Transportation Planning Process

Don’t be confused when you discover that your town or state does things its own way—they all do.

Federal transportation law lays out some guidelines and standards, but for the most part, the process differs from state to state and continues to evolve with every new highway bill.

Each town and state has established its own schedule, its own set of actors, and its own standards and processes. The planning process is continuous and comprehensive, so there’s always planning going on somewhere, and often, there’s no clear beginning point or finish line.

Several steps can take place at once and planners may repeat some steps several times. The basic steps in the transportation planning process are:

• Define the problem, scope, area, issues
• Set goals, objectives and criteria
• Collect data
• Develop alternatives and scenarios
• Model—forecast future travel behavior
• Evaluate alternatives
• Select a preferred plan
• Implement the plan through projects

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Travel Modeling

Transportation planners rely on complex mathematical models of the “real world” that can be used to show the impact of changes within the transportation system—such as adding a new road or transit line, or increases in population or employment. Current planning regulations require that MPOs have an analytical process in place for evaluating projects, but state transportation plans do not have the same requirement.

While all planning departments may use their own variation, most use some form of the basic four-step approach in modeling transportation demand.

1. Trip generation: Estimate the number of trips generated in each zone, destined for locations in other zones. Trip estimates are based on assumed relationships among socioeconomic factors, land use patterns and the existing number of trips.
2. Trip distribution: Develop a trip table showing the number of trips originated in each zone and destinations in each zone.
3. Mode split: For the number of predicted trips between each origin zone and destination zone, estimate the number of trips made via each mode available for that trip. Modes include driving alone, carpooling, using transit, etc.
4. Network assignment: Estimate the number of trips per mode for each possible path throughout the road and transit network. Assign all trips to a network. Compare the capacity of each road or transit segment to the projected demand to forecast the level of congestion to be expected at that location.

Four-step models are used to predict transportation demand, but planners and engineers also use other models to predict performance and resulting impacts.

Impact models determine the likely effects that new roads will have on the surrounding environment and community, such as air quality, noise and community impact.

Cost models estimate the likely costs of transportation projects, calculating, for example, dollars per linear foot of rail line. Some of the newer cost models incorporate “life-cycle” costing to estimate expected costs, both capital and operating, for a possible project over the expected life of that project.

What’s wrong with models?

Models can never provide a definitive picture of the future; they are only intended to provide estimates or “guesstimates.” Traffic forecasts can be affected by demographic changes and trends in economic growth and development, which can never be predicted with certainty. Moreover, transportation planners have been using the same models for the past 40 years.

In theory, by projecting the future performance of roads, transportation planners can accurately determine how and where to expand the network. In fact, much of the methodology we use for transportation planning was developed to build highways in urbanized areas such as Chicago, Detroit and New York in the 1950s. But we’ve changed more than hairstyles since the 1950s.

Issues such as air quality, sprawl, energy crises and global warming were not on the radar screen back then. Therefore, models based on that time period may be inappropriate today.

Both ISTEA and the Clean Air Act Amendments of 1990 brought about improvements to modeling by requiring consideration of land use, air quality and multi-modal options. However, all models are limited by the very assumptions, factors and alternatives that are explicitly included in the equations used by those models.  Even today’s models can be insensitive to non-automobile modes of travel, resulting in overestimating the demand for new highways and underestimating the effectiveness of alternative, less car focused scenarios. If we keep asking the same questions of the models, we will continue getting the same answers. And more of the same adds up to less habitat for wildlife.

Planning Studies

In addition to models, transportation planners rely on planning studies to develop concepts early in the planning process. A planning study is a defined set of activities performed to identify transportation problems and solutions. Studies can be conducted at the statewide, regional, sub-area, corridor or route levels.

Some studies are the direct result of a state or regional plan that highlights a particular problem. Each planning study results in a concept that will require further scoping and design to develop into a construction project ready for delivery. Planning studies vary significantly in content and coverage.

Corridor studies focus on an existing facility such as a highway or a broad geographic area that connects major destinations, such as two cities. The corridor width extends well beyond the facility right of way and may extend miles on either side. Responding to a specific problem (such as a high accident rate, congestion or land-use changes), corridor studies identify deficiencies and evaluate alternative solutions using a long-range outlook of 20 or more years. The finished study usually includes a description of the proposed facility and potential environmental impacts.

Other study types include:

• corridor management plans
• transportation systems analyses
• route development plans
• alternate route analyses
• spot/locations studies
• environmental review documents - these are sometimes considered planning studies

Planning and Air Quality

When do transportation planners consider impacts to the environment? Until recently, the only environmental consideration required during transportation planning was air quality.

Our car loving culture is a great contributor to air pollution, pumping four of the six most reviled pollutants into the air—ozone, carbon monoxide, particulate matter and nitrogen dioxide.

Locations that fail to meet air quality standards as defined by the Clean Air Act are called non-attainment areas and are tasked with developing a State Implementation Plan (SIP). SIPs contain emission budgets and establish measures to reduce emissions from stationary, area and mobile sources in order to attain or maintain air quality standards.

Transportation plans must demonstrate that projected motor vehicle emissions from planned transportation projects will not exceed the budget established in the SIP.

If the air quality in a particular location does not meet goals set out in the air quality plan (SIP), the state transportation agency will not receive federal transportation funding, except for essential safety projects and those projects with prior commitments. In fact, these sanctions may be imposed even if the lapse of conformity is not transportation related.