Route 80 between Arlington Center
and Lechmere Station−Outbound
Route 88 between Clarendon Hill and
Lechmere Station−Inbound
Route 88 between Clarendon Hill and
Lechmere Station−Outbound
Route 91 between Sullivan Square
Station and Central Square
Cambridge−Inbound
Route 91 between Sullivan Square
Station and Central Square
Cambridge−Outbound
Route 94 between Medford Square
and Davis Square Station−Inbound
Route 94 between Medford Square
and Davis Square Station−Outbound
Route 96 between Medford Square
and Harvard Station−Inbound
Route 96 between Medford Square
and Harvard Station−Outbound
Existing
Midday
Service
Headways
Proposed
Midday
Service
Headways
Existing
Night time
Service
Headways
Proposed
Night time
Service
Headways
33.0
27.3
51.0
42.9
33.0
27.3
40.0
33.3
26.0
21.4
30.0
25.0
28.0
23.1
33.0
27.3
26.0
21.4
60.0
50.0
26.0
21.4
51.0
42.9
45.0
37.5
45.0
31.5
45.0
37.5
40.0
33.3
45.0
37.5
36.0
30.0
45.0
37.5
33.0
27.3
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MBTA THE RIDE Fleet Replacement
The MBTA’s paratransit service, THE RIDE, currently utilizes Ford Crown
Victoria model cars for part of its fleet, and almost exclusively for its fleet that
serves the GLX study area (Somerville, Medford, and Cambridge). THE RIDE is
proposed to replace 142 of the Ford Crown Victoria vehicles with 142 Ford
Fusion Hybrid vehicles, which would be assigned to operate in the study area.
The Ford Fusion vehicles use less gasoline, hence resulting in an air-quality
benefit.
Additional Commuter Rail Parking Spaces
The MBTA is building additional parking spaces for both the Salem and the
Beverly commuter rail parking garages. The Salem garage will add 374 spaces
and the Beverly garage will add 378 parking. Increased parking capacity would
induce a mode shift from auto to commuter rail transit, which in turn would result
in improved air quality.
2.
RESULTS
Table 3 below presents the estimated emissions reductions associated with the
above-described interim offset measures. These three strategies identified by the
MBTA—transit service headway improvements, THE RIDE fleet replacement,
and more parking at Beverly and Salem—would collectively exceed the budget,
that is the emission reductions anticipated from construction of the GLX project.
Note that the stationary-source emissions produced by additional Green Line
service were not considered in this analysis.
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TABLE 3
Emission Targets and Emissions from Interim Offset Measures Using
MOBILE 6.2 Year-2015 Factors
Emissions Reductions Goal and
Strategies
Target Emission Reduction Goal
(Emissions Reductions from Auto
Diversions from Building GLX) the
budget2
Emission Reduction from Added
Garage Capacity at Beverly and
Salem3,4
Emission Reduction from MBTA THE
RIDE Replacements3,5
Emission Reductions from 20% more
Vehicles per Hour for All Green Line
and Five Selected Bus Routes2,6,
Less New Emissions from Bus
Routes
Emission Reductions Subtotal
CO
NO X
VOC
VMT1
459.2
22.4
13.5
46,529
286.0
12.2
8.3
30,732
125.2
5.3
3.6
0
167.2
578.4kg
8.2
25.7kg
4.8
16.8kg
16,899
47,631kg
1VMT reductions include highway diversions from transit improvements and added garage spaces.
2Emissions estimates derived from CTPS travel forecasting model. 3Emission estimates derived from
spreadsheet. 4Added parking capacity at Salem (374 additional spaces) and Beverly (378 additional
spaces) with an assumed utilization rate of 80%. 5 Ford Crown Victoria vehicles assumed to consume 17
miles per gallon (mpg), Hybrid Ford Fusions assumed to consume 47 mpg. 6Off-peak headway
improvement for all MBTA Green Line branches (B,C,D,E) as well as MBTA bus routes 80, 88, 91, 94,
and 96.
CO = carbon monoxide. GLX = Green Line Extension. Kg = kilograms. MOBILE 6.2 = US Environmental
Protection Agency (EPA). Vehicle-emissions modeling software. NOX = nitrogen oxides. VOC = Volatile
organic compounds. VMT = vehicle-miles traveled.
2.1
Methodology
CTPS used a combination of methodologies to estimate the air-quality savings
that would result from implementing the above-listed suite of interim offset
measures. The primary estimating tool was the CTPS regional travel demand
model, in conjunction with the US Environmental Protection Agency vehicleemissions modeling software MOBILE 6.2; and CTPS used spreadsheet-based
models to estimate emissions benefits from fleet replacement and constructing
new parking spaces.
CTPS Travel Demand Model and MOBILE 6.2
CTPS used its travel demand model in conjunction with MOBILE 6.2 to estimate
the air-quality impacts associated with mode shifts from auto to transit based on
improvements in Green Line and bus service.
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The CTPS model is a four-step trip-based demand model that represents the
highway and transit networks in eastern Massachusetts. The model is comprised
of 2,727 transportation analysis zones (TAZs) and is capable of estimating mode
and route choices. Each of the four steps of the model describes a particular
aspect of trip making in eastern Massachusetts. The model generates trips
based on land use and demographic data, and distributes those trips according
to the relative attractiveness of the TAZs within the model. The model assigns
each trip to a particular mode based on the utility of that mode in terms of cost,
time, and distance. Finally, the model assigns each trip to a mode-specific
network, choosing between various route options based on congestion and travel
time information.
The routing information derived from the highway assignment portion of the
CTPS model is processed by MOBILE 6.2 to estimate mobile emissions from
vehicles. Pairing the routing information of CTPS’s regional model with MOBILE
software to produce mobile vehicle emissions is a methodology that CTPS has
used many times to analyze the mobile emissions of SIP projects. This approach
was used for the initial testing of the SIP project package in 2006, the
subsequent testing of the SIP project revisions accepted by the EPA (and
detailed in the Federal Register of July 31,2008), and for testing new SIP project
packages in 2009, 2010, and 2011.
Spreadsheet-Based Emissions Estimates
Staff used spreadsheet models to estimate the emission benefits as a result of
fleet replacement for the MBTA THE RIDE service, and construction of new
parking spaces at Beverly and Salem garages. Staff chose this methodology
because 1) the CTPS travel demand model does not represent non-fixed-route
paratransit service such as THE RIDE, and 2) staff had used spreadsheet
models in the past to analyze mobile-emissions impacts of new park-and-ride
lots.
CTPS obtained from the MBTA the average annual VMT data for THE RIDE
vehicles, which was used to calculate daily fuel usage for both existing THE
RIDE vehicles as well as the proposed fleet replacement vehicles. 1 CTPS then
estimated the daily fuel usage for an average MOBILE 6.2 fleet vehicle. 2 A
grams-per-gallon emission factor was then calculated for the MOBILE 6.2 fleet
vehicle. This grams-per-gallon factor was then applied to the fuel-usage
estimates for the existing and proposed THE RIDE fleet vehicles to estimate the
1
The daily fuel-usage calculation assumed a 17 mpg fuel efficiency for the Ford Crown Victoria and 47
mpg fuel efficiency for the Ford Fusion Hybrid.
2
The average fuel efficiency of a MOBILE 6.2 fleet vehicle is 24.1 mpg.
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savings that would result from replacing Ford Crown Victoria vehicles with Ford
Fusion Hybrid vehicles.
To estimate emissions improvements from the additional parking spaces at the
Salem and Beverly garages, staff used trip distance and speed data 3 from the
regional travel demand model in conjunction with MOBILE 6.2 emissions rates,
and assumed a utilization factor of eighty percent for the new parking spaces.
Each newly utilized parking space was assumed to capture a single-occupancy
vehicle (SOV) trip that otherwise would have driven all the way into downtown
Boston from Beverly or Salem. The associated emissions for these previously
made SOV trips were summed together to compile emissions reductions for this
measure.
3.
CONCLUSION
The three-pronged package of interim offset strategies—1) increasing off-peak
Green Line and bus services, 2) replacing MBTA THE RIDE fleet vehicles, 3) and
adding parking spaces at the Beverly and Salem commuter rail parking
garages—would provide more emission reductions than would implementing
GLX service.
SAP/BD/BK/bd
3
CTPS assumed one-way trip lengths of 28.4 miles and 25.7 miles from Beverly to Boston and Salem to
Boston, respectively; and assumed average speeds of 23 miles per hour between these origins and
destinations.
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