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{{@|Where speed limits change}}
[[Speed limits/USA|Click to view the USA Speed Limits Wiki Page]]
== {{@|Where speed limits change}} ==
Speed limits should change where they legally go in effect for your state, that may be at the sign, a specified distance before the sign, or the nearest intersection. When a speed limit changes in the middle of a segment, {{u|a new junction should be added to support the SL change}}.
* However '''a new junction should never be added for a SL if it will be within 200 feet of an existing junction''', or potential junction.
* A new junction should always be added if it will be more than 1,000 feet from the nearest existing, or potential junction.
=== {{@|Creating a new junction for a speed limit change}} ===
When creating a new junction solely for the sake of showing a speed limit change, you can attempt to get more value from the junction. Survey the area around the speed limit change, determine if there is a PLR or other segment which should be connected to the road and would result in a junction. You may find that there's a parking lot which could benefit from being added to the map within the allowable distance of 200 feet (or more depending on your area) to where the SL changes. In such a case connect that segment and use that junction. Otherwise you should create a new junction to show where the SL changes.
On roads where traffic for one turn direction typically backs up waiting to make the turn further than 200 feet, and traffic going straight or turning the other direction does not have to wait as long to pass through, turn delays can be affected even with the new junction 200 feet away. In these cases you may choose to extend the buffer zone to beyond the point where traffic backs up, and instead make the change at an existing junction node. These situations are governed by editor discretion and local guidance.
It is very important that we do not create new junctions too close to existing intersections, yet marking the speed limit change too far can have a negative impact on the user experience.
The minimum distance of 200 feet was chosen because a distance less than that is negligible, and unnoticeable in the client experience. It is not much different than the delay we expect with GPS lag and error anyway. For example think of where you hear the turn prompts announced, they can sometimes precede a junction by up to 200 feet.
We have confirmed directly with the routing developers that adding a junction node connecting only 2 segments does not have an associated [[routing penalty]]. We have also confirmed that creating and adding new junction nodes where necessary using these above guidelines will not have a negative effect on route calculation.
However there is a legitimate concern when adding new junctions too close to existing intersections / interchanges, that they may interfere with and pollute the ability for Waze calculate accurate [[turn delays]].
The reason to use a minimum of 200 feet from the nearest junction as a buffer is to account for turn delay calculations.
If we create junction nodes very close to intersections we will effectively eliminate Waze's ability to differentiate the time it takes to go straight, vs the time to turn left or right. {{u|A distance of less than 200 feet between junctions poses a significant risk to the ETA calculations (turn delays).}} Over 200 feet it is up to local practice , and the editor's discretion to determine if a junction node there will negatively impact turn delay calculations. We must stipulate a minimum buffer zone, but it doesn't need to be exact. The area between 200-1,000 feet is open to interpretation, editor discretion, and local guidance.
If an exit or turn lane does back up over 1,000 feet, it is unlikely that traffic beyond the 1,000 mark will be drastically affected by the new junction placed that far away. ''However specific exceptions with the consultation of Regional Coordinators, or State Managers will always be allowed.''
: The turn delay issue could potentially be mitigated by adding [[User:CBenson/Junction_Box|Junction Boxes]] to each of these situations to correct them. However doing so would result in a lot more work for editors, and a lot more strain on the servers. It would make it harder to manage these intersections since all the included segments, and turns get locked from editing. It will have an effect on route calculation timing as well. We therefore had to come up with a compromise that is still visibly accurate, without anything being noticeably different to the client user, yet maintaining the ability for Waze to calculate proper ETA timing through intersections.
| the rationale behind these rules.}}
== Military Bases ==