Trip Internalization in Multi-Use Developments

Internal trip capture refers to how the number of trips to and from a development are reduced by the proximity of complementary land uses within the development (e.g., residential to retail). Internal trips occur within the development and do not encumber the traffic flow on the public roadways connecting the development with the transportation network. Internal trip capture rates are used to estimate trip generation on mixed-use developments by adjusting the single land use estimates. These single land use estimates tend to overestimate the trip generation behavior for mixed-use developments. Accurate internal trip capture rate estimates and methodologies are necessary to improve the trip generation estimates for mixed-use developments. Nationwide, there have been efforts to enhance both the data availability and estimation methodologies to estimate internal trip capture rates. In this project, internal trip capture data from four mixed-use developments in Florida were collected and analyzed using a recently-enhanced internal trip capture methodology developed by the National Cooperative Highway Research Program (NCHRP). Results showed that the enhanced methodology produced generally more accurate estimates than those from the traditional Institute of Transportation Engineers (ITE) internal trip capture procedure. In the NCHRP methodology, the maximum unconstrained internal trip capture rates from land use pairs are chosen in mixed-use developments. Data collected in this project can potentially contribute with 33 percent of these unconstrained internal trip capture rates used in the enhanced methodology for internal trip capture estimation. A series of prediction tests was developed to assess the contribution of the unconstrained internal trip capture rates supplied by this study to the accuracy of the trip generation estimates. It was found that the use of the revised unconstrained internal trip capture rates based on the combined NCHRP and Florida Department of Transportation (FDOT) data improved the prediction capability in five out of eight test cases, with one test case tied. In addition to internal trip capture estimates, this project also collected transportation mode and internal trip length information. Guidance for improving the data collection process and estimation are also provided.