Proposal:Two way lane

Two-way lane
Proposal status:	Abandoned (inactive)
Proposed by:	imagic
Tagging:	two_way_lane=tidal_flow / median / passing
Applies to:
Definition:	A two-way lane is a lane in which traffic may travel in either direction, depending on certain conditions.
Statistics:
Draft started:	2012-03-26
RFC start:	2012-03-26

In many countries lanes exist on which traffic may travel in either direction. This proposal introduces a new key, which can be used together with the lanes extension to tag those lanes.

Rationale

From Wikipedia:

A reversible lane (British English: tidal flow) is a lane in which traffic may travel in either direction, depending on certain conditions. Typically, it is meant to improve traffic flow during rush hours, by having overhead traffic lights and lighted street signs notify drivers which lanes are open or closed to driving or turning.

A passing lane has referred to a lane in the center of a highway meant for passing in both directions. Neither direction has the right-of-way, and both directions are permitted to use the lane for passing. In a similar layout, three lanes are striped with two in one direction and one in the other, but traffic in the direction with one lane is allowed to cross the centerline to pass. 2+1 roads have replaced some of these in Europe and North America.

Another type of center two-way lane is a center left-turn lane (for countries which drive on the right), center turn lane or median turn lane, a single lane in the center of the road into which traffic from both directions pulls to make a left turn.

Tagging

 two_way_lane=[tidal_flow|passing|median]

Value	Description
tidal_flow	A tidal flow (reversible) lane is a lane in which traffic may travel in either direction, depending on certain conditions.
passing	A lane in the center of a highway meant for passing in both directions.
median	A single lane in the center of the road into which traffic from both directions pulls to make a right/left turn.
no	Not a two-way lane of any kind.

If this key is used on the whole OSM-way, it would mean, that there exists one tidal flow/passing/median lane on that way. So if you only want to tag the existence of a center turn lane you simply write two_way_lane=median.

This key becomes much more useful if combined with the lanes extension and this would also be the recommend way. See the following examples for this.

Examples

Three lanes and a tidal flow in the middle

 highway=primary
 two_way_lane:lanes=no|tidal_flow|no

Four lanes and a median turn lane

 highway=primary
 two_way_lane:lanes=no|median|no|no

Further improvements (not included)

This proposal only suggest the introduction of the two_way_lane key. If we want to fully describe tidal flow lanes we need more information. In this section I show how this could be done and also explain why I didn't included it in this proposal.

Condition for travel direction

Even if we can tag a tidal flow lane, we are still missing

• the conditions on which the travel direction depends, and
• the travel direction itself.

I would suggest tagging the travel direction using the direction=* key (please note: the values forward and backward are not yet defined for this key):

 two_way_lane:lanes=no|tidal_flow|no
 direction:lanes=forward|backward|backward

But the direction of the middle lane changes during the day. If we want to tag these also, we need conditional tags. There already exists a proposal for conditional access keys. I would strongly recommend to create a common solution for conditional tags and not invent individual ones for any existing key. Therefore I don't want to address this here further. Just for the sake of completeness I add here an example how it could look like:

 two_way_lane:lanes=no|tidal_flow|no
 direction:lanes=forward|backward|backward
 direction:lanes:conditional=forward|forward|backward [time(10:00-20:00)]

The direction:lanes specifies a default traffic direction for the middle lane and the direction:lanes:conditional overrules this for some given daytime.

Simple tag for the number of lanes

In the :lanes proposal it was already suggested to introduce the suffix :both_ways by analogy with :backward/:forward. Using this the number of lanes running in both directions could be tagged just like the number of lanes running forward/backward:

 lanes:forward=1
 lanes:backward=1
 lanes:both_ways=2

Comparison with centre_turn_lane

There exists a proposal to only tag center turn lanes. There it is suggested to tag those with centre_turn_lane=yes.

According to wikipedia: Most often done on three-lane roads, the reversible lane is typically used for traffic in one direction at morning rush hour, the opposite direction in the afternoon or evening, and as a turning lane at most other times.

If we want to tag this situation (with some further improvements as explained above) with separate keys like tidal_flow=yes and centre_turn_lane=yes we could use:

 centre_turn_lane:lanes=no|yes|no
 direction:lanes=forward|both_ways|backward
 centre_turn_lane:lanes:conditional=no|no|no [time(05:00-10:00; 15:00-20:00)]
 tidal_flow:lanes:conditional=no|yes|no [time(05:00-10:00; 15:00-20:00)]
 direction:lanes:conditional=forward|forward|backward [time(10:00-15:00)]
 direction:lanes:conditional=forward|backward|backward [time(15:00-20:00)]

Whereas if we use one single key for all kinds of two-way lanes:

 two_way_lane:lanes=no|median|no
 direction:lanes=forward|both_ways|backward
 two_way_lane:lanes:conditional=no|tidal_flow|no [time(05:00-10:00; 15:00-20:00)]
 direction:lanes:conditional=forward|forward|backward [time(10:00-15:00)]
 direction:lanes:conditional=forward|backward|backward [time(15:00-20:00)]

Still an awful number of awfully long tags, but at least one tag less.

Comments

Please use the Discussion page for this.

See also

• Proposed feature centre_turn_lane: centre_turn_lane=[yes|no]
• Proposed feature Reversible lanes: lanes:reversible=* and lanes:reversible:type=*
• direction=*
• Lane dependent tagging
• Proposal for conditional access keys