Many severe accidents occur in urban areas. As part of the research project UR:BAN this study investigated how different types of visual warnings can prevent collisions within these areas and trigger the adequate reaction in critical situations. For this, two different warning types were implemented in a head-up display. It was assumed that one of the warning types should trigger an immediate and firm brake reaction of the driver (stop sign warning) whereas the other type of warning should animate the driver to be cautious, for example by slightly pressing the brake pedal (caution sign warning). As collisions in urban areas are also very difficult for older drivers, differences of the effects of the two warning types between older and younger drivers on driver performance (numbers of collisions, brake reaction time, maximum braking value) were examined. For this, four urban scenarios were implemented in a static driving simulator varying the characteristics of the critical object (e.g., pedestrian, lead vehicle, obstacle). In total 72 drivers (36 participants aged 20-35 years, 36 participants aged 65+ years) were tested in a between-subjects design (Age, Type of Warning). The study revealed that the number of collisions was reduced when drivers were warned (especially for younger drivers) demonstrating the positive effect of these warning types in very critical scenarios. If the situation is not very critical, warnings did not reduce the numbers of collisions, since the total amount of collisions was very already very low. In critical scenarios older drivers prefer the stop sign warning (leading to a faster and stronger brake reaction) compared to younger participants. This group had the fastest and strongest brake reaction when receiving the caution sign warning. In less critical scenarios both warnings had a positive effect on the braking reaction times for both younger and older drivers. The strongest brake reaction here was reached (in both groups) when receiving the stop sign warning. This study demonstrates the importance of design thoroughness when wanting to achieve effective warnings.