SACOG currently maintains two regional travel demand forecasting models: the Sacramento Regional Travel Demand Model (SACMET), and the Sacramento Regional Activity-Based Simulation Model (SACSIM).
SACMET is a traditional "four-step" travel demand model, originally developed by SACOG in 1994, with major updates 1996, 1999, and 2001. SACMET was used for travel forecasts for the MTPs adopted in 1996, 1999 and 2002. A post-process to more fully capture land use and transportation effects of density, diversity (mix of use), design, and destination (the 4Ds) was developed by SACOG in 2002, as part of the Blueprint project. SACMET plus 4Ds post-processing has been used for regional travel forecasts for the MTP workshops, evaluation and screening of preliminary project alternatives, and for evaluation of the final MTP.
SACSIM is a newly developed activity-based tour model. While SACMET represents land use data in a system of 1503 traffic analysis zones (TAZs) with median size of 300 acres, SACSIM represents land uses at parcel level. SACSIM represents travel activities as "tours" or series of trips connecting activities a person engages in during the course of a normal day. These aspects of SACSIM are cutting-edge features for a regional travel model and have the potential for capturing more aspects of land use and transportation interactions, as well as the effects of demographic changes-like aging of the population-on travel.
Both SACMET and SACSIM are fully operational travel demand models, with validation results well within published guidelines for regional travel demand models. Both models are being maintained and used to allow for comparison of results, and to allow more time to refine and fully understand and utilize SACSIM as a tool for transportation planning. Over time, SACOG expects to move from SACMET to SACSIM as the primary platform for regional travel forecasts. At this point in its development, it is believed that SACSIM may be slightly less sensitive to some 4D's land use factors than is SACMET plus 4Ds, which results in the more conservative SACSIM forecasts. SACMET results are provided in addition to SACSIM where noted on tables and figures.