To accommodate the establishment of a new nursing home in Deizisau, a community underground garage with a single lane entry and exit is to be expanded with additional public parking spaces. The study demonstrates the impact of the underground car park on the surrounding road network. The traffic volumes, daily traffic distribution curves and the origin/ destination of the forecast traffic for two utilization alternatives were determined. In light of the forecast increase in the traffic volume, the impact on the adjacent residential streets was investigated. Furthermore, considering the expected daily variation in traffic distribution, the single lane entry and exit situation was evaluated and possible solutions to the parking garage entrance situation were presented.