Despite the prevalence of electronic navigation systems, road signs remain important. For one thing, positioning is sometimes not precise enough in complex intersections. For another, they help verify virtual directions (navigation system) against real-world conditions (signs). Currently, the German signposting guidelines (RWB – Richtlinien für wegweisende Beschilderung) stipulate the so-called 4/10 rule, which means that one sign can display a maximum of 10 destinations in total and a maximum of 4 per direction on the kind of yellow signs posted along most roads other than freeways. This rule is based on theoretical and practical considerations.
Example of the 4/10 Rule
Increases in traffic and road network density raise a number of questions.
- How much time do drivers have to read signs?
- How much information should be displayed on a sign so that it can be read and processed safely without negatively affecting traffic?
- Can the number of destinations displayed on a sign be increased by using pictograms?
To answer these questions, a field trial was conducted which involved eye tracking while signs were read on freeways, highways and urban roads.
The average time available to read signs on freeways is:
- 5.4 seconds for overhead signs,
- 4.2 seconds for signs on the side of the road.
The average time available to read signs on country roads and urban roads is 3.0 seconds.
