Case Study:

Montgomery County, Maryland

Conclusions

Strengths

Montgomery County's use of accessibility measures provided a number of benefits for comparing transportation alternatives. The measures indicated clear differences among the alternatives and also provided insights into the relative benefits to automobile and transit users. Furthermore, the measures proved useful in comparing longer-term combinations of land use patterns and transportation networks. The measures are clear, easy to understand, and can be computed based on available land use and travel demand model data.

The accessibility measures also point out an interesting finding that conventional measures of transportation system performance hide: accessibility may increase in the future, even though traffic congestion and travel times may also increase. Furthermore, the measures indicate that the gains in accessibility can be realized exclusively by changes in land use patterns, given the same transportation network. Projected growth in employment means that residents will have access to a greater absolute number of jobs than they currently do. Based on this particular accessibility measure at least, the growth in employment outweighs the increased travel "impedance" caused by increased traffic congestion.

Another question important to the use of accessibility measures is how to value these measures when making comparisons among alternatives. Montgomery County approached this by developing a "cost-effectiveness" index to identify the alternatives with the greatest accessibility benefits per unit cost. This approach is similar to calculating a cost-effectiveness index for emission reductions or other benefits that cannot easily be valued in monetary terms.

[TOP]