Turn Penalty Effects on Minimum Time Paths

The transportation planning process is dependent upon the minimum path algorithm to develop the more logical route from the origin zone to the destination zone using the existing or proposed street system. Current philosophy assumes that an intersection turn penalty is necessary in order to prevent the algorithm from selecting illogical, stair-step paths through a grid street network. Minimum path trees for three levels of network detail were constructed with a turn penalty of 0.20 min and without a turn penalty. The differences resulting in the minimum path trees were examined to determine which path was the more logical. From these comparisons, it is concluded that the use of a turn penalty tends to produce a greater number of less logical routes, and the general practic of using turn penalties should be discontinued when level-of-service speeds are used in coding the representation of the street network.