On a daily basis drivers have to share the roads with a great number of other road users. To make the driving task possible every driver has to take the intentions and behaviours of other road users into account. In other words, the road users have to interact with each other. The general aim of this thesis was to examine factors that regulate and influence the interaction between road users. To do so, three studies, applying a social psychological approach to driving, were conducted. In the first study it was investigated how the rules of priority, the design of the intersection, and the behaviour of other drivers influence yielding behaviour in intersections. The second study examined driver irritation and its relationship with aggressive behaviours. Finally, in the third study drivers’ attributions of their own and other drivers’ behaviour were investigated in relation to driver irritation. The thesis also includes a minor field study, aiming at examining to what extent informal traffic rules are used in intersections and in roundabouts, as well as measuring the validity of self-reports. The results indicate that, in addition to the formal rules, drivers rely on informal rules based on road design and on other drivers’ behaviour. Drivers also differ with respect to strategies of yielding behaviour. Irritability and aggressive behaviour on the roads appear largely to depend on drivers’ interactions and drivers’ interpretation of the behaviour of others. Some aggressive behaviour is an expression of irritation and may provoke irritation of other drivers. This means that an irritated driver might start a chain reaction, spreading irritation and aggressive behaviour from driver to driver. To diminish irritation and aggressive behaviour on the roads it is necessary to change drivers’ behaviour either by changing the road design or, which is probably a more possible remedy, by changing their general attitudes about driving. By providing drivers with insight into the cognitive biases they are subject to when judging other road users’ behaviour, both driver irritation and aggressive behaviours on the roads probably would decrease.