From Wazeopedia
== {{@|Big Detours}} ==Waze routing includes 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 mechanism to prevent routing few extra turns, or taking an exit off a highway/freeway only to be routed right back on and then re-entering the same highway/freewaya short distance later. The assumption is that Unless the detours actually save a notable amount of time, they aren't worth it to drivers will prefer , and Waze shouldn't suggest them. Here are two cases where Waze recognizes a detour in the route and applies a penalty to remain on the highway/freeway even if Waze calculates prevent that taking a series of ramps or other collector/distributor roads is slightly faster or shorterdetour unless it saves enough time to be "worth it."
'''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.== {{Anchor|Big Detours}}{{@|Big detours}} ==
The big detour prevention (BDP) is a [[Routing penalties|penalty]] meant to keep Waze from telling you to detour off a highway and then get right back on it unless it saves you enough time to be "worth it" - for example, if traffic is really slow on the "direct" route.
=== {{@|Criteria}} ===;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.
:A {{u|"name-discontinuity"}} is defined as Waze makes a series of segments in middle of a route which do not contain the same name as segments few checks on either side of them in the same route.:Conversely a {{u|"uninterrupted name"}} is defined as a series of segments in middle of a route which an off-highway '''dodetour''' have an identical name on all the segments (with the exception of a single isolated segment among them)to see if it should be prevented.:A {{u|"possible detour"}} is a series of segments in It checks the middle length 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 '''alldetour, ''' makes sure the criteria listed below.  Possible detours are evaluated to determine if they meet ''road type group'ALL''' the following criteriachanges, and are avoided if they do. '''To be considered as a possible detour there must be a Freeway / Highway segment of that the same street name is 'Road Type Group', which share any name, both before and after a series of segments which contain a name-discontinuity, and are in a different not'Road Type Group'continuous with the highway the route detours from.It also checks that there exists an '''alternate route' ''Road type groups are listed in that is direct - the chart below.''#The highway / freeway segments both before and after the possible detour need to have the same (primary, alternate, or any combination of both) street name, which is not present on the name-discontinuity segments. 'direct route'{{As of|2015|June}} city names do not affect this algorithm. While they used to in the past, the algorithm has been updated.''#*The name-discontinuity segments must {{u|not}} have any other uninterrupted street name which appears on both the Fwy/Hwy segments before continuity and after the name-discontinuityroad type group continuity (see details below). Waze does not consider how many 'turn..#There must be an alternate route connecting the Fwy/Hwy segments immediately before and 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 evaluatedkeep..#The first segment after the possible detour must be accessible from another segment of the same road type group.#*''If the first segment after the possible detour is the beginning of the Fwy/Hwy and 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 BDP'exit...''#The possible detour is not composed instructions are issued on any of the same 'Road Type Group' as the continuation after the possible detour.#The name-discontinuity is more than one segment long, and#The possible paths it checks for detour is shorter than the threshold length as defined in the chart belowprevention.
=== {{@|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 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 routes''' that get to that same point 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 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>'''Preventable detour:''' A preventable detour is a possible detour that meets all of these criteria:
<ol style="list-style-type: lower-alpha;"><li>'''Street name discontinuity:''' There must be a break in the '''street name continuity''' between the detour and the bracketing segments. {{As of|February 2018}} only the last segment of the detour is checked. This segment must not share any street names with the highway segment just after the detour (AKA 2nd '''bracketing segment'''). </li>
<li>'''Road type group discontinuity:''' There must be a break in '''road type group''' between the detour and the bracketing segments. {{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 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 '''bracketing segments.'''.</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''', which does not use any of the segments in the detour.</li>
<li>'''Continuity:''' The entire direct route should have '''street name continuity''' and '''road type group continuity'''. {{As of|2017|12}}, this is done with a '''full continuity check''', meaning all segments of the '''alternate route''' must have both road type group and street name continuity with the '''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>
! Road Type Group!! Threshold
| style="border-bottom: 1pt solid #93c4d3;" | {{Freeway}}<br />{{Major Highway}} ||style="border-bottom: 1pt solid #93c4d3;"| 5km
| {{Minor Highway}} || 500m
  It is important [[File:BDP_Flowchart.png|700px|thumb|center|Flowchart Waze Editors can use to check whether Big Detour Prevention Penalty should be applied to understand that Waze uses a [[Routing penaltiesroute|penalty-basedalt=Flowchart of Big Detour Prevention Criteria]] routing system. It computes the total penalties for a route and selects the one with the least cumulative penalty. Therefore it is possible for big detour routes to occur when the primary route is extremely slow.
=== {{@|Notes}} ===
* If the first segment after the detour is the beginning of a freeway or highway, 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.* 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 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 Grouproad type group, preventing BDP from working.
* 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 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).
== {{Anchor|Small Detours}}{{@|Small Detoursdetours}} == 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.