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Detour Prevention Mechanisms

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{{Anchor|Small Detours}}{{@|Small detours}}
Waze searches for the fastest route to the destination, but sometimes, a promising route takes detours from the most obvious, most direct, or otherwise most continuous route. These detours may involve taking side streets, making a few extra turns, or taking an exit off a highway and then re-entering the same highway a short distance later. Unless the detours actually save a notable amount of time, they aren't worth it to drivers, and Waze shouldn't suggest them. Here are two cases where Waze recognizes a detour in the route and applies a penalty to prevent that detour unless it saves enough time to be "worth it."
 
== {{Anchor|Big Detours}}{{@|Big detours}} ==
The big detour prevention (BDP) is a [[Routing penalties|penalty]] (BDP) is meant to keep Waze from telling you to detour off a highway and then get right back on it, even if the detour unless it saves you a little time. Waze should only offer this kind of detour if it saves enough time to be "worth it" - when for example, if traffic is really messed up slow on the "direct" route.
;Direct route :The continuous route most users would expect. For example, a route that stays on the same freeway from point A to point B.;Detour :Any route used in place of the direct route.;Alternate route :What Waze compares a route to - when evaluating a detour route, the direct route is the evaluated alternative.;Road type group continuity :When a set of continuous segments all belong to the same road type group (see table below), there is '''road type group continuity'''. '''Road type group discontinuity ''' occurs when one of the segments in the set of continuous segments belongs to a different road type group.;Street name continuity :When a set of continuous segments all share a street name, there is '''street name continuity'''. It doesn't matter whether the street name is found as a primary or alternate name on any of the segments, as long as it is present in each. For the purposes of detour prevention, only the name of the street itself must match. The city name can be different, and it will still be considered continuous. '''Street name discontinuity''' occurs when one or more of the segments in this continuous set does not share the street name shared by all the other segments.  Waze makes a few checks on an off-highway '''detour ''' to see if it should be prevented. It checks the length of the '''possible detour, '''makes sure the ''road typegroup'' changes, and that the street name is ''not'' continuous with the highway you are detoured the route detours from. It also checks that there exists an '''alternate route''' that is direct - the '''direct route''' must have both continuous street name continuity and road type and name group continuity(see details below). Waze does not consider how many 'turn...', 'keep...', or 'exit...' instructions are issued on any of the paths it checks for detour prevention.
=== {{@|Criteria}} ===
A If a '''possible detour''' is one we are checking. If it being examined passes these the checkslisted below, we'll call it a '''confirmed preventable detour. '''An If a route leaves a highway (based on road group 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 routeroutes''' is one we are checking that get to that same point try to see if it is find a '''direct route'''. ''' '''If there is a '''direct route'''is found, then Waze will apply the big detour prevention (BDP) [[Routing penalties|penalty ]] to the '''confirmed preventable detour'''favoring the''' direct route'''. Here are the specific checks that Waze makes:<ol style="list-style-type: upper-roman;"><li>'''Segments Bracketing segments''' '''(segment immediately before and immediately after the possible 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(city names are not required to match). Either segment may have the shared street 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 group of these segments determines the maximum length of detour for which BDP will be applied. </li><li>'''Confirmed Preventable detour:''' A confirmed preventable detour is a a possible detour that meets all of these criteria: <ol style="list-style-type: lower-alpha;"><li>'''Name Street name discontinuity - :'''The possible detour There must have at least one be a break in the '''street name continuity from the last segment before ''' between the detour to and the first segment after the detourbracketing segments. Specifically, {{As of|February 2018}} only the last segment of the possible detour is checked. This segment must not have name continuity share any street names with the first highway segment just after the possible detour(AKA 2nd '''bracketing segment''').</li> <li>'''Road type group discontinuity:''' - The possible detour There must include at least one segment not be a break in the same '''road type group '''as between the detour and the bracketing segments immediately before and . {{As of|February 2018}} only the last segment of the detour is checked. This segment must have a different road type group than the highway segment just afterthe 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>
<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 used in the possible detour.</li><li>'''Continuity:''' The entire alternate direct route should have '''street name continuity''' and '''road type group continuity. In the past, less resource-intensive methods have been used for checking the direct route'''. {{As of|2017|12}} , this is done with a '''full continuity check''' is in use. All , meaning all segments of the '''alternate route ''' must have both road type group and street name and type continuity with the segment immediately before and the segment immediately after the possible 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>
</li>
</ol>
| {{Minor Highway}} || 500m
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[[File:BDP_Flowchart.png|700px|thumb|center|Flowchart Waze Editors can use to check whether Big Detour Prevention Penalty should be applied to a route|alt=Flowchart of Big Detour Prevention Criteria]]
=== {{@|Notes}} ===
* If the first segment after the possible detour is the beginning of a freeway or highway then the first segment , and, thus, can only be accessed from ramps or segments of a different road type group, then there can be no direct route according to the above criteria above.*For divided roadways that have the same street name on both carriageways, the big detour prevention mechanism will prevent U-turns that traverse more than one segment. Thus , in the intersection below, the configuration on the left will should be used to route a U-turn because it uses a single segment between the two parallel roadways with the same name. In contrast, the configuration on the right will '''should not''' use be used because the U-turn road because it branches from another segment causing multiple segments between the two parallel roads with the same name, and the U-turn is not in the same road type group, preventing BDP from working.
[[File:UDetour.png|border|center]]
* Be careful of "false positives!" For example, where route number concurrencies concurrences begin and end, the big detour prevention mechanism may be unexpectedly triggered as follows (see diagram):** In a concurrency, two highways share the same road, and both street names will appear on the concurrent segments, using [[alternate names]]. Where the concurrency ends, the two highways split into separate roadways again.** Often, there are ramp segments connecting the last concurrent segment to one or both of the non-concurrent continuations. If the concurrency was of I-1234 and I-4567, for example, there might be a ramp named "to I-1234 / Sometown" - a street name which contains "I-1234" but is not identical to the highway name.
** If the ramp does not also carry a simple alternate name of "I-1234", then there is a discontinuity of the highway name between the concurrency and the continuation highway. If there are two ramp segments like this, it will trigger Big Detour Prevention unexpectedly, and Waze will create an unneeded penalty for continuing on I-1234.
** To prevent this, just assign I-1234 as an alternate street name to all ramps between the two sections (concurrency and continuation). Note that if there is only a single ramp segment connecting the highways, there will not be a "false positive." Nevertheless, it is a good practice to do this even for a single ramp segment, in case the ramp is cut into two segments later, either by accident or because later construction or map improvements connect another feeder ramp in the middle.
* Another example of a false positive could occur where a highway has multiple wayfinders connected , one to another , (for example, if there are several multi-lane exits in a row).
[[File:AltNameDetour.jpg|border|center]]
== {{Anchor|Small Detours}}{{@|Small detours}} ==
 Waze has a small detour prevention (SDP) mechanism to deal with instances where Waze calculates that that a left turn can be "optimized" by using U-turns and right turns (either continue straight, U-turn, right turn; or alternatively, immediate right turn, U-turn, continue straight). While this may save a few seconds over waiting for a long average left turn, it is undesirable. Waze will prevent such detours if there is not a measurable notable difference in the route times. The exact actual difference in time required to trigger this prevention is proprietarya closely-guarded secret, and subject but if you come across one of these where you feel Waze didn't adequately prevent it, please contact your community leadership for advice. There may still be a solution, but it may have to change as neededbe evaluated on a case-by-case basis.
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