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Junction Style Guide/Interchange

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Collector/distributor interchanges
The two surface street segments (between the outer ramps and connected to the Single Point) and the 4 ramp segments connected to the single point should all be the same level, either one higher or one lower than the elevation of the freeway segments above/below the single point.
=== Collector/distributor interchanges lanes ===
These are lanes parallel to , but physically separated from , the lanes of a Limited Access Road Freeway that serve to keep merging traffic out of the flow of through traffic on the mainline Freeway.
==== Collector/distributor cloverleaf ====lanes serve as either:* some of the ramps in an '''interchange''', or* local lanes in configurations with '''[[wikipedia:local-express lanes|local-express lanes]]'''.
This is a Cloverleaf interchange that is connected to a Collector/Distributor instead of directly to the main roadway. Here is an example which matches the physical world but has a major deficiency.
[[Image:Jct_fc_cloverleaf_bad.png]]==== Collector/distributor interchanges ====
At first it appears that this layout allows everyone Some interchange configurations make use of collector/distributor lanes to get where they are going. The problem is that it allows MORE than it shouldseparate lower-speed merging traffic from high-speed through traffic. It This is possible to exit the mainline Freeway and stay on the Collector/Distributor, bypassing the Cloverleaf, often used in cloverleaf interchanges and merge back onto the mainline Freewayin groups of nearby exits.
Although this may be a way to avoid traffic on the mainline Freeway, doing so is inefficient, may be unsafe, and is outright illegal in some areas. Therefore we need to tweak our design a little...===== Collector/distributor cloverleaf =====
[[Image:Jct_fc_cloverleaf_goodThis is a cloverleaf interchange that is connected to a collector/distributor instead of directly to the main roadway. Map collector-distributor cloverleaf ramps as you would any other ramp.png]]
In this example, we have eliminated the ramp segment joining the two loops of the cloverleaf and the Collector/Distributor ramps. Now they all connect at a single point and we are therefore able to restrict the turn that allowed drivers to use the Collector/Distributor as a bypass. ==== Complex collector/distributor ==== A Collector/Distributor is considered complex if there are multiple exits and entrances connected to the Collector/Distributor[[Image:Jct_fc_cloverleaf_bad.png]]
Ideally you The [[Detour Prevention Mechanisms|detour prevention mechanism]] will '''not''' have to implement any of prevent Waze from routing users onto the collector-distributor and back onto the complex layouts described in freeway. Previously this section. Start by representing feature was not available and the ramps in were set up to restrict the simplest manner possible and see how they perform for a whilethrough route. If everything is mapped correctly and navigation Some of these ramp configurations may still tries to have drivers bypass the mainline Freewaybe set up that way, then and only then modify the layout so they can now be configured as pictured above with the following suggestionsthrough route enabled.
If we are lucky, we can still restrict the bypass movement with the single central node like we did for the [[#Collector.2FDistributor_Cloverleaf|Collector==== Complex collector/Distributor Cloverleaf]] example. Notice how all the exits are either before or at the central node (highlighted in the next image) and all the entrances are at or after the central node.distributor interchanges ====
[[Image:Jct_cmplx_collector_1Collector-distributor-exit.png|thumb|right|450px|Collector-distributor lanes used in an interchange on I-81 in Christiansburg, Virginia (Exits 118A-B-C)]]
It becomes more complicated if entrances and exits Where collector/distributor lanes are more mixed. In the following exampleused as part of an interchange, there is an entrance before an exit and use the highlighted path shows this entering traffic crossing {{Ramp}} type for the exiting traffic we dealt with in previous examplescollector/distributor lanes. If we use the same restricted turn on Name the same node ramp segments as in previous examples, we block traffic entering from the right-most entrance from being able to get to the mainline Freeway. If we enable that turn, now we are no longer blocking the bypass movementyou would any other ramp segment.
[[Image:Jct_cmplx_collector_2a.png]]{{clear}}
To get the control we require, we need to run the entrance ramp up to the node of the last exit. This allows the exiting traffic to be kept separate from the entering traffic. In the next example, we have modified the right==== Local-most entrance so it connects further down the Collector/Distributor. Even if the Collector/Distributor itself is only one lane, we want to have these parallel road segments through the area. They can be close together, but do not overlap them. You will have segments overlapping, but be sure not to junction them together.express lanes ====
[[Image:Jct_cmplx_collector_2bLocal-express.png|thumb|right|450px|A local-express lane configuration on I-96 in Livonia, Michigan]]
Now we can restrict Local-express lanes are similar to collector/distributor interchange, but on a larger scale. While collector/distributor interchanges typically have an exit number or numbers, local-express lanes typically share the exiting traffic from using same name, differentiated by "Local" for the Collectorcollector/Distributor as a bypass of the mainline Freeway as we have previously without impacting distributor lanes and "Express" for the entering trafficthru lanes.
In a more complicated caseA local-express lane configuration is not technically an "interchange"; however, you will need since its physical characteristics are similar to create parallel paths for exiting and entering traffic for those of a majority of the Collectorcomplex collector/Distributor's length. In the following exampledistributor interchange, the path for exiting traffic is highlighted and the ramps available for entering traffic appear normally. There is no mixing of entering and exiting traffic in this logical view of the Collector/Distributor even if traffic it is mixing in realitydiscussed here.
Where collector/distributor lanes are used as part of a local-express lane configuration,*use the same type (most likely {{Freeway}}) for the Local lanes as is used for the Express lanes, and*name the road as it is signed: typically "[Name] Local [ImageDirection]":Jct_cmplx_collector_3for example, "I-96 Local W" (and "I-96 Express W" for the Express lanes).png]]
As a worse case scenario, you may have a situation where traffic can enter early in the Collector/Distributor and can legally exit at any of the exits along the Collector/Distributor. In this case you will need to carefully create junctions with restricted turns or even additional ramps to enable the legal movements.{{clear}}
== See also ==
Review the [http://en.wikipedia.org/wiki/Interchange_(road) Wikipedia article on Road Interchanges] for further information on this topic.
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