## 5 Interpretation of the Results and Future Works  
The above studies described have shown that it is possible to increase roundabout capacity by changing traffic regulations. Also, trucks have a significant impact on urban traffic fluidity: their growing share in the total number of vehicles (simulated in one of the experiments) led to a significant reduction of the roundabout capacity. In order to maximise the number of vehicles crossing a roundabout, it should be possible for vehicles to enter and exit the roundabout simultaneously. The multi-lane area of a roundabout can be  
Figure 17: Distribution of the number of CA iterations depending on the percentage of trucks. used most effectively, which results in capacity maximisation. This was demonstrated by Scenario 4. Such traffic organisation may be easily implemented, e.g., by appropriate marking of solid and broken lines within roundabouts. The analysis of urban traffic performed in Poland reveals that more appropriate marking may lead to increasing safety of road traffic participants. An additional criterion to improve traffic safety seems to be driver training. The observations of roundabout traffic have revealed numerous behaviours of drivers that generated unnecessary traffic collisions. Development of Scenario 5 was inspired by actual events observed at roundabouts. Many a time, the vehicles driving in the inner lane (in the case of 2-lane roundabouts) or in the middle lane (in the case of 3-lane roundabouts), when trying to exit the roundabout would cut in on the vehicles moving in the outer lane. It was observed that e.g., less experienced or elderly drivers tended to keep to the outer lane. The traffic organisation described in Scenario 5 could reduce such behaviours, which in turn might lead to increased traffic capacity in cities having a high number of roundabouts. Another aspect, which should be noted in order to increase traffic capacity, is reduction of freight vehicles on roundabouts affected by heavy traffic. Of course it is impossible to totally eliminate freight traffic in cities. However, it is possible to limit the number of trucks in cities, e.g., by providing ring-roads. Also, a controversial idea seems to be a prohibition to drive trucks in peak hours. When the number of trucks is significant and there are limited other possibilities to increase the traffic capacity, this idea might be taken into account. It should be emphasised that not each roundabout has the same shape or the number of entrances and exits. Moreover, a computer simulation takes into account merely a fragment of the reality. Nevertheless, the results of the study are promising and this issue deserves further attention. The model does not consider drivers' behaviour, experience, fatigue nor ongoing concentration in navigating through roundabouts. The future plans for this task include an ongoing linkage between the model and metrics form the urban system, which will record quantitative data (although it would certainly be useful to develop a methodology for automatically retrieving qualitative data such as vehicle data). The model also does not specifically look at the specific characteristics of pedestrians walking by the roundabout, treating them only as a parameter that has some influence on the scenarios studied. However, incorporating pedestrians' behaviour into the launched study may point to further important aspects. The developed model does not account for cyclists, either. The aforementioned facts show an area that could contribute to the subsequent studies in this respect. Other aspects that may be of some importance, but were not investigated, are the distances between the individual feeder roads. The developed model could also be extended to include the possibility of turbo roundabout simulations. It would require small modifications of the principles contained in Scenario 5. It also might provide an answer to the question whether in the case of a given roundabout it is better to apply the classical traffic organisation, or a directional traffic organisation.