TRANSPORTATION RESEARCH BOARD
TCRP Project H-41 addresses the need for new measures of the environmental benefits of transit investments. The objective of this research is to present, evaluate, and demonstrate criteria, metrics, and methods for assessing and comparing the environmental performance of major transit investments. For purposes of this research, the following definitions are used:
• Criteria: the characteristics that will be considered when performance is judged.
• Metric: a measure for something; generally a quantitative measurement or estimate, or an ordinal metric in the case of qualitative evaluation.
• Method: a way of doing something, especially a systematic technique or process used to develop a metric.
The research was undertaken in two phases. The first phase included
• a review of the literature to identify performance measures used for transit and other transportation projects, including a review of international practice in transportation environmental evaluation;
• interviews with 20 stakeholder agencies or groups;
• a review of four recent transit project alternatives analysis (AA) documents or environmental impact statements (EIS) to identify which environmental performance measures have been emphasized and how they have been treated;
• an enumeration of potential metrics of environmental performance, data sources and calculation methods, and preliminary screening of these metrics; and
• development of a more detailed approach to screening and selecting metrics, including selection of a short list of less than 20 metrics to evaluate in detail.
In the second phase, six pilot projects were recruited on which to test these metrics. Data were collected for each project and metrics were computed. Next, the ease of data collection and computation, reliability, and usefulness of each metric for purposes of distinguishing among transit projects were evaluated. Metrics were then placed in three tiers according to how promising they were for use in both local and national-level project evaluation. Finally, a set of “most promising” metrics was selected from the Tier 1 and Tier 2 metrics that represented each category of environmental performance without overlapping.
Table 1 summarizes the metrics that were considered most promising for use in comparison of projects or project alternatives. Any of these metrics could be used in the evaluation of different project alternatives. The table also identifies additional development activities that are needed before the metric is ready for use, particularly for comparing multiple projects in different regions. These metrics represent broad environmental performance issues of interest for comparing across projects (including benefits), rather than a detailed enumeration of all the environmental impacts considered in the environmental documentation process. The list includes only metrics that can be computed with existing data sources and modest resource requirements, and therefore is limited in its ability to fully represent some aspects of environmental performance.
Although these metrics were tested on only a few real-world projects, an initial review suggests that projects that perform well on some measures may perform poorly on others. This suggests that it is worth looking at a variety of metrics, because they illustrate different effects that may not be closely correlated. It also suggests that the choice of weights for each metric will affect how a project rates on overall environmental performance compared to other projects.
About the Transportation Research Board
“The mission of the Transportation Research Board (TRB) is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, TRB facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provide expert advice on transportation policy and programs; and disseminates research results broadly and encouraged their implementation.”