Traffic counts versus DEIR projections

This graph shows recorded traffic volumes (ADT = average daily trips) on Genesee Avenue and on Nobel Drive during the past 15 years. Despite a period of intense growth and development in North University City, traffic on Genesee Avenue has in fact remained roughly constant -- with a slight decrease -- since 1989. Will the DEIR projections for Genesee Avenue ever be realized, or is it yet another example of overprojected traffic?

The DEIR forecasts 42,000 ADT on Genesee, assuming no project, at 2030 build-out. This is consistent with -- and even somewhat smaller than -- the predictions in 1994 (49,000 ADT) and 1997 (45,000 ADT).

To what extent should we trust the traffic forecasts? Though it is undeniable that the 1987 forecasts were egregiously high, it is generally assumed that as land use models have increased in complexity and detail, and as computing power has improved enormously, traffic forecasting is perhaps accurate at the 20% level. This is significant, because if the prediction of 42,000 ADT is 20% too high, the corrected value of 34,000 ADT corresponds to level-of-service D, which doesn't justify any project. Given Genesee's intrinsic capacity beyond that of generic four-lane major streets, it may be that relatively minor improvements, such as intersection widening at Governor Drive, would suffice, even if the forecast is accurate.

The graphs below show measured traffic counts as a function of time for four segments along Genesee Avenue and Nobel Drive. The dotted lines in each graph show the predicted 2030 build-out volumes along these segments, assuming no project is built. Traffic is a highly nonlinear phenomenon, and the results of forecasts of volume on local arterials depend sensitively on assumptions about the freeways (e.g. whether or not HOV lanes are added). Naive extrapolations of traffic counts are not expected to yield particularly accurate results. Nevertheless, the historical data do suggest that Nobel Drive may "fill up" faster than Genesee Avenue.