Austin/San Antonio Origin-Destination Study: Sensitivity Analysis of Traffic Diversion Methodology (1186-3F)

This report presents the results of sensitivity analyses performed on a traffic diversion methodology developed to estimate the potential demand for an alternate route in the Austin/San Antonio corridor. Two earlier research reports present the results of an origin-destination (O-D) survey conducted to identify travel patterns in the study corridor, and the results of the use of that survey data to estimate the traffic diversion potentials of a proposed alternate route, based on the assumption that the alternate route would be a four-lane, limited access facility (i.e., comparable to I-35). This report presents an extension of the analyses described in the two earlier project reports. Specifically, the analyses presented in this report examine the traffic diversion potentials of a four-lane divided highway without access controls. The analyses were directed at: 1) Evaluating the effects of varying the assumption concerning the amount of time savings necessary to induce traffic to divert to the alternate route; and 2) Evaluating the diversion effects of varying the assumed travel speed for the alternate route. The resulting estimates of diverted traffic were evaluated and a "best estimate" of the diversion potentials of a four-lane divided highway without access controls was identified. The results of the analyses indicate that the alternate route offers only modest time savings over other roadways in the corridor. Small reductions in assumed travel speeds, or small increases in the assumed time savings necessary to induce diversion produce dramatic reductions in the estimates of alternate route traffic.