User:Ojlaw/left turn lane View history

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'''Left-turn lane(LTL)'''
== Should the left turn lane be mapped? ==
Left-turn lanes should only be mapped in very limited circumstances-
* When there is a raised curb or median between the left turn lane and the through lanes for a long distance before the intersection that the driver might overshoot while waiting for a delayed "turn" audible. Wisconsin DOT calls these slotted left-turn lanes [http://wisconsindot.gov/rdwy/fdm/fd-11-25.pdf] [http://wisconsindot.gov/rdwy/fdm/fd-11-25-att.pdf#fd11-25a5.3]. The  main reason to map these in Wisconsin is the DOT has built many slotted left-turn lanes.
-or-
* When the turn lane physically separates from the main road well in advance of the intersection
* When the area is "busy" enough that the driver may not get any advance warning that a turn is coming up--in which case a left-turn lane lets you notify the driver a little earlier
* When there are user complaints (Update Requests) that the audible was too late, or that the map should have shown a left-turn lane
The routing server does not play nice with LTLs and will often create unnecessary right-turn/ U-turn or U-turn/ right-turn to route a left through these intersections. Often a junction box is required to help with routing when LTLs are created.
When in doubt, leave it out. Each left-turn lane complicates the map and adds to your workload when the time comes to check connectivity, direction, name, etc.
== {{anchor|How to label the connector type}} Road type ==
[[Image:Left_turn_Lane_1.PNG|right|border]]Essentially these left-turn lanes are the same road as the through road, we are just adding a segment for better turn instruction timing, so they should be mapped using the same road type as the through road.
*Ex: Street to Minor Highway should be Street type.
*Ex: Minor Highway to Primary Street should be Minor Highway type.
*Ex: Primary Street to Primary Street should be Primary Street type.{{clear}}
== {{anchor|How to name the connector}} Road name ==
In most cases, checking None for the Street name will be sufficient.  Navigation instructions will simply use the name of the next segment to which the left-turn lane segment connects.
If there are specific signs at the intersection which are confusing or contrary to the destination road segment name, then a name can be applied to the left-turn lane.
== {{anchor|Turn restrictions necessary for proper connector routing}} Geometry and Turn restrictions ==
In general using geometry is sufficient for the desired turn instructions- keep left instruction entering the turn lane and turn left instruction at the turn. When geometry won't work use TIOs for these instructions.
=== Divided road ===
[[Image:Left_turn_lane2.PNG|right|border]]Add turn restrictions to the left turn lane segment to prevent U-turn(if applicable) and right turns.{{clear}}[[Image:Left_turn_lane3.PNG|left|border]]Add turn restrictions to the adjacent through lane segment left turn(to force use of the left turn lane).{{clear}}{{clear}}
=== Non-divided road ===
[[Image:Left_turn_lane4.PNG|right|border]]Add turn restrictions to the left turn lane segment to prevent right turns.{{clear}}
[[Image:Left_turn_lane5.PNG|left|border]]Add turn restrictions to the adjacent through lane segment left turn(to force use of the left turn lane) and prohibit U-turns.{{clear}}{{clear}}
== Speed Limit ==
Left-turn lanes should be mapped using the speed limit of the segment feeding into the left-turn lane(unless signed otherwise).

Latest revision as of 13:52, 10 September 2019

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