To improve their capability to estimate the emissions reduction benefits of the new bicycle facilities, the Association of Monterey Bay Area Governments (AMBAG) and the Monterey Bay Unified Air Pollution Control District sought to develop a new software tool. The tool was required not only to deliver accurate forecasts with a small development budget, but also operate independently of other models, run on a platform that can be freely distributed without special software licenses, and provide user-friendly access to planners in multiple agencies with varying levels of technical skill.

To satisfy these requirements we developed an incremental nested logit mode choice model that pivots off of static exports of trip tables from AMBAG's existing four-step travel model. Global positioning systems traces collected from smartphone users in the region were analyzed to estimate a path size logit route choice model, and the California Household Travel Survey was used to estimate a scaling coefficient on the best route utility. The model is implemented in an Adobe ActionScript graphical user interface (GUI). After the user edits the bicycle network in the GUI, new bicycle levels-of-service are skimmed, and new shares for each mode are calculated from their original shares in the no-build alternative and the change in the bicycle level-of-service. Finally, the emissions reduction is estimated based on the distance and average speed of the vehicle trips substituted by bicycle travel. The result is an accurate, fast, freely-distributable, user-friendly tool that is consistent with the forecasts produced by the four-step model.