From Wazeopedia

Detour Prevention Mechanisms

2,017 bytes added, 2 years ago
Big detours: Updated some language to hopefully make this sound less technical and more streamlined.
Waze searches for the best route to the destination, depending on your navigation strategy. In Waze, this is either the fastest route or the shortest route, as set in the app settings. Sometimes, it might find detours from the most obvious, most direct, or otherwise most continuous route. These detours may involve taking side streets and making a few extra turns or an exit off a highway only to re-enter the same highway a short distance later. Unless the detours actually save a notable amount of time and are said to be "worth it," Waze shouldn't suggest them. Here are two cases where Waze should recognize a detour in the route and prevent it unless the detour actually does save a notable amount of time and is "worth it."
== {{Anchor|Big Detours}}{{@|Big detours}} ==
The big detour [[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 saves you a little , often trivial, amount of 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 backed up 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.
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 type'' changes, and that the 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 road type and name continuity, which is described in further detail 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 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 to see if it is that re-entered highway segment and try to find a '''direct route'''. ''' '''If there is a '''direct route'''is found, then Waze will apply the big detour [[Routing penalties|penalty ]] (BDP) to the '''confirmed preventable detour''', thus favoring the''' direct route'''. Here are the specific checks that Waze makes:<ol style="list-style-type: upper-roman;"><li>'''Segments before and after the possible detour:''' The freeway/highway 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 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 possible detour that meets all of these criteria: <ol style="list-style-type: lower-alpha;"><li>'''Name discontinuity - '''The possible detour must have at least one break segment that has no names in name continuity from common with any of the names on the highway the route left and is re-entering after a short distance, including the last highway segment right before the start of the detour to and the first highway segment immediately after the detour. Specifically, the last segment end of the possible detour must not have . This condition is said to be a break in "name continuity with the first segment after " of the possible detour.</li> <li>'''Road type discontinuity''' - The possible detour must include have at least one segment whose road type is not in the same '''road type group '''as the segments highway the route left and is re-entering, including the highway segment immediately before the start of the detour and the highway segment immediately afterthe end of the detour. This condition is said to be a break in "road type continuity" of the detour.</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 segments immediately before and after the detour.</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 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 route should have name and road type 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 name and type continuity with the segment immediately before and the segment immediately after the possible detour. 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>
=== {{@|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 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.
* 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 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 name which contains "I-1234" but is not identical to the highway name.
** To prevent this, just assign I-1234 as an alternate 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 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, but if you come across one of these where you feel Waze didn't adequately prevent it, and subject 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.