Difference between revisions of "User:Nagamasa/Junction box"

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(Created page with "==When to use== Junction boxes are suitable only for specific locations where the above-listed functions of junction boxes are required. An example would be to prohibit the U-...")
 
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Appropriate times to use a junction box:
 
Appropriate times to use a junction box:
* Have two entrances to same exit path but one route is prohibited so can't use a simple Turn restriction
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* To allow routes across multiple junction nodes:
* Have u-turn allowed in one direction of an H-intersection, but prohibited in another
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** Where there can be two entrances to same exit path, but a route is prohibited. A simple turn restriction cannot adequately set the correct restrictions.
* To override u-turn prevention when the cross segment is less than {{:Routing_penalties/U-turn_minimum|less}} due to the geometry of the intersections
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** In an H-intersection, when u-turns are allowed in one direction, but prohibited in the opposite direction.
* Traffic backs up through multiple junction nodes from a direct left turn, an at-grade connector (AGC), an exit ramp, or even through travel caught at a traffic light; where the back up adversely affects the timing for the traffic that is moving
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** When the cross segment is less than {{:Routing_penalties/U-turn_minimum|less}} due to the geometry of the intersection, and u-turn prevention needs to be overwritten to allow u-turns.
* To better collect traffic data on intricate intersections
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* To set a turn instruction override in these situations:
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** A single turn instruction at the first junction node, and no additional instructions for a route.
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** To advance an
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* To better collect traffic data when there is a speed differential between various traffic lanes through multiple junction nodes, such as:
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** At-grade connectors (AGC) and parking lot roads cutting an intersection into multiple segments and nodes
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** Auxiliary lanes: entry ramps that extend to the next exit ramp: drivers that are merging on/off the freeway will have a different set of speeds than those that were already on the freeway and continuing on it
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** Regular, long backups: backups that extend past turn pockets and the exit ramp
  
  

Revision as of 19:00, 24 May 2019

When to use

Junction boxes are suitable only for specific locations where the above-listed functions of junction boxes are required. An example would be to prohibit the U-turn in one direction but allow it in the other such that a 45.93 ft (14 m) center segment is forcing a necking down of the normal flow of a road and micro-doglegs are used to allow the one direction's U-turn. If problems with data collection or turn restrictions are experienced then, a junction box may be used to solve the problem. If problems are easily solved with other features such as turn restrictions, then a junction box should not be used. For routes through H intersections that have one u-turn allowed and one u-turn prevented then use a simple junction box instead of or U-turn penalties and using micro doglegs to break the u-turn prevention in one direction. Existing intersections with micro doglegs or abnormal geometry can be changed to a junction box when being edited for other reasons, but you shouldn't go out hunting to eliminate all of them if they are already working properly.

Appropriate times to use a junction box:

  • To allow routes across multiple junction nodes:
    • Where there can be two entrances to same exit path, but a route is prohibited. A simple turn restriction cannot adequately set the correct restrictions.
    • In an H-intersection, when u-turns are allowed in one direction, but prohibited in the opposite direction.
    • When the cross segment is less than 45.93 ft (14 m) due to the geometry of the intersection, and u-turn prevention needs to be overwritten to allow u-turns.
  • To set a turn instruction override in these situations:
    • A single turn instruction at the first junction node, and no additional instructions for a route.
    • To advance an
  • To better collect traffic data when there is a speed differential between various traffic lanes through multiple junction nodes, such as:
    • At-grade connectors (AGC) and parking lot roads cutting an intersection into multiple segments and nodes
    • Auxiliary lanes: entry ramps that extend to the next exit ramp: drivers that are merging on/off the freeway will have a different set of speeds than those that were already on the freeway and continuing on it
    • Regular, long backups: backups that extend past turn pockets and the exit ramp


Junction boxes create another limitation that should be considered:

  • Segments connected to junction boxes have some attributes that cannot be edited without first deleting the junction box.


Edits not allowed are:

  • Direction of travel (two way/one way)
  • Turn restrictions that are not in the junction box for segments that extend outside the junction box's boundaries
  • Moving the location of a junction node within a junction box
  • Edits that change a segment's identification number
  1. Adding or deleting a junction node inside the junction box
  2. Adding or deleting a junction node on a segment that extends outside the junction box (ex. You have to delete the junction box to add a parking lot road to a segment that is included in a junction box)


For these reasons, junction boxes should not be used for every intersection.