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Detour Prevention Mechanisms

1 byte removed, 1 year ago
Criteria: Added "bracketing segments" throughout criteria.
=== {{@|Criteria}} ===
If a '''detour''' being examined passes the checks listed below, we'll call it a '''preventable detour. '''If a route leaves a highway (based on road type) to one or more segments whose road type is not in the same '''road type group''' as the highway, only to re-enter that same highway, Waze will look for '''alternate routes''' to that re-entered highway segment and try to find a '''direct route'''.''' '''If a '''direct route '''is found, then Waze will apply the big detour prevention (BDP) [[Routing penalties|penalty]] to the '''preventable detour '''favoring the''' direct route'''. Here are the specific checks that Waze makes:
<ol style="list-style-type: upper-roman;"><li>'''Bracketing Segments ''' '''(segment immediately before and immediately after the detour):''' The freeway/highway bracketing segments immediately before and immediately after the possible detour must share at least one street name among their primary and alternate names. Either segment may have the shared name as either a primary or an alternate name. These segments must also be from the same '''road type group''' as shown in the table below. The road type of these segments determines the maximum length of detour for which BDP will be applied. </li>
<li>'''Preventable detour:''' A preventable detour is a possible detour that meets all of these criteria:
<ol style="list-style-type: lower-alpha;"><li>'''Name discontinuity''' - There must be a break in the '''name continuity''' of the detour. {{As of|February 2018}} only the last segment of the detour is checked. This segment must not share any names with the highway segment just after the detour(AKA 2nd '''bracketing segment'''). </li> <li>'''Road type discontinuity''' - There must be a break in '''road type continuity'''. {{As of|February 2018}} only the last segment of the detour is checked. This segment must have a different road type than the highway segment just after the detour(AKA 2nd '''bracketing segment''').</li>
<li>'''Minimum length''' - The possible detour must be more than one segment long.</li>
<li>'''Maximum length''' - The possible detour must be shorter than the threshold length as shown in the table below for the road type group of the two '''bracketing segments immediately before and after the detour.'''.</li>
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<li>'''Direct route:''' A direct route is an alternate route that meets the criteria below:
<ol style="list-style-type: lower-alpha;"><li>'''Existence''': There must be a different way to go - an '''alternate route ''' - connecting the freeway/highway '''bracketing segments immediately before and immediately after the detour''', which does not use any of the segments in the detour.</li><li>'''Continuity''' The entire alternate route should have '''name continuity''' and '''road type continuity'''. {{As of|2017|12}}, this is done with a '''full continuity check''', meaning all segments of the '''alternate route ''' must have both name and type continuity with the segment immediately before and the segment immediately after the detour'''bracketing segments'''. This is the most resource-intensive continuity check, but is also the most robust way to to help ensure we don't penalize routes unless there actually is a comparable route that doesn't involve changing roads at all. </li></ol>
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