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TRAFFIC FORECASTING IN A VISIONING WORKSHOP SETTING 125 lines, in which case there may be no need to run the tran- inating feedback to trip distribution, running fewer sit assignment component of the model. assignment iterations, foregoing transit assignment, and limiting roadway assignment to two periods (peak and off-peak) that were then processed in parallel. THE SLOCOG AND SACOG SACOG also faced difficulties trying to edit networks VISIONING WORKSHOPS in a hurry. Attempting to add each project link-by-link was not practicable within the time constraints and The SLOCOG and SACOG workshops' goals and mod- would almost certainly have led to coding errors. This eling approaches differed substantially. With SLOCOG task was simplified by preparing a master file containing there was a consensus on future roadway projects but the existing road and transit networks along with a large not on land uses; the visioning workshops therefore number of potential projects--far more than could be focused on the type and location of future real estate included in the MTP. A GIS interface was developed that developments. SLOCOG had a geographic information allowed the links for each proposed project to be modi- system (GIS) program--Planning for Community, fied simultaneously from a drop-down menu. For exam- Energy, Environmental, and Economic Sustainability ple, a proposed 6-lane expressway could be converted (PLACE3S)--that enabled it to make quick changes in into a 4-lane arterial or eliminated by checking the land uses, and had recently developed a TransCAD appropriate box on a menu. While the option to edit the model with a fairly short run time (17 min). attributes of individual links was available, it was rarely SACOG, on the other hand, had already achieved a used because the participants tended to think in terms of broad consensus on future land uses through its award- entire projects rather than individual links. winning Blueprint Project. Its new round of workshops In each case certain constraints were placed on partic- was intended to create a consensus on future road and ipants to force them to face uncomfortable realities. In transit projects for its 25-year Metropolitan Transporta- the SLOCOG workshops participants were required to tion Plan (MTP). SACOG had a regional model that accommodate the forecast number of new residents and operated in a mixture of MINUTP and TP+ scripts with jobs. The SACOG workshop participants were limited a typical run time of more than 8 h. Table 1 compares to the programmable portion of the MTP budget, with the two modeling situations. project costs based on actual estimates (if available) or SLOCOG had the easier modeling task because its on average unit costs. original TransCAD model required only a few changes Five separate software packages were used in the to fit within the run time constraints. The smallest down- SLOCOG workshops. The land use data were edited in town travel analysis zones were consolidated and only a PLACE3S, which produced an output file readable in single period (daily) was run. In fact, the run time was Excel. Excel macros were used to reformat the data into fast enough that a team of three modelers was able to a file usable by TransCAD, which produced graphical service 15 tables of participants, thus eliminating the outputs and tabular indicators. These were combined need to bring in less-skilled staff. Moreover, editing land into a Word file for printing and distribution to the par- uses (for SLOCOG) turned out to be easier than editing ticipants at the originating table and into a PowerPoint links (for SACOG) and less likely to cause error. presentation for discussion by all the tables. Most of the SACOG faced the daunting task of needing to reduce processing time was spent transferring data from one its model's run time by 97%. It had hoped to achieve this software package to another. This arrangement was through hardware and software improvements; however, cumbersome and fraught with risk of error, which was the software upgrade had only a minor impact on run only somewhat mitigated by extensive practice prior to time. Therefore, the model had to be simplified by elim- the workshops. TABLE 1 Comparison of Features of SLOCOG and SACOG Workshop Models Feature San Luis Obispo COG Sacramento Area COG Inputs changed Land uses Road and Transit Networks Global constraint on inputs # of new DUs and jobs Total of Project Budgets Modeling software TransCAD Cube/Voyager Processing time (original) 17 min 8 h 35 min Processing time (workshop) 4 min 15 min Modifications made to model Fewer TAZs Fewer periods No feedback to distribution Fewer iterations Fewer periods No transit assignment Some parallel processing Projects as single entities Link to land use software Through Excel Embedded/automatic