User:Atrophicshiner/sandbox

Turn lanes

Firstly, the majority of junctions do not need turn lanes at all. Waze gives advanced warning of upcoming turns, it is up to the user to pick the relevant lane for the approaching turn. Turn lanes are only really needed if they are really long, or the junction is sufficiently complicated to need clearer navigation instructions.

When not to map turn lanes

• When the turn lane is too short (<200ft)
• When the turn lane is not distinct from the main carriageway
• When the turn lane splits at or near the main carriageway stop give way line.

Turn lane too short

Turn lane not distinct

Splits at or near stop line

When turn lane may need mapping

• When the turn lane splits from the main carriageway with a physical barrier separation
• When an acute angle may lead the user to misunderstand the location of the turn
• When mapping only some of several turn lanes at a junction unbalances that junction
• For better control of u-turns when junction is too wide to trigger the u-turn prevention mechanism
• Complex junctions that benefit from additional instructions.

File:Example.png Physical barrier separation

File:Example.png Acute angle of junction

File:Example.png Balanced junction

Complex junction

If turn lanes really are of benefit to the driver, then they should be mapped in the following way:

• The turn lane segments should have no name, so that the instructions read out the name of the next street.
• The Road Type should match the type of the roads they lead to (and never ramps). Only the main carriageway stays as the higher Road Type.
• The angle at the beginning of the turn lane should be shallow, so that Waze says Keep Left / Right at that point.
• The end of the turn lane should have a clear turn instruction near to the give-way point, unless the traffic merges onto the new road with right-of-way.