When traffic moves between two roads that are at the same grade, these connecting segments are not technically ramps to Waze (with some [[[At-Grade_Connectors#Exceptions|Exceptions]]). When and how to implement an at-grade connector (AGC) in Waze depends on circumstances.
This article suggests additional clarity to the Waze wiki regarding At-grade connectors, focusing on when they are and are not called for. It is a personal work for local purposes and is not offered nor reviewed as a contribution to the US or Global wiki.
Applications
The rule for AGCs is "when in doubt, leave it out." For most intersections, separately mapped turn lanes confer no benefit. They add to the complexity of the display and substantially increase the effort required to verify connectivity, turn restrictions, directionality, name, etc. AGCs can also confuse routing for drivers who request a route while waiting at a stoplight on or near the AGC. If Waze snaps the driver to the AGC, it will offer a route assuming the driver is committed to the turn, which may not be the case.
Editors sometimes add AGCs because the satellite image suggests a separate turn lane when viewed with high magnification. This is never a good enough reason to map an AGC.
The following applications support use of an AGC.
Represent a physically separate road corridor
Ideally, AGCs represent physically separate, distinct road corridors that connect two larger roads at the same elevation. The physical corridor must be sufficiently isolated from the roads it connects that typical drivers would expect to see it explicitly depicted on the map, much like a freeway ramp. Update Requests from users that the map should show a connector warrant this application.
Prevent incorrect driver locating
Where frontage roads parallel very wide and intersecting highways for an extended distance, AGCs at the intersections may discourage Waze from snapping drivers to the frontage roads. This is uncommon.
Properly route side-road access
Sometimes side roads, especially parking-lot roads, connect near intersections in such a way that the side road can only be accessed from a separated right-turn lane. Drivers being routed to the side road must first diverge from the main road, while drivers emerging from the side road can only turn right and then continue along the right-turn path. Such a side road requires joining to an AGC to ensure proper routing.
Prevent "missing road" errors
Tracks that appear to Waze to be "cutting the corner" may cause Waze's automated missing-road detection algorithms to flag a Map Problem. In tests in early 2014, a "corner cutting" path straying as far as 30 m from a junction was not enough to throw this error, but a path straying 65 m was. The actual threshold is unknown, but 50 m may be a good reference. Thus, adding At-Grade Connectors to corner-cuts that come no closer than 50 m to the main roads' intersection junction node is encouraged. Note that in some cases, such as large bowtie junctions, doing so may result in an excessively cluttered and confused display and it is thought better to omit the AGC and tolerate the occasional missing-road Map Problem.
Note that, even if the separation of the turn path from the center of the intersection does not warrant an AGC, an AGC may still be called for to advance the timing of spoken turn alerts as described below.
Advance timing of spoken turn alerts
By advancing the location of the turn on the Waze map, AGCs advance the timing of turn alerts issued to drivers. In most cases the default alert timing is adequate, but in complex situations, advancing the alert may help prevent missed turns. Such situations can include:
- connectors departing from highways of three or more lanes in one direction;
- uncommonly early "commit points" due to extended road striping or physical barriers;
- limited visibility of the upcoming intersection; or
- Update Requests complaining of inadequate alert timing.
Note that, even if inspection suggests no advance of the turn alert is necessary, an AGC may still be warranted to prevent "missing road" errors as described above.
Assessing the need for advanced alerts at complex intersections
When considering an AGC to advance a turn alert at a complex intersection, concern should focus on the penultimate, not the final, voice instruction. Final turn alerts at complex intersections almost always come too late for drivers who missed the previous alerts, and the editing community generally does not modify the maps to accommodate those situations. However, if the penultimate voice instruction would arrive too late for a driver to reach the correct turn lane, that would warrant an AGC for the purpose of advancing the turn alert.
A simple scoring system using "complexity points" can help assess the need for advanced alerts using AGCs. Measure the distance between the intersection junction node and the "commit location" where a driver must commit to a dedicated turn lane, and, for every full 75 m of distance involved, add one point. Then add another point for every lane approaching the intersection (including lanes that become turn lanes, but not any additional turn lanes that appear near the intersection). If the resulting score is four or less, advancing the turn alert is almost certainly unnecessary. If the score is five or more, it is appropriate to advance the turn warning with an AGC. As a rough rule of thumb, the departure junction of the AGC may be moved up by 75 m for every point over four.
The above scoring system is a guideline only. The actual necessity for advancing turn alerts can depend on additional factors such as an uncommonly early commit location (more than 225 m from the intersection), typical traffic load, intersection visibility, and as always, user reports of inadequate alert timing.