U-turns not prevented at split edges

[hbruch]

Is your feature request related to a problem? Please describe.
As a driver, I usually don't want to perform a U-turn. OTP's SimpleIntersectionTraversalCalculator currently provides costs for safe and accrossTraffic turns, but not for U-turns.

EDIT: U-turns are currently usually prevented by an isReverse check in StreetEdge.doTraverse() and state dominance checks. However, this fails under some very special conditions, e.g. when an edge is split by a linked transit stop and the dominance check allows visiting a vertex multiple times because the vertex is close to the request origin/destination. Splitting currently introduces two distinct split nodes so the isReverse check does not recognize the split forward/backward edges as reversed (see comment below).

Goal / high level use-case
Preventing U-turns.

Describe the solution you'd like
I suggest to add costs for U-turns (e.g. between 170 and 190 degrees) in SimpleIntersectionTraversalCalculator.
I suggest to use the same split vertex for forward and backward edge.

Describe alternatives you've considered

• Add an additional, custom IntersectionTraversalCalculator as Sandbox Feature, which would need an extension of IntersectionTraversalCalculator.create to be included.
• EDIT: extend isReverse check to handle special case of split vertices with same coords but different IDs. This has the downside that this check will happen in a performance critical section of the routing algorithm.
• EDIT: add costs for U-turns (e.g. between 170 and 190 degrees) in SimpleIntersectionTraversalCalculator. Turning across traffic already has an additional cost while doing a U turn has not.

Additional context
The city of Aachen, Germany wants to inform their citizen about upcoming super block turn restrictions. For this use case, a custom OSM extract was generated, which contains these restrictions. Evaluating these restrictions, OTP's routing circumvents some of them suggesting U-turns:

[hbruch]

As discussed in todays developer meeting, the above routing behavior looks like a bug that should already be addressed in

OpenTripPlanner/src/main/java/org/opentripplanner/street/model/edge/StreetEdge.java

Lines 1069 to 1078 in 20fc8ce

	if (backEdge != null) {
	// No illegal U-turns.
	// NOTE(flamholz): we check both directions because both edges get a chance to decide
	// if they are the reverse of the other. Also, because it doesn't matter which direction
	// we are searching in - these traversals are always disallowed (they are U-turns in one direction
	// or the other).
	// TODO profiling indicates that this is a hot spot.
	if (this.isReverseOf(backEdge) || backEdge.isReverseOf(this)) {
	return null;
	}

However, this apparently seems not to work in case of split edges, where forwardEdge and backwardEdge are split by different splitNodes: