As the Boston Region MPO develops JOURNEY TO 2030, it will use its regional travel model to forecast future travel conditions. The model is a computer simulation of the transportation system and its use. To represent different possible future conditions in the region, planners vary the inputs into the model, which include demographic projections and alternative sets of transportation improvements. Thus the MPO can forecast the effects of alternative investment decisions. The findings from a series of model runs will help guide the selection of projects for JOURNEY TO 2030.

The MPO has performed the first model run, in which it used as the inputs a transportation network based on the current long-range transportation plan (adopted in 2004) and “baseline” demographic projections to the year 2030 that are derived from past trends. These demographic projections were compiled by the Metropolitan Area Planning Council (MAPC), the regional planning agency for the Boston area. The inputs are detailed below, along with the resulting outputs of the model.

INPUTS FOR THE FIRST MODEL RUN

Demographics
MAPC recently completed baseline demographic projections in which past trends were used to project conditions in the year 2030. These projections were the demographic inputs in the first run of the regional travel model.

Compared to 2000, the baseline projections show the population of the model area growing by 10.8 percent (from 4.3 million to 4.8 million residents) and the number of employees growing by 10.3 percent (from 2.3 million to 2.6 million).

The projected growth is not uniform through the area: one quarter of the region’s population growth is projected to occur in just 20 communities, and half of the region’s new jobs are projected to be in four major job centers comprising 27 communities. In terms of percentage gain in population, the fastest-growing communities are along I-495, where land is available for development. The population of these communities is projected to grow 20 percent or more over the next 30 years.

An important demographic trend apparent in the projections is the aging of the population. As baby boomers age, the proportion of residents over the age of 55 in the region will grow from one in five to one in three. This trend is the major reason for the growth in single-person households (up 48.9 percent) and zero-worker households (up 54.4 percent) indicated by the baseline projections.

Transportation Network
For the first model run, the MPO used the 2030 transportation network set forth in the current long-range transportation plan, with the addition of two projects: the Green Line to West Medford and Union Square, and 1,000 new park-and-ride spaces in the region.
Air Quality Assumptions

The MPO uses outputs of MOBILE6 software to determine the emission rates for various air pollutants. These rates are then applied to the trips forecast by the model, to determine total emissions for the region. MOBILE6 inputs take into account many projected improvements that will reduce stationary and mobile-source emissions, including:

• Emission limitations for new vehicles
• Vehicle fleet turnover
• Low-emission-vehicle programs
• Vehicle inspection and maintenance programs
• Vapor recovery systems at gas pumps
• Fuel vapor pressure improvements

OUTPUTS OF THE FIRST MODEL RUN

With the inputs indicated above, the model projects that total daily trips in the region will rise to 19.3 million by the year 2030 from 16.8 million in the year 2000, an increase of 15 percent. Of these trips, those with their origin or destination outside the region are shown to grow 65 percent, to 3.4 million trips, by the year 2030, when they will represent 18 percent of all trips.

Despite the fact that the mode share of automobiles decreases by 1.4 percentage points, average weekday vehicle miles traveled increase 17.7 percent, from 108.3 million to 127.4 million, and average weekday vehicle hours of travel rise 23.4 percent, from 3.4 million to 4.1 million. Average roadway speed decreases 4.8 percent, from 32 miles per hour to 30.7 miles per hour.
Overall transit boardings increase 11.4 percent, with the most growth occurring in commuter rail and express bus ridership.

Air Quality Results
Mobile-source emissions are reduced, despite a forecast increase in vehicle miles traveled, mostly due to the implementation of the programs listed above.

• Carbon monoxide emissions decrease 58 percent
• Volatile organic compound precursor emissions decrease 78 percent
• Nitrogen oxide emissions decrease 91 percent

FUTURE STEPS

Selection of Preferred Demographic Inputs
MAPC, in consultation with the MPO, will develop a second set of demographic projections, based on values emerging from the MetroFuture planning initative. The MPO staff will run the regional travel model using these projections and the same transportation network inputs used for the first model run, to produce a second set of outputs. These outputs will be compared with those of the first model run. The MPO will then select a preferred demographic projection for use in developing the JOURNEY TO 2030 transportation plan.
No-Build Scenario

Once the MPO selects a preferred demographic projection, a 2030 scenario will be modeled using as inputs that projection and the transportation network that exists today. This scenario will be called the no-build scenario, because it does not contain any future transportation improvements. It will be used as a baseline in comparing the effects of alternative sets of transportation improvements in build scenarios.

Build Scenarios
Using the regional travel model, the MPO will compare alternative future transportation networks in order to evaluate the relative benefits of different transportation investments. The projects to be assessed will be selected from a universe of projects developed during the MPO’s public outreach for JOURNEY TO 2030. Each project will be evaluated in terms of the MPO’s policies in these areas:

• System preservation, modernization, and efficiency
• Mobility
• Environment
• Safety and security
• Regional equity
• Land use and economic development

JOURNEY TO 2030 Transportation Plan
The final, fiscally constrained group of projects chosen for the transportation plan will be modeled to demonstrate its effect on air quality and on the provision of transportation serving low-income and minority populations.