Mobility indicators can serve many purposes. They should provide trend information from which implications for transportation can be drawn or from which transportation policy and investment decisions are made. They can provide a basis for comparisons among metropolitan areas. They can provide the public with a sense of whether system performance is improving or getting worse. And in conjunction with intelligent transportation system strategies, they could be used on a real-time basis to inform travelers of current “mobility conditions” of the transportation system so that travel decisions can be made with full knowledge of what to expect. This subgroup concluded that for purposes of the BTS initiative, mobility indicators are best used for trend analysis and comparisons.
It seems likely that with the right selection of indicators, the public and the media would be quite interested in this information. The Texas Transportation Institute congestion index receives yearly national attention when the latest data are released. A “travel temperature” index developed at Georgia Tech, which uses travel time contours to give up-to-date information on expected travel times, received international attention because the traveling public easily understood it. Information such as this is likely to be well received by transportation system users.
There was a strong sentiment for having at least a single mobility index that could be used by local officials to assess how their metropolitan area is doing over time. We could easily provide a set of measures that provide indications on a variety of system characteristics, as well as one overall mobility index.
It was also noted that an unreliable system places greater emphasis on safety, security, and, of course, reliability. Such system performance characteristics definitely need to be part of a performance measures set, although not necessarily in a mobility index.
The above definition of mobility leads to the identification of several performance characteristics that should be included in any set of mobility indicators that reflects what is of interest to the traveling public. These characteristics include: