Hello Dan, thank you for your answer.
The picture shows a city with a route layer. I created a drive time zone (15 min break, yellow color) at any point (red color) around. The result is one shapefile with the drive time polygons of each point.
The goal of my work is to find a location, from which i minimize the drive time to each point. That's why I asked for the central point. If I'm right, you can calculate the central point of all polygons (one big area within all drive time zones of all points), but the result is a middle point based on the bee line. I want to creat the central point based on the route layer. I hope you understand my problem now.