TRAVEL DEMAND AND THE 3DS - DENSITY, DIVERSITY, AND DESIGN

The built environment is thought to influence travel demand along thre e principal dimensions-density, diversity, and design. This paper test s this proposition by examining how the '3Ds' affect trip rates and mo de choice of residents in the San Francisco Bay Area. Using 1990 trave l diary data and land-use records obtained from the U.S. census, regio nal inventories, and field surveys, models are estimated that relate f eatures of the built environment to variations in vehicle miles travel ed per household and mode choice, mainly for non-work trips. Factor an alysis is used to linearly combine variables into the density and desi gn dimensions of the built environment. The research finds that densit y, land-use diversity, and pedestrian-oriented designs generally reduc e trip rates and encourage non-auto travel in statistically significan t ways, though their influences appear to be fairly marginal. Elastici ties between variables and factors that capture the 3Ds and various me asures of travel demand are generally in the 0.06 to 0.18 range, expre ssed in absolute terms. Compact development was found to exert the str ongest influence on personal business trips. Within-neighborhood retai l shops, on the other hand, were most strongly associated with mode ch oice for work trips. And while a factor capturing 'walking quality' wa s only moderately related to mode choice for non-work trips, those liv ing in neighborhoods with grid-iron street designs and restricted comm ercial parking were nonetheless found to average significantly less ve hicle miles of travel and rely less on single-occupant vehicles for no n-work trips. Overall, this research shows that the elasticities betwe en each dimension of the built environment and travel demand are modes t to moderate, though certainly not inconsequential. Thus it supports the contention of new urbanists and others that creating more compact, diverse, and pedestrian-orientated neighborhoods, in combination, can meaningfully influence how Americans travel. (C) 1997 Elsevier Scienc e Ltd.