Case Study:

San Francisco Bay Area, California

Methodology

Calculation of Threshold-Based Accessibility

The data requirements for this computation include:

• Employment and population in each zone in the analysis area; and
  
• Zone-to-zone travel times for each mode of travel under each of the alternatives to be compared. These travel times can be obtained from output of the regional travel demand model.

MTC uses MinUTP software as the basis for its regional travel demand model. MTC staff have developed a inNUTP-compatible Fortran program known as "ACCTMTX" that tallies the zones within a specified travel time "contour" and then tallies the employment within these zones. The output of this program is then analyzed using standard spreadsheet software (Excel); statistical software (SAS); and mapping software (MapInfo). The MTC's accessibility analysis was based on a.m. peak-period travel times computed separately for the highway, transit, and HOV 3+ networks. More information about the MTC's travel model is available through the MTC's DataMart.

The resulting measure, A_ik, is the sum of all jobs accessible within an X-minute travel time of zone i by mode k. This is computed for each zone. To compute overall regional accessibility, A_k, for mode k, the employment accessible from each zone is weighted by the population of the zone, as follows:

As an example, the average Bay Area resident can reach 71,722 jobs within 30 minutes travel time by taking transit during the a.m. peak period.