Proposal:Two-stage bicycle turn

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Two-stage bicycle turn
Proposal status: Draft (under way)
Proposed by: Jarek Piórkowski
Applies to: to be determined
Definition: designated areas where cyclists wait to safely make a far turn (in right-hand-traffic regions, a left turn)
Draft started: 2020-04-09

Proposal

Looking for comments on possible tags for roadway infrastructure that allows cyclists to make safer two-stage far turns. (That is, in right-hand-traffic regions, make a left turn; in left-hand-traffic regions, make a right turn.)

Other possible names:

  • hook turn (w:en:Hook turn on Wikipedia, car-centric): avoids the left/right problem, term seems pretty widespread
  • indirect left turn (e.g. [1]): still has the direction; "indirect turn"?
  • two-stage turn, two-stage turn queue boxes (NACTO, MTO (pg 32))
  • two-stage bicycle turn box (MUTCD)
  • left turn bike box (York Region): also uses "two-stage left turn" and "Copenhagen left"

Rationale

Turn boxes or turn bays are paint- or curb-delineated places for cyclists to wait to do a two-stage turn from the near edge of the roadway.

In regions that allow right turn on red traffic signal, they are usually coupled with no-right-turn-on-red restrictions.

In many regions, left turn boxes are common to the point of being basically the default at bigger intersections, and thus don't really need tagging. However, other areas where cycle infrastructure is only beginning to be developed might have a single digit amount of them. As they make turns a lot safer, we would like to map them so that routers can prefer them and maps can display them.

Note that this is not the same as a cycleway=asl (advanced stop line, "bike box"): an ASL is behind the stop line and behind the pedestrian crossing, and thus not easily usable for left turns - cyclists have to cross the stream of pedestrians to get into the box.

Examples

Tagging

Several ways have been discussed on the tagging mailing list. These are summarized and implemented with an example below. Comments on any or all are welcome!

relation

This would use a relation with type=restriction:bicycle by analogy with French use of restriction:bicycle=give_way, see FR:Bicycle#Panonceaux de Cédez-le-passage cycliste au feu.

The relation would have Role from, Role via, and Role to members same as Relation:restriction#Members.

Discussion:

In regions where the use of the bike bay is not mandatory (that is, cyclists can still make a left turn from left lane even where bike box is present), a two-stage turn box gives more possibilities rather than takes away possibilities, so it isn't really a restriction. An alternative would be to create our own relation type, like type=bicycle_two_stage_turn. However, restriction:bicycle=* TagInfo restriction:bicycle=* is used 1500 times in France for give_way (where it makes stop optional for right turns at lights) so we could adopt that precedent.

At intersections with two-stage turn boxes on all four corners and possibly no-right-turn-on-red restrictions, this method requires up to 8 relations (4 for bike boxes and 4 for no-right-on-red). This is a lot, and suggests perhaps a related tag that could be placed on the intersection node? However: 1) no-right-on-red is already encoded in this way (up to 4 relations per intersection) in some areas of OSM; 2) a node tag if possible if and only if all directions of the intersection have the same kind of turn box, because node tags cannot adequately represent geometry of ways intersecting at the node; 3) and in areas where two-stage turn boxes are not common, the all-four-corner turn box intersections will still be quite uncommon, so the added relations might not be that much of a problem.

Examples in OSM:

lanes tagging

Since it's basically a short, mode-restricted turn lane, why not tag it as such?

Adapting the example of Lanes#Crossing with a designated lane for bicycles, we can arrive at following example tagging: https://bin.piorkowski.ca/2020/osm_bicycle_lanes_on_way.png 

 access:lanes:forward=||no
 bicycle:lanes:forward=||designated
 cycleway:lanes:forward=none|none|lane
 cycleway=lane
 turn:lanes:forward=left|none|left

Trying to go further and indicate also the through-going (painted) bicycle lane (as done in the wiki example linked above) I arrive at: https://bin.piorkowski.ca/2020/osm_bicycle_lanes_on_way_with_cycle_lane.png 

 access:lanes:forward=||no|no
 bicycle:lanes:forward=||designated|designated
 cycleway:lanes:forward=none|none|lane|lane
 cycleway=lane (possibly redundant?)
 lanes:bicycle:forward=2
 turn:lanes:forward=left|none|none|left

cycleway:forward=two_stage_box on node on source way

This is an analogy to highway=stop or highway=traffic_signal at the stop line before the intersection node.

cycleway:forward=two_stage_box would be placed on a node a little before the intersection, for cyclists' direction of travel. Routers would then look for a cycleway=two_stage_box node shortly before a possible left turn.

It is bit problematic geometrically: unlike with a stop sign where we can place the node on where the OSM way crosses the stop line (or a very short extension thereof), here the node needs to be a couple of meters away from the actual box, and not really in a geometrically meaningful position. (As far as I can tell the tag cannot be on the intersection node itself as I can't see a way to reliably indicate which of the crossing ways has a turn box.)

See example at https://bin.piorkowski.ca/2020/osm_cycleway_tsb_on_node.png (note is only explanatory here)

cycleway=asl node on intersecting way

This would put a cycleway=asl (advanced stop line) node on the intersecting way - not the part that cyclists are turning onto. This places an ASL node close to physical location of the turn box. Routers would then have to look for cycleway:asl=two_stage_left_turn a little to the right of where they'd like to make a left turn.

See https://bin.piorkowski.ca/2019/possible_asl_node_tagging.png for an example.

Advantages:

  • no relations - they seem to be somewhat disliked in OSM;
  • representation as turn-right-then-U-turn is somewhat like how cyclists are used to turning left at hostile intersections

Disadvantages:

  • the portrayed distance to turn off to right is further than the actual distance;
  • misleading, since the box is on a way not actually involved in the turn;
  • routers might well find it easier to find left turns as they would normally and then prioritize those with a bicycle_two_stage_left_turn relation

cycleway=two_stage_left_turn

This was suggested on tagging mailing list https://lists.openstreetmap.org/pipermail/tagging/2020-January/050104.html, but I am not clear on what element it would be used. Please consider cases where only one or two directions of the intersection have a two-stage turn box.

Applies to

Intersections. Whether this is done with node, way, or relation depends on adopted tagging.

Rendering

Uncertain. A small green or blue arrow pointing left on the right side of the roadway at the intersection (reversed for left-hand-traffic regions), perhaps?

Features/Pages affected

Probably mostly pages listing bicycle features.

External discussions

Comments

Please comment on the discussion page.

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