The function of the road sign system as an information channel for car drivers was investigated. The data were gathered from more than 5,000 car drivers stopped after passing a road sign on a Swedish highway. The main results are as follows.

1. The overall probability of a road sign being noticed on passing is not higher than about 0·5.

2. The different signs studied form a scale of recording probability of perception extending from a low group with a probability of being perceived of about 0·25 up to a group with probabilities between 0·60-0·75. The rank order of the signs is consistent between occasions.

3. The results verified the outcome of a previous investigation by Johansson and Rumar, 1966.

The main conclusion must be that the road sign system to a high degree does not achieve its purpose.