take into account expense of doing a u-turn when routing

[grenzdebil@…]

When the user intentionally leaves the route, navit will always give the instruction to make a 180-degree-turn and return to the route, even when it would be less time-consuming in real life to go on and take a slightly different route than the one originally computed by navit. (to turn around, you first have to find a suitable place to do it, stop, let opposite traffic pass, etc.)

For example: you drive down(up in the ascii example) a main road (A) and navit wants you to turn right at the junction of A and B to get to the target. But you decide - no matter why (maybe because of traffic jam on A) - to turn right at the junction of A and C, go down C, turn, follow D and turn right at the junction of D and B.

+----B-----+------>target
|          |
|          D
+----C-----+
|
A
|
^
start

When on C, navit will urge you to turn around and follow A again.

I am no expert in routing algorithms, but I think if there was some value added to the total "expense" of a route when it involves doing a u-turn on a "one-lane-two-directions-road", better results could be archieved in most of these cases.

Of course the direction of movement has to be known.

[KaZeR]

I personally also vote for this. Turning around is often impossible, and almost always dangerous.

[mvglasow]

How about a configuration setting "avoid U-turns"?

[https://wiki.navit-project.org/index.php/user:elhaard]

Today, I saw another reason to vote for this:

    ---+----B---+--------------------->target
       |        | (no right turn)
       D        A
       |        |
       +---C----+
                |
                |
                ^
              Start

Near me, there is a situation like above. There is a turn restriction (no right turn) from A to B.

If you are driving on A and go right on B, then the best thing to do is to turn left into C, right into D and then right into B.

But today, Navit (svn version 4418) insisted that I should just turn left on B and make a U-turn instead. As B is rather congested, making a U-turn is not easy at all.

This type of problems would also be fixed by adding to the cost of making a U-turn.