Distraction due to variable speed limits

This paper presents a field study in Finland, to investigate how the presence of even simple variable message signs (VMS), with important information such as speed limits, may divert drivers' attention from adjacent fixed signalling. The effects of speed limit signs, using fibre-optic technology, on recall of a nearby fixed warning sign were examined, and the effects of a fixed speed limit sign were used as a control. The hypothesis tested was that a speed limit sign using fibre-optic technology is more disturbing than a fixed speed limit sign. The experimental site was located on an inter-urban road with fixed 8Okph speed limit. The test signs were: (1) a variable speed limit sign, using fibre-optic technology; (2) a fixed speed limit sign; and (3) a fixed general warning sign with an additional plate carrying the message "TRAFFIC INVESTIGATION". Speed data were collected by two pairs of detector loops, one before the signs and one after them. 950 drivers of various ages were interviewed, of whom 71% were male. Results were obtained on recall of the signs and on driving speeds. It was found that drivers were less likely to recall the warning sign when it was near the fibre-optic sign than when it was near the fixed speed limit sign. The results are compared with those of some other relevant studies.