A comprehensibility study was conducted of traffic filter lanes at roundabouts with physically separated lanes. The question to be answered was what combination of road markings and road signs would lead to the best comprehensibility. In order to answer this question, images were generated by a computer, and subjects moved through an environment while approaching such a roundabout. Based on the results of an expert meeting, four factors were included in the study: (1) road signs, using the variants: (a) advance directions signs (ADSs) only, (b) ADSs combined with roadside signs, (c) ADSs combined with overhead signs, and (d) ADSs combined with overhead signs with down pointing arrows; (2) type of arrow road marking, using the variants: (i) without any arrow, (ii) a short roundabout arrow, (iii) a long roundabout arrow, and (iv) a standard arrow; (3) type of roundabout (4-direction and 5-direction roundabout); and (4) learnability (does comprehensibility increase after more than one encounter). At the beginning of the simulated rides, every subject received a given destination. Then the ride started and everyone had to answer two questions. First of all, one had to indicate as quickly as possible whether the left or the right lane would lead to the destination. After this, one had to answer what exit on the roundabout itself one had to take. The study showed that in the situation with the ADSs only, arrow road markings are required in order to make the right decision for a specific lane and for the right exit at the roundabout. The long roundabout arrow seems to be the most suitable. If it is preferred not to use any arrow road markings, ADSs combined with roadside signs and ADSs combined with overhead signs are the best. The combination of ADSs and overhead signs with down pointing arrows is not to be recommended.
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