model of turn penalties?

[emiltin]

i understand turn penalties are not that far away, and what's essentially missing is just a good model. copenhagen university is intersted in helping out and provide parameters based on their research and data, but we need a better understanding of what such a model should consist of.

to get things started -
i imagine that there are 3 types of turns: normal turns, sharp turns, and u-turns, and that a penalty value is needed for each type of turn. so maybe something like:

side    type          angle range  penalty
--------------------------------------------
left    turn          20..160      0.1
left    sharp turn    140..160     0.3
left    u-turn        160..180     0.6
right   turn          -20..-160    0.1
right   sharp turn    -140..-160   0.3
right   u-turn        -160..--180  0.6

an alternative could be generalize this into a single 'continuous' formula that takes the angle as input and returns a penalty.

thoughts?

[DennisOSRM]

Yes, this sounds about right, but I imagine that such a formula needs some calibration. Also, depending of the actual line string of nodes (that model a way and its turns) there may be the need for additional analysis. I.e. It is not always obvious what degree a turn has. A continuous function is even better.

[emiltin]

i guess you could look at either just the intersections, or also how winding the ways are between intersections.
would it be possible to setup a branch with the turn penalty code, so we can experiment with such a formula?

[DennisOSRM]

renamed turn restrictions to turn penalties

[emiltin]

keeping this open, as it's not yet handled in the dev branch.
a working implementation of turn penalties handled in the lua profile is in features/lua_turn_penalties.

[MaartenDeen]

A few thoughts on turn penalties:
(1) http://osrm.at/2We
This route takes the motorway offramp and continues to the onramp because it is marginally shorter in distance and therefore (because of the speed limits) marginally faster. There is no turn involved, only the crossing of a secondary road. IRL the secondary road has the right of way, but of course the router does not know this.
To solve it you would also have to enter a turn penalty for 0 degree angles when other ways cross or branch off (this situation could also occur when there is a T-junction).

(2) http://osrm.at/3jr
This route takes a longer way via 80 km/h roads in favour of the shorter route via 50 km/h ways (N556 Stationsstraat). Again, correct following the shortest time calculation.
There are two roundabouts on the N556. Roads connecting to a roundabout usually have a (close to) 90 degree angle and so the short route will get penalized too.
And when does a curved road get penalized? N556 has some curves in it. Do you penalize that when there is no "going left or right"? But the calculated route takes an almost 180 degree turn in a way where you do not go left or right.

[MaartenDeen]

Another thought when I saw http://osrm.at/3lQ and http://osrm.at/3lR (the last one is routed via exit 39b and primary road Quai Perrache and may disappear because I set some maxspeeds).

How about a penalty when there is a change from a higher class to a lower class motorway? The first case has maxspeeds set as they are posted on the roadside and even though the routed way is 525 meters and 34 seconds while the preferred routing via the roundabout is 888 meters and 49 seconds, it is not the preferred way (as "Schans" is only a very narrow road, have a look at Google's streetview).
In this case the penalty would have to be at least 16 seconds, not including penalties that get taken by the roundabout.
Or generally add a penalty for using lower class motorways. Because even though certain roads have a posted speedlimit, this limit gets more and more theoretical when using lower class roads.
Germany comes to mind as a good example: non-urban roads (Landstrasse) have an implied speedlimit of 100 km/h but can be anything from a broad 2-lane (primary) road which invites to even higher speeds, to a narrow tree-lined road less than 3 meters wide where it is dangerous to go faster than 60 km/h.
The latter roads are usually tagged as tertiary or unclassified in OSM.

[emiltin]

turn penalty processing could be improved by passing the ways that touch the turn point, and the node. that way you could do things like increase penalty when crossing a big road without signals, etc.

[DennisOSRM]

Right, I am thinking about some exploration of surrounding area, but this is rather expensive

[TheMarex]

We are exploring using a data driven approach as opposed to a model driven one via #2306

[TheMarex]

We are determined to make this work with a data driven approach. Closing this for now.