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<ol class="chapter"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.</strong> Overview</a></li><li class="chapter-item expanded "><a href="../howto/index.html"><strong aria-hidden="true">2.</strong> Instructions</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../howto/map_parking.html"><strong aria-hidden="true">2.1.</strong> How to map on-street parking</a></li><li class="chapter-item expanded "><a href="../howto/new_city.html"><strong aria-hidden="true">2.2.</strong> Importing a new city</a></li></ol></li><li class="chapter-item expanded "><a href="../how_it_works.html"><strong aria-hidden="true">3.</strong> How it works</a></li><li class="chapter-item expanded "><a href="../case_studies/index.html"><strong aria-hidden="true">4.</strong> Case studies</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../case_studies/lake_wash.html"><strong aria-hidden="true">4.1.</strong> Lake Washington Blvd Stay Healthy Street</a></li><li class="chapter-item expanded "><a href="../case_studies/west_seattle.html"><strong aria-hidden="true">4.2.</strong> West Seattle mitigations</a></li><li class="spacer"></li></ol></li><li class="chapter-item expanded "><a href="../dev/index.html"><strong aria-hidden="true">5.</strong> Developer guide</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../dev/misc_tricks.html"><strong aria-hidden="true">5.1.</strong> Misc developer tricks</a></li><li class="chapter-item expanded "><a href="../dev/api.html"><strong aria-hidden="true">5.2.</strong> API</a></li><li class="chapter-item expanded "><a href="../dev/testing.html"><strong aria-hidden="true">5.3.</strong> Testing</a></li><li class="chapter-item expanded "><a href="../dev/mass_import.html"><strong aria-hidden="true">5.4.</strong> Importing many maps</a></li><li class="chapter-item expanded "><a href="../dev/data.html"><strong aria-hidden="true">5.5.</strong> Data organization</a></li></ol></li><li class="chapter-item expanded "><a href="../map/index.html"><strong aria-hidden="true">6.</strong> Map model</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../map/details.html"><strong aria-hidden="true">6.1.</strong> Details</a></li><li class="chapter-item expanded "><a href="../map/importing/index.html"><strong aria-hidden="true">6.2.</strong> Importing</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../map/importing/convert_osm.html"><strong aria-hidden="true">6.2.1.</strong> convert_osm</a></li><li class="chapter-item expanded "><a href="../map/importing/geometry.html"><strong aria-hidden="true">6.2.2.</strong> Road/intersection geometry</a></li><li class="chapter-item expanded "><a href="../map/importing/rest.html"><strong aria-hidden="true">6.2.3.</strong> The rest</a></li><li class="chapter-item expanded "><a href="../map/importing/misc.html"><strong aria-hidden="true">6.2.4.</strong> Misc</a></li></ol></li><li class="chapter-item expanded "><a href="../map/edits.html"><strong aria-hidden="true">6.3.</strong> Live edits</a></li><li class="chapter-item expanded "><a href="../map/platform.html"><strong aria-hidden="true">6.4.</strong> Exporting</a></li></ol></li><li class="chapter-item expanded "><a href="../trafficsim/index.html"><strong aria-hidden="true">7.</strong> Traffic simulation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trafficsim/discrete_event.html"><strong aria-hidden="true">7.1.</strong> Discrete event simulation</a></li><li class="chapter-item expanded "><a href="../trafficsim/travel_demand.html"><strong aria-hidden="true">7.2.</strong> Travel demand</a></li><li class="chapter-item expanded "><a href="../trafficsim/gridlock.html"><strong aria-hidden="true">7.3.</strong> Gridlock</a></li><li class="chapter-item expanded "><a href="../trafficsim/trips.html" class="active"><strong aria-hidden="true">7.4.</strong> Multi-modal trips</a></li><li class="chapter-item expanded "><a href="../trafficsim/live_edits.html"><strong aria-hidden="true">7.5.</strong> Live edits</a></li><li class="chapter-item expanded "><a href="../trafficsim/parking.html"><strong aria-hidden="true">7.6.</strong> Parking</a></li><li class="spacer"></li></ol></li><li class="chapter-item expanded "><a href="../project/index.html"><strong aria-hidden="true">8.</strong> Project</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../project/roadmap.html"><strong aria-hidden="true">8.1.</strong> Roadmap</a></li><li class="chapter-item expanded "><a href="../project/motivations.html"><strong aria-hidden="true">8.2.</strong> Motivations</a></li><li class="chapter-item expanded "><a href="../project/history/index.html"><strong aria-hidden="true">8.3.</strong> History</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../project/history/backstory.html"><strong aria-hidden="true">8.3.1.</strong> Backstory</a></li><li class="chapter-item expanded "><a href="../project/history/year1.html"><strong aria-hidden="true">8.3.2.</strong> Year 1</a></li><li class="chapter-item expanded "><a href="../project/history/year2.html"><strong aria-hidden="true">8.3.3.</strong> Year 2</a></li><li class="chapter-item expanded "><a href="../project/history/year3.html"><strong aria-hidden="true">8.3.4.</strong> Year 3</a></li></ol></li><li class="chapter-item expanded "><a href="../project/CHANGELOG.html"><strong aria-hidden="true">8.4.</strong> Full CHANGELOG</a></li><li class="chapter-item expanded "><a href="../project/references.html"><strong aria-hidden="true">8.5.</strong> References</a></li><li class="chapter-item expanded "><a href="../project/collaborations.html"><strong aria-hidden="true">8.6.</strong> Collaborations</a></li></ol></li></ol>
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<h1 class="menu-title">A/B Street</h1>
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<h1><a class="header" href="#multi-modal-trips" id="multi-modal-trips">Multi-modal trips</a></h1>
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<p>A single trip consists of a sequence of <code>TripLegs</code> -- walking, operating a
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vehicle (car or bike), and riding the bus. Depending whether a trip begins or
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ends at a border or building, there are many combinations of these sequences.
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This is a way to categorize them into three groups. I'm not sure it's the
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simplest way to express all the state transitons.</p>
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<h2><a class="header" href="#walking-only-trips" id="walking-only-trips">Walking-only trips</a></h2>
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<p><img src="../mdbook-plantuml-img/bbf8881e880a261530dd998679b4f47108dfc748.svg" alt="" /></p>
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<h2><a class="header" href="#trips-starting-from-a-border" id="trips-starting-from-a-border">Trips starting from a border</a></h2>
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<p><img src="../mdbook-plantuml-img/1cd9d730c8982c5ba59b825b427e712fab82e681.svg" alt="" /></p>
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<h2><a class="header" href="#trips-starting-from-a-building" id="trips-starting-from-a-building">Trips starting from a building</a></h2>
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<p><img src="../mdbook-plantuml-img/92ec1d5cbfccd87df09b67ac1a2b26aebf81eee8.svg" alt="" /></p>
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<h2><a class="header" href="#spawning-code-overview" id="spawning-code-overview">Spawning code overview</a></h2>
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<p>As of November 2020, starting a traffic simulation works like this:</p>
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<ol>
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<li>Something creates a <code>Scenario</code>, which defines a bunch of people. Each person
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has a schedule of trips, carrying them between <code>TripEndpoints</code> via some
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<code>TripMode</code>, leaving at some <code>Time</code>.</li>
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<li>When a scenario is instantiated, every trip for every person passes through
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<code>TripSpec::maybe_new</code>. This transforms the origin, destination, and mode into
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a <code>TripSpec</code>.</li>
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<li><code>TripSpec::to_plan</code> further validates these and attempts to repair impossible
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plans. Each <code>TripSpec</code> is turned into a list of <code>TripLegs</code>. The <code>TripSpec</code> is
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then passed to the discrete-event scheduler inside a <code>Command::StartTrip</code>.
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This way, <code>TripManager</code> knows about all trips immediately, and at the right
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time, each trip can be initiated.</li>
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<li>Later, the scheduler gets one of these commands, and calls
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<code>TripManager::start_trip</code> with the <code>TripSpec</code>. Each type of trip has its own
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initialization logic to kick off the first leg of the trip.</li>
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<li>Most trips have multiple legs. When the first car, bike, or pedestrian
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reaches their goal, <code>TripManager</code> gets called with some sort of transition
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function to initiate the next leg of the trip, or declare the trip finished.
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These transition functions also record stats from that leg of the trip, like
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total blocked time.</li>
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</ol>
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<p>What're the different <code>TripSpec</code> cases, and what <code>TripLegs</code> do they get turned
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into?</p>
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<ul>
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<li><code>VehicleAppearing</code>: Starts at a border. Drive, then maybe walk to the
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destination building.</li>
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<li><code>SpawningFailure</code>: No trip legs; just create and immediately cancel the trip.</li>
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<li><code>UsingParkedCar</code>: Starts at a building. Walk (to the parked car), drive, then
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maybe walk to the destination building (after parking again).</li>
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<li><code>JustWalking</code>: Just walk between two buildings/borders.</li>
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<li><code>UsingBike</code>: Starts at a building. Walk to the nearest bikeable lane, drive,
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then maybe walk to the destination building. (Note that starting a bike from a
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border uses <code>VehicleAppearing</code>.)</li>
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<li><code>UsingTransit</code>: Walk, ride the bus, maybe walk again. No transfers yet; only
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rides one bus between two stops.</li>
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</ul>
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<p><code>TripManager</code> has a whole bunch of transition functions:</p>
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<ul>
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<li><code>car_reached_parking_spot</code>: drive -> walk, unless the destination building is
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where we parked</li>
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<li><code>ped_reached_parking_spot</code>: walk -> drive</li>
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<li><code>ped_ready_to_bike</code>: walk -> bike</li>
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<li><code>bike_reached_end</code>: bike -> walk</li>
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<li><code>ped_reached_building</code>: walk -> done</li>
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<li><code>ped_reached_bus_stop</code>: walk -> wait or ride bus</li>
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<li><code>ped_boarded_bus</code>: waiting -> ride bus</li>
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<li><code>person_left_bus</code>: riding bus -> walk</li>
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<li><code>ped_reached_border</code>: walk -> done</li>
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<li><code>transit_rider_reached_border</code>: ride bus -> done</li>
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<li><code>car_or_bike_reached_border</code>: drive -> done</li>
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</ul>
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<p>There are at least a few use cases motivating the cleanup of all of this
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structure:</p>
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<ul>
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<li>Capping trips through congested areas. Sometimes this just changes the driving
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route, but sometimes it needs to cancel trips, convert driving trips to
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walking/transit, or delay the trip's start.</li>
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<li>Multiple public transit rides in a single trip, aka transferring</li>
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<li>Handling live map edits in the middle of a trip</li>
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