U-turn Policies—Help | ArcGIS Desktop

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Reverse turns on the global turn delay evaluator

The global turn delay evaluator can be set up on any of the network dataset's time-based cost attributes. Since it is part of the network dataset, any network analysis layer solved on an impedance attribute that has an associated global turn delay evaluator is affected by the evaluator's current settings.

The Global Turn Delay Evaluator dialog box

Learn how to open the Global Turn Delay Evaluator

You can use the global turn delay evaluator to generically penalize left, right, straight, and reverse turns at junctions. U-turns double back on the same edge as the approach. Reverse turns are similar to U-turns, but reverse turns are based on approach and depart angles and don't have to turn back on the same edge. The next graphics demonstrate this idea.

Two roads intersect at an acute angle. An arrow shows a sharp turn to the left.
Here is a sharp turn at a street intersection. According to the settings of the Global Turn Delay Evaluator dialog box in the screenshot above, turns qualify as reverse turns if the angle of departure from the intersection is 30 degrees or less (60 degrees divided by two).
The reverse-turn pie wedge shows the turn qualifies as a reverse turn.
The reverse-turn wedge from the global turn delay evaluator is superimposed on the roads to show that the turn is sharp enough to qualify as a reverse turn.
The reverse-turn pie wedge is superimposed on streets that meet at a wider angle
If a similar turn is made on this intersection, it would not qualify as a reverse turn. Although the turn is sharp, it falls outside the reverse-turn range, and would qualify as a left turn instead.

U-turns double back on the same road as the approach, so they always qualify as reverse turns.

Assigning a prohibitively high penalty to reverse turns has the effect of restricting U-turns. However, the global turn delay evaluator can only penalize time-based impedance attributes, so if your impedance is distance based, for example, the global turn delay evaluator is not an option for setting a U-turn policy.

One benefit of the global turn delay evaluator is that if the network has hierarchies defined, penalties for reverse turns can vary based on the hierarchies of the roads that converge at a junction. For instance, making a reverse turn on a local road at an intersection with another local road could be lightly penalized, essentially allowing U-turns in those situations.

Learn more about global turns

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