Use of the Mobility Gap to Quantify Rural Transit Needs

The Colorado Department of Transportation undertook a statewide transit needs assessment. A critical component of the project was to define public transportation need in a way that could be quantified and easily calculated from available data. This was particularly important in the rural areas and smaller cities around the state which have not developed good estimates of public transportation demand. The authors developed a methodology based on a concept called the Mobility Gap. The Mobility Gap was defined as the difference in household trip rates between those households with automobiles and those households without automobiles. Data from the 1995 National Personal Transportation Survey were used to determine trip rates for households stratified by age and vehicle ownership. Trip rates were weighted based on household size to account for differences in average size of households with and without vehicles. The Mobility Gap was then calculated using these adjusted trip rates. The Mobility Gap is then applied using census data and the number of households without vehicles within each county to determine the number of trips which could potentially be served by public transportation. The difference between the potential trips calculated using the Mobility Gap and the actual transit trips provided within the county indicates the unmet need for public transportation. Use of the Mobility Gap was a new approach for defining rural public transportation needs. The approach is easily applied and relies on data readily available to any planning agency. The methodology was successfully applied for the entire state of Colorado.