75 lines
3.6 KiB
ReStructuredText
75 lines
3.6 KiB
ReStructuredText
Routes and Trip Segments
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========================
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In MetroSim, when an agent is traveling from an origin to a destination (optionally, with intermediate stops), he / she chooses between multiple routes to perform his / her trip.
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A route describes the modes of transportation taken to travel from an origin to a destination.
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Hence, in MetroSim, route choice is similar to mode choice.
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More formally, a route is a combination of multiple trip segments, where each trip segment represents only one mode of transportation, allowing for inter-modal trips.
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Routes can range from very simple (e.g., travel by car from O to D) to very complex (e.g., travel by car from O to I\ :sub:`1`, then take metro line 1 from I\ :sub:`1` to I\ :sub:`2`, then walk from I\ :sub:`2` to I\ :sub:`3`, then take bus line 5 from I\ :sub:`3` to D).
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The figure below represents an example of route, with 2 segments.
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The second segment is a public-transit segment containing 3 legs.
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.. math::
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\overbrace{
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\mathbf{O}
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\overbrace{\longrightarrow \text{Car} \longrightarrow}^{\text{segment 1}}
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\mathbf{I_1}
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\overbrace{
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\underbrace{\longrightarrow \text{Metro (line 1)} \longrightarrow}_{\text{leg 1}}
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\mathbf{I_2}
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\underbrace{\longrightarrow \text{Walk} \longrightarrow}_{\text{leg 2}}
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\mathbf{I_3}
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\underbrace{\longrightarrow \text{Bus (line 5)} \longrightarrow}_{\text{leg 3}}
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}^{\text{segment 2}}
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\mathbf{D}
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}^{\text{route}}
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Trip Segments
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-------------
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MetroSim has three different types of trip segments.
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Car segment
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It represents a trip by car from a source node to a target node.
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A car segment is only defined by its source and its target, i.e., there is no intermediate stop and the exact path taken is not determined a priori.
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Public-transit segment
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It represents a public-transit trip from an access stop to an egress stop.
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A public-transit segment is defined by its access stop and its egress stop but also by the sequence of legs taken between the two stops, i.e., there can exist multiple public-transit segments between any two stops.
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A public-transit segment can include walking legs to transfer from one line to another but it always starts and ends with a public-transit leg.
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An example of public-transit segment is: take bus line 1 from stop A to stop B, then walk from stop B to stop C, then take metro line 3 from stop C to stop D.
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Walking segment
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It represents a walking trip from a source node to a target node.
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Trip segments can be classified in three categories, according to the characteristics of the travel utility they imply.
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"Constant" trip segment
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Travel utility is time-invariant (e.g., walking segment).
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"Continuous" trip segment
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Travel utility is continuously time-dependent (e.g., car segment).
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"Discrete" trip segment
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Travel utility is discontinuously time-dependent (e.g., public-transit segment).
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Route Type
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----------
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The route type depends on the type of its segments, according to the following rules:
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- If at least one segment is discrete, then the route is *discrete*.
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- If at least one segment is continuous but no segment is discrete, then the route is *continuous*.
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- If all segments are constant, then the route is *constant*.
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The route type is relevant when computing the expected utility of a route.
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For discrete routes, the utility of all possible departure times is computed (at least partially).
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For continuous routes, the utility is computed for a finite set of departure times.
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For constant routes, the utility is computed only once.
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See :doc:`/architecture/simulator/pre-day_model` for additional details.
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