1. A method for determining real-time delay information in a transportation system, the method comprising: receiving, by a processing device, historical operational information about the transportation system, wherein the historical operational information comprises data related to a plurality of arrival events corresponding to one or more stops within the transportation system; building, by the processing device, a dependency graph based upon the historic information, wherein the dependency graph defines a plurality of relationships that exist in the transportation system between the plurality of arrival events, and wherein each of the plurality of relationships defines a specific dependent relationship between at least two of the plurality of arrival events; fitting, by the processing device, a plurality of delay dependency values into the dependency graph, wherein each of the plurality of delay dependency values is associated with one of the plurality of relationships and defines a specific dependency value associated with that relationship; determining, by a processing device, predictive delay information as determined based upon the fitted dependency graph for one or more of the plurality of arrival events based upon current operating information related to the transportation system; outputting, by a processing device, an indication of the predictive delay information; receiving at least one real-time observed delay for the at least one of the plurality of arrival events associated with the parent node; propagating the delay through the fitted dependency graph; and returning real-time predictive delay information based upon the propagation.