A method, apparatus, computer program product, and device with various means are disclosed for determining the time it takes to a traverse a transportation structure by enclosing a representation of a transportation structure with a bounding polygon, specifying a plurality of gates which represent legitimate entry or exit points of the transportation structure as one or more edges of the bounding polygon, and computing the travel time for a probe traveling through the bounding polygon via the gates. Computing the probe's travel time comprises generating a location trace of movement of the probe, determining an entry and exit time, and calculating the difference between the exit time and the entry time. Determining the entry and exist time can be done by interpolation. An average of a set of computations can be used to get an average of the time it takes traverse the transportation structure.