A combination of factors including an unattractive public transport offering a low level of service, the lack of parking facilities, an inadequate drivers’ education and poor policing have led to illegal parking phenomena in many Greek cities, contributing in their aesthetic and cultural degradation, making them inaccessible for both vehicles and pedestrians. In the present study the phenomenon of illegal parking is investigated along selected road axes in the city of Thessaloniki, Greece. After the appropriate processing of the data collected, the impact of illegal parking on the reduction of road capacity was calculated. Moreover, it was attempted to relate illegal parking activity with the type of adjacent land uses. Conclusions regarding the degree of parking violations and the road capacity reduction in relation to road and adjacent land uses’ characteristics are given and possible measures and policies towards the alleviation of the problem are proposed.