[GTFS-Fares v2] Add networks.txt & route_networks.txt (#405)

* Add networks.txt & route_networks.txt

* Modify presence of routes.network_id

Changed to Conditionally Forbidden

* Modify fare_leg_rules.network_id

* Modify primary key of route_networks.txt

* Revise link

gtfs/spec/en/reference.md

@@ -26,6 +26,8 @@ This document defines the format and structure of the files that comprise a GTFS
     -   [fare\_transfer\_rules.txt](#fare_transfer_rulestxt)
     -   [areas.txt](#areastxt)
     -   [stop_areas.txt](#stop_areastxt)
+    -   [networks.txt](#networkstxt)
+    -   [route_networks.txt](#route_networkstxt)
     -   [shapes.txt](#shapestxt)
     -   [frequencies.txt](#frequenciestxt)
     -   [transfers.txt](#transferstxt)
@@ -119,6 +121,8 @@ This specification defines the following files:
 |  [fare_transfer_rules.txt](#fare_transfer_rulestxt)  | Optional | Fare rules for transfers between legs of travel.<br><br>Along with [fare_leg_rules.txt](#fare_leg_rulestxt), file [fare_transfer_rules.txt](#fare_transfer_rulestxt) provides a more detailed method for modeling fare structures. As such, the use of [fare_transfer_rules.txt](#fare_transfer_rulestxt) is entirely separate from files [fare_attributes.txt](#fare_attributestxt) and [fare_rules.txt](#fare_rulestxt). |
 |  [areas.txt](#areastxt) | Optional | Area grouping of locations. |
 |  [stop_areas.txt](#stop_areastxt) | Optional | Rules to assign stops to areas. |
+|  [networks.txt](#networkstxt) | **Conditionally Forbidden** | Network grouping of routes.<br><br>Conditionally Forbidden:<br>- **Forbidden** if `routes.network_id` field exists.<br>- Optional otherwise. |
+|  [route_networks.txt](#route_networkstxt) | **Conditionally Forbidden** | Rules to assign routes to networks.<br><br>Conditionally Forbidden:<br>- **Forbidden** if `routes.network_id` field exists.<br>- Optional otherwise. |
 |  [shapes.txt](#shapestxt)  | Optional | Rules for mapping vehicle travel paths, sometimes referred to as route alignments. |
 |  [frequencies.txt](#frequenciestxt)  | Optional | Headway (time between trips) for headway-based service or a compressed representation of fixed-schedule service. |
 |  [transfers.txt](#transferstxt)  | Optional | Rules for making connections at transfer points between routes. |
@@ -224,7 +228,7 @@ Primary key (`route_id`)
 |  `route_sort_order` | Non-negative integer | Optional | Orders the routes in a way which is ideal for presentation to customers. Routes with smaller `route_sort_order` values should be displayed first. |
 |  `continuous_pickup` | Enum | Optional | Indicates that the rider can board the transit vehicle at any point along the vehicle’s travel path as described by `shapes.txt`, on every trip of the route. Valid options are: <br><br>`0` - Continuous stopping pickup. <br>`1` or empty - No continuous stopping pickup. <br>`2` - Must phone agency to arrange continuous stopping pickup. <br>`3` - Must coordinate with driver to arrange continuous stopping pickup.  <br><br>Values for `routes.continuous_pickup` may be overridden by defining values in `stop_times.continuous_pickup` for specific `stop_time`s along the route. |
 |  `continuous_drop_off` | Enum | Optional | Indicates that the rider can alight from the transit vehicle at any point along the vehicle’s travel path as described by `shapes.txt`, on every trip of the route. Valid options are: <br><br>`0` - Continuous stopping drop off. <br>`1` or empty - No continuous stopping drop off. <br>`2` - Must phone agency to arrange continuous stopping drop off. <br>`3` - Must coordinate with driver to arrange continuous stopping drop off. <br><br>Values for `routes.continuous_drop_off` may be overridden by defining values in `stop_times.continuous_drop_off` for specific `stop_time`s along the route. |
-| `network_id` | ID | Optional | Identifies a group of routes. Multiple rows in [routes.txt](#routestxt) may have the same `network_id`.| 
+| `network_id` | ID | **Conditionally Forbidden** | Identifies a group of routes. Multiple rows in [routes.txt](#routestxt) may have the same `network_id`.<br><br>Conditionally Forbidden:<br>- **Forbidden** if `route_networks.txt` file exists.<br>- Optional otherwise. 
 
 ### trips.txt
 
@@ -450,7 +454,7 @@ To process the cost of a leg:
 |  Field Name | Type | Presence | Description |
 |  ------ | ------ | ------ | ------ |
 | `leg_group_id` | ID | Optional | Identifies a group of entries in [fare_leg_rules.txt](#fare_leg_rulestxt).<br><br> Used to describe fare transfer rules between `fare_transfer_rules.from_leg_group_id` and `fare_transfer_rules.to_leg_group_id`.<br><br>Multiple entries in [fare_leg_rules.txt](#fare_leg_rulestxt) may belong to the same `fare_leg_rules.leg_group_id`.<br><br>The same entry in [fare_leg_rules.txt](#fare_leg_rulestxt) (not including `fare_leg_rules.leg_group_id`) must not belong to multiple `fare_leg_rules.leg_group_id`.|
-| `network_id` | Foreign ID referencing `routes.network_id` | Optional | Identifies a route network that applies for the fare leg rule.<br><br>If there are no matching `fare_leg_rules.network_id` values to the `network_id` being filtered, empty `fare_leg_rules.network_id` will be matched by default.<br><br> An empty entry in `fare_leg_rules.network_id` corresponds to all networks defined in `routes.txt` excluding the ones listed under `fare_leg_rules.network_id` |
+| `network_id` | Foreign ID referencing `routes.network_id` or `networks.network_id`| Optional | Identifies a route network that applies for the fare leg rule.<br><br>If there are no matching `fare_leg_rules.network_id` values to the `network_id` being filtered, empty `fare_leg_rules.network_id` will be matched by default.<br><br> An empty entry in `fare_leg_rules.network_id` corresponds to all networks defined in `routes.txt` or `networks.txt` excluding the ones listed under `fare_leg_rules.network_id` |
 | `from_area_id` | Foreign ID referencing `areas.area_id` | Optional | Identifies a departure area.<br><br>If there are no matching `fare_leg_rules.from_area_id` values to the `area_id` being filtered, empty `fare_leg_rules.from_area_id` will be matched by default. <br><br>An empty entry in `fare_leg_rules.from_area_id` corresponds to all areas defined in `areas.area_id` excluding the ones listed under `fare_leg_rules.from_area_id` |
 | `to_area_id` | Foreign ID referencing `areas.area_id` | Optional | Identifies an arrival area.<br><br>If there are no matching `fare_leg_rules.to_area_id` values to the `area_id` being filtered, empty `fare_leg_rules.to_area_id` will be matched by default.<br><br> An empty entry in `fare_leg_rules.to_area_id` corresponds to all areas defined in `areas.area_id` excluding the ones listed under `fare_leg_rules.to_area_id` |
 |  `from_timeframe_group_id` | Foreign ID referencing `timeframes.timeframe_group_id` | Optional |  Defines the timeframe for the fare validation event at the start of the fare leg.<br><br>The “start time” of the fare leg is the time at which the event is scheduled to occur.  For example, the time could be the scheduled departure time of a bus at the start of a fare leg where the rider boards and validates their fare. For the rule matching semantics below, the start time is computed in local time, as determined by [Local Time Semantics](#localtimesemantics) of [timeframes.txt](#timeframestxt).  The stop or station of the fare leg’s departure event should be used for timezone resolution, where appropriate.<br><br>For a fare leg rule that specifies a `from_timeframe_group_id`, that rule will match a particular leg if there exists at least one record in `timeframes.txt` where all of the following conditions are true<br>- The value of `timeframe_group_id` is equal to the `from_timeframe_group_id` value.<br>- The set of days identified by the record’s `service_id` contains the “current day” of the fare leg’s start time.<br>- The “time-of-day” of the fare leg's start time is greater than or equal to the record’s `timeframes.start_time` value and less than the `timeframes.end_time` value.<br><br>An empty `fare_leg_rules.from_timeframe_group_id` indicates that the start time of the leg does not affect the matching of this rule. |
@@ -519,6 +523,32 @@ Assigns stops from [stops.txt](#stopstxt) to areas.
 | `area_id` | Foreign ID referencing `areas.area_id` | **Required** | Identifies an area to which one or multiple `stop_id`s belong. The same `stop_id` may be defined in many `area_id`s. |
 | `stop_id` | Foreign ID referencing `stops.stop_id` | **Required** | Identifies a stop. If a station (i.e. a stop with `stops.location_type=1`) is defined in this field, it is assumed that all of its platforms (i.e. all stops with `stops.location_type=0` that have this station defined as `stops.parent_station`) are part of the same area. This behavior can be overridden by assigning platforms to other areas. |
 
+### networks.txt
+
+File: **Conditionally Forbidden**
+
+Primary key (`network_id`)
+
+Defines network identifiers that apply for fare leg rules. Forbidden if `routes.network_id` field exists.
+
+|  Field Name | Type | Presence | Description |
+|  ------ | ------ | ------ | ------ |
+| `network_id` | Unique ID | **Required** | Identifies a network. Must be unique in [networks.txt](#networkstxt). |
+| `network_name` | Text | **Optional** | The name of the network that apply for fare leg rules, as used by the local agency and its riders.
+
+### route_networks.txt
+
+File: **Conditionally Forbidden**
+
+Primary key (`route_id`)
+
+Assigns routes from [routes.txt](#routestxt) to networks. Forbidden if `routes.network_id` field exists.
+
+|  Field Name | Type | Presence | Description |
+|  ------ | ------ | ------ | ------ |
+| `network_id` | Foreign ID referencing `networks.network_id` | **Required** | Identifies a network to which one or multiple `route_id`s belong. A `route_id` can only be defined in one `network_id`. |
+| `route_id` | Foreign ID referencing `routes.route_id` | **Required** | Identifies a route. |
+
 ### shapes.txt
 
 File: **Optional**