TRAFFIC CONTROL DESIGN ELEMENTS FOR ACCOMMODATING DRIVERS WITH DIMINISHED CAPACITY. VOLUME II: FINAL TECHNICAL REPORT

A comprehensive review of technical information documented age-related decrements in sensory/perceptual, cognitive, and psychomotor functions likely to affect the use of standard traffic control devices. Analysis of accident data from two States plus older driver focus group discussions identified key driving situations and traffic control elements with which this user group experiences the greatest difficulty. Empirical (laboratory) and analytical studies followed, in each of the functional areas noted above. Results indicated significant problems for older relative to young and middle-aged drivers in the visual detection and recognition of pavement striping/delineation and of the legibility of highway sign legends; in the cognitive response to contingent multielement (sign-plus-signal) left turn control displays, as well as selective attention for specified color/shape categories of highway signing, and decision making with varying guide sign message formats; and in the speed of overriding one just-initiated response with one or more other vehicle control movements. A laboratory evaluation of preliminary countermeasure options also was conducted. Project findings indicated specific facilitative effects for older drivers of redundant upstream posting of the sign element in left turn control displays at intersections, the use of a redundant discrete format for changeable message signs, the use of larger and perceptually-dissimilar signs to convey the most critical message in a multiple/complex overhead traffic sign display, a 30-to-300 percent increase in the brightness of pavement markings, and letter sizes on highway signing that are at least 30% larger than standard practice currently provides.