Understanding through trip patterns is crucial when making decisions concerning a traffic diversion strategy, such as whether to build a highway to bypass a city. While conducting a vehicle license plate origin-destination survey may be the most accurate way to estimate through trip patterns, many small communities may be unable to bear this cost. Thus, a simple and affordable sketch planning tool to estimate through trip movements would be useful. Three through trip estimation methods that have been used or published are Modlin’s method, Anderson’s method, and subarea analysis. Subarea analysis, while an effective tool, requires personnel with knowledge of modeling software, as well as a license for that software. Hence, subarea analysis may be of limited use to small cities and DOT district offices. Anderson and Modlin methods on the other hand are simpler to implement. However, these methods require some data that are not routinely collected, use parameters that can be highly subjective, and rely on calculations that may distort the results. To address some of the shortcomings of the existing methods, a logit-based external trip estimation method was created that had strong statistical justification. Evaluation of the logit model using small cities in Indiana yielded results that are usually better than Modlin’s and Anderson’s methods. The logit model is readily implemented in a spreadsheet and requires only two input variables. When subarea analysis using modeling software is not feasible, the logit model has been shown to produce good estimates of through trips.

Report Number



through trips, external trips, origin-destination matrix estimation, SPR-3095

SPR Number


Project Number


File Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version