I think two of the reasons why regional travel models often wind up with traffic assignment procedures that may be over-simplified in their representation of link-to-link-to-link auto or commercial vehicle travel times between two zone centroids are:ġ) The lack of meaningful model validation/testing procedures (which includes "validation over time" checks).Ģ) The uncertainties as to "so what to do next" if the testing reveals some big differences between predicted and observed. To: TMIP Subject: Re: Intersection Delay in Travel Demand ModelĬonsider these as nothing more than personal observations, which are presented in the hopes this may stimulate some clear thinking on the topic. Path choice involves link/turn-level decision making.įrom: Kenneth.Cervenka= on behalf of KenCervenka Sent: Wednesday, J10:12 AM We cannot necessarily assume that good OD travel times lead to good path choice estimates. ![]() Ideally, if an agency wanted to use regional-model outputs for project-level work, that regional model should have a dynamic traffic assignment or another equally good way of calculating delay at controlled intersections and at other locations where substantial queueing can occur. ![]() Those better delay estimations methods may be incorporated into regional models, hybrid models or subarea models, as appropriate. Regarding your "Regarding #2" comment, second paragraph, NCHRP Report 765 reiterates multiple times that good delay estimates are essential to project-level forecasts.
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