Citation

Morris RS, Mounce JM, Button JW, Walton NE. Transp. Res. Rec. 1977; 628: 19-25.

Copyright

(Copyright © 1977, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

This paper reports an investigation of the effect of rain on the visual performance of drivers. The degradation of static visual acuity in terms of visual angle, detection probability, and legibility as a function of rain intensity was determined by experiments that used a rainfall simulator that produced artificial rain. The significant findings include the following: (a) Water on the windshield is the primary factor accounting for reduced visual performance, (b) visual degradation in the daytime with windshield wipers in operation appears to be a linear function of the rain rate with normal drop sizes, (c) during nighttime conditions, drop size is a significant factor in reducing visual performance (smaller drops are a more serious problem than is the rain rate), (d) wiper speeds above 50 CPM do not improve visual performance, (e) without windshield wipers, visual performace is reduced to levels that are unacceptable for driving (equivalent to visual acuity greater than 20/200) at rain rates greater than 2.5 cm/h (1 in/h), and (f) the effective rain rate can be determined from the vehicle velocity, the terminal velocity of the drop, the rake angle of the windshield, and the actual rain rate.