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The aim of this study was to assess whether patients with neurodegenerative disease, namely Alzheimer's disease (AD) and Parkinson's disease (PD), differed from age-matched, neurologically normal comparison participants in their ability to detect impending collisions. Six AD patients and 8 PD patients, together comprising the neurodegenerative disease group, and 18 comparison participants completed a collision detection simulation task where they must judge whether approaching objects would collide with them or pass by them. The neurodegenerative disease group was less sensitive in detecting collisions than the comparison group, and sensitivity worsened with increasing number of objects in the display and increasing time to contact of those objects. Poor performance on tests of cognition and visual attention were associated with poor collision detection sensitivity. The results of this study indicate that neurodegenerative disease impairs the ability to accurately detect impending collisions and that these decrements are likely the combined result of visual and cognitive disturbances related to disease status.

The purpose of this paper is to further improve the understanding of the relationships between measures of accidents (density and rate) and average daily traffic (ADT) on interurban road sections. The road sections studied are selected on the basis of carefully defined criteria. Power functions are fitted and classified according to: (i) a time-sequence analysis for each roadway section; and (ii) a cross sectional analysis on a one year basis. Each analysis covers both the total and individual accident types: multivehicle, single-vehicle and pedestrian involvement accidents. When the parameters of the power functions are presented in a matrix-format a linear dependency is observed between the power and the logarithm of multiple constant. The general functional form is that the total accident density which was found to increase with the increase of ADT, is the combined result of a sharp increase in multi-vehicle accidents, moderate decrease in single-vehicle accidents and a negligible effect of pedestrian accidents. The possible application of the findings is discussed and operative examples are given.