Isochrones are an often-used, traditional instrument in traffic and town planning. For instance, isochrones might be used to analyze the optimal position of a planned public transport stop or to analyze reachability. Unfortunately, in the real world, application isochrones are rarely calculated well. Instead of using actual isochrones, planning offices evaluate the distance rn the average person walks in n minutes, shorten rn by a detour heuristic and create a circle with radius rn and center point m to approximate the n-minute isochrone. But even proper isochrones are fundamentally flawed. They either assume the walking speed for every person to be identical or guess the walking speed more pessimistic. Obviously, both methods are massively misestimating the area within an isochrone and can lead to misinformed decisions. Using one universal walking speed underestimates the area in the isochrone for some people, overestimates the area for others. Pessimistic walking times underestimate the reachable area for most people. The central flaw of the approach is the use of the expectancy value of the walking speed. The distribution of pedestrian walking speed has already been determined statistically. Thinking in distributions immediately allows more precise statements about reachability, margin of error and would benefit the understanding of modal choice. This paper aims to introduce the concept of isostochochrones, which build on top the concept of isochrones. Allowing the use of walking speed distributions and independent delay distributions at multiple points in a network allows clear margin of error statements and leads to deeper understanding of the planning situation.:Ziel der Arbeit Isostochochronen Isostochochronen ersetzen Isochronen Isostochochronen sind eine Erweiterung der Isochronen Zufallsvariablen und Mittelwerte Heuristiken müssen abgeschafft werden Relevante Planungsziele identifizieren