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Detour Prevention Mechanisms

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Moved User:CBenson/Detour_Prevention_Mechanisms here as discussed here: https://www.waze.com/forum/viewtopic.php?f=276&t=171696
== {{@|Big Detours}} ==
Waze routing includes a big detour prevention (BDP) mechanism to prevent routing off a highway/freeway only to be routed right back on the same highway/freeway. The assumption is that drivers will prefer to remain on the highway/freeway even if Waze calculates that taking a series of ramps or other collector/distributor roads is slightly faster or shorter. '''NOTE:''' The continuation path we wish Waze to use must not also meet the below criteria, or it will be equally penalized, cancelling the BDP effect. 
=== {{@|Criteria}} ===
:A {{u|"name-discontinuity"}} is defined as a series of segments in middle of a route which do not contain the same name as segments on either side of them in the same route.
:Conversely an {{u|"uninterrupted name"}} is defined as a series of segments in middle of a route which '''do''' have an identical name on all the segments (with the exception of a single isolated segment among them).
:A {{u|"possible detour"}} is a series of segments in the middle of a route which meet the minimum criteria to trigger an evaluation.
:A {{u|"detour"}} is defined as a portion of a route which meets '''all''' the criteria listed below.
Possible detours are evaluated to determine if they meet '''ALL''' the following criteria, and are penalized if they do.
'''NOTE:''' If the continuation path we wish Waze to use also meets the below criteria it will be equally penalized, cancelling the BDP effect.
Possible detours are evaluated to determine if they meet #'''ALLRoad Name Discontinuity''' - The freeway/highway segments immediately before and immediately after the possible detour must share at least one street name (either segment may have the following criteria, and are avoided if they do. '''To be considered shared name as either a primary or an alternate name). {{u|The possible detour there must be a Freeway / Highway include at least one segment (including the last segment of the same possible detour) that is missing this shared street name (as both a primary name and alternate names).}}##No Other Continuous Name - {{u|The possible detour segments must ''not'Road Type Group', which all share any other street name, with the both the freeway/highway segments immediately before and immediately after a series of segments which contain a name-discontinuity, and are in a different 'Road Type Group'the possible detour.}}#''' Road Type Discontinuity''Road type groups are listed in the chart below.''#- The freeway/highway / freeway segments both immediately before and immediately after the possible detour need to have must be from the same (primary, alternate, or any combination of both) street name, which is not present on 'Road Type Group' as defined in the name-discontinuity segmentschart below. '' {{As ofu|2015|JuneThe possible detour must include at least one segment not in that same 'Road Type Group.'}} city names do not affect this algorithm#'''Existence Of Direct Route''' - The BDP mechanism is intended to penalize detours away and back to a direct route. While they The following two criteria are used to in the past, the algorithm has been updateddetermine if there may be a possible direct route.''#*The name#Existence Of Alternate Route -discontinuity segments must {{u|not}} have any other uninterrupted name which appears on both the Fwy/Hwy segments before and after the name-discontinuity.#There must be an alternate route connecting the Fwyfreeway/Hwy highway segments immediately before and immediately after the possible detour which bypasses the segments of the possible detour.}}#*This alternative route may also be a detour itself, as long as it is a different route and doesn't use the same segments as the original possible detour being evaluated.#Alternate Road Type Continuity - {{u|The first freeway/highway segment immediately after the possible detour must be accessible from another segment of the same road type group.}}#*''The BDP mechanism does not determine that there is actually a direct route with name and type continuity, but rather only uses the above two criteria. #*''Thus, the alternate route may be a detour itself. The alternate route need only use different segments than the possible detour being evaluated.#*''If the first segment after the possible detour is the beginning of the Fwy/Hwy a freeway or highway and , thus, can only be accessed from ramps, or segments of a different road type group, it will not be considered a part of a Fwy/Hwy continuation - thereby cancelling BDPis assumed that there is no direct route.''#The possible detour is not composed of the same 'Road Type Group' as the continuation after the 'Minimum Length''' - {{u|The possible detour.#The name-discontinuity is must be more than one segment long, and.}}#'''Maximum Length''' - {{u|The possible detour is must be shorter than the threshold length as defined in the chart below.}}
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