The Visibility of Vehicle Number Plates

Abstract

Despite the legibility of a vehicle registration plate being both a legal requirement for the vehicle owner and a test for the eyesight of a potential driver, no published experimental work on the visibility of number plates has appeared in this country. Moreover, a seven-character registration plate with smaller characters has recently been authorised by the Ministry of Transport. This paper describes two sets of experiments which form the first stage of a general experimental study on the day-time and night-time visibility of the new registration plates. The first series of tests was designed to discover the most common mistakes made in reading number plates. The results are shown in a table of ‘character confusion’ and indicate, inter alia, that differences in the central portion of two characters are less likely to be recognised than are peripheral differences. The second series of tests was designed to compare the frequency of mistakes in reading a number plate in good daylight with the visual acuity of the observer. This showed that virtually no mistakes are made by an observer of acuity 6/7.5 or better in reading a clean plate at 25 yards. The effect of reversing the contrast of a number plate is to make inaccurate seeing even less accurate.