|Allowed/forbidden lane changes|
|Definition:||Define which lane changes are legally allowed and which one are forbidden|
This proposal introduces the key change which allows to specify the allowed/forbidden lane changes. This key is only useful if used together with at least one of the suffixes :lanes, :forward or :backward or on oneways.
Especially navigational devices need the information what lane changes are allowed resp. forbidden to give the driver accurate instructions, e.g. on complex motorway interchanges.
The value of the key specifies what kind of lane changes are allowed or forbidden. The following values are possible:
|yes||It is legally allowed to change the lane in any direction physically possible. This does not mean that is is physically possible to leave the lane in both directions. On the leftmost lane of a road the value yes is equivalent to not_left, on the rightmost lane it is equivalent to not_right.|
|no||It is legally forbidden to leave the lane.|
|not_right||It is legally forbidden to change to the lane on the right side, but allowed to change to the lane on the left side.|
|not_left||It is legally forbidden to change to the lane on the left side, but allowed to change to the lane on the right side.|
|only_right||It is legally forbidden to change to the lane on the left side, but allowed to change to the lane on the right side. Equivalent to not_left.|
|only_left||It is legally forbidden to change to the lane on the right side, but allowed to change to the lane on the left side. Equivalent to not_right.|
The direction of the lane change is usually viewed in the direction of the OSM way. If the key is used together with the suffix :backward (i.e. either as change:backward=* or change:lanes:backward=*) the direction is viewed in the opposite direction of the OSM way.
|A one-way road with three lanes. It is legally forbidden to enter or leave the rightmost lane. This is a common case at the beginning of acceleration lanes on motorways. The value not_left|not_right|no would also be possible and would have the same meaning.|
|A four-lane road with two lanes in the same direction as the OSM way. When driving on the left lane it is allowed to leave the lane in both directions, i.e. either to the lane on the right, or to the lane on the left which is a lane of the oncoming traffic.|
|A four-lane road with two lanes in the opposite direction of the OSM way. When driving on the left lane it is not allowed to change left onto a lane of the oncoming traffic.|
|A road with two lanes, one for each driving direction (the tag oneway=no is not necessary in this example). Any lane changes are forbidden. |
Note: This is not equivalent to overtaking=no! For example, if overtaking is forbidden it would also be forbidden to overtake a motorcycle with a car. If only lane changing is forbidden and the lane is wide enough it would be legally allowed to overtake the motorcycle.
Be cautious when tagging two-way roads. The values not_left and not_right are viewed in the direction of the OSM-way unless they are used in conjunction with the :backward suffix. Therefore it is strongly recommend to always use the :forward/:backward suffix on two-way roads. One exception from this rule might be the tag change:lanes=*no|no (see the example above).
Different values on a three-lane motorway
The following example assumes that the OSM way runs from left to right.
Part 1: change:lanes=yes|yes|yes Part 2: change:lanes=no|not_left|yes Part 3: change:lanes=yes|not_right|no Part 4: change:lanes=no|yes|no Part 5: change:lanes=yes|no|yes
Why not left and right as value?
Because those values are not intuitive. Does left mean you are allowed to change to the left lane or you are allowed to change only to the left lane?
What about junctions?
The key change=* only specifies lane changes. It does not tell you anything about turning restrictions.
Example: on a road where no lane changes are allowed, you do not need to split the way at junctions and allow within the junction lane changes. So in a situation as depicted right, the following tags are correct:
- Part A: lanes=2 + change:forward=no + change:backward=no + turn:forward=left;through
- Part B: lanes=2 + change:forward=no + change:backward=no
- Part C: lanes=2
If turning left would be forbidden, you have to use the the relation restriction.
The style Lane and Road Attributes visualizes also the change-tags directly while editing.
Please use the Discussion page for this.