uxsim.Link¶

class uxsim.Link(W, name, start_node, end_node, length, free_flow_speed=20, jam_density=0.2, jam_density_per_lane=None, number_of_lanes=1, merge_priority=1, signal_group=[0], capacity_out=None, capacity_in=None, eular_dx=None, attribute=None, user_attribute=None, user_function=None, auto_rename=False)[source]¶

Link in a network.

Create a link

Parameters:

W (object) – The world to which the link belongs.
name (str) – The name of the link.
start_node (str | Node) – The name of the start node of the link.
end_node (str | Node) – The name of the end node of the link.
length (float) – The length of the link.
free_flow_speed (float, optional) – The free flow speed on the link, default is 20.
jam_density (float, optional) – The jam density on the link, default is 0.2. If jam_density_per_lane is specified, this value is ignored.
jam_density_per_lane (float, optional) – The jam density per lane on the link. If specified, it overrides the jam_density value.
number_of_lanes (int, optional) – The number of lanes on the link, default is 1.
merge_priority (float, optional) – The priority of the link when merging at the downstream node, default is 1.
signal_group (int or list, optional) – The signal group(s) to which the link belongs, default is 0. If signal_group is int, say 0, it becomes green if end_node.signal_phase is 0. If signal_group is list, say [0,1], it becomes green if the end_node.signal_phase is 0 or 1.
capacity_out (float, optional) – The capacity out of the link, default is calculated based on other parameters.
capacity_in (float, optional) – The capacity into the link, default is calculated based on other parameters.
eular_dx (float, optional) – The space aggregation size for link traffic state computation, default is 1/10 of link length or free flow distance per simulation step, whichever is larger.
attribute (any, optional) – Additional (meta) attributes defined by users.
user_attribute (any, optional) – Additional (meta) attributes defined by users. Same functionality to attribute, but with more understandable name.
user_function (func, optinal) – User-defined custom function that is automatically called when timestep is incremented (more precisely, when update() is called). It takes only one argument: the Link object itself. Example: The following code prints the current number of vehicles on the link at each timestep. If user_function=None (default), no functions will be executed. >>> def user_function(link): >>> print(len(link.vehicles)) >>> W = World(…) >>> W.addLink(“link”, “node1”, “node2, 1000, user_function=user_function) >>> … #define your scenario >>> W.exec_simulation()
auto_rename (bool, optional) – Whether to automatically rename the link if the name is already used. Default is False (raise an exception).

speed¶

Average speed of traffic on the link.

Type:: float

density¶

Density of traffic on the link.

Type:: float

flow¶

Flow of traffic on the link.

Type:: float

num_vehicles¶

Number of vehicles on the link.

Type:: float

num_vehicles_queue¶

Number of slow vehicles (due to congestion) on the link.

Type:: float

free_flow_speed¶

Free flow speed of the link.

Type:: float

jam_density¶

Jam density of the link.

Type:: float

capacity_out¶

Capacity for outflow from the link.

Type:: float

capacity_in¶

Capacity for inflow to the link.

Type:: float

merge_priority¶

The priority of the link when merging at the downstream node.

Type:: float

Notes

Traffic Flow Model:

The link model follows a multi-lane, single-pipe approach where FIFO is guaranteed per link and no lane changing occurs.
Fundamental diagram parameters such as free_flow_speed, jam_density (or jam_density_per_lane), and number_of_lanes determine the link’s flow characteristics. Reaction time of drivers REACTION_TIME is a grobal parameter.
Real-time link status for external reference is maintained with attributes speed, density, flow, num_vehicles, and num_vehicles_queue.

Traffic Flow Model Parameters:

Their definition is illustrated as https://toruseo.jp/UXsim/docs/_images/fundamental_diagram.png
If you are not familiar to the traffic flow theory, it is recommended that you adjust only free_flow_speed and number_of_lanes for the traffic flow model parameters, leaving the other parameters at their default values.

Capacity and Bottlenecks:

The capacity_out and capacity_in parameters set the outflow and inflow capacities of the link. If not provided, the capacities are unlimited.
These capacities can represent bottlenecks at the beginning or end of the link.

Connection to Node Model:

At the downstream end of a sending link, vehicles in all lanes have the right to be sent out, but FIFO order is maintained.
At the upstream end of a receiving link, all lanes can accept vehicles.

Parameter Adjustments:

Some traffic flow model parameters like free_flow_speed, jam_density, capacity_out, capacity_in, and merge_priority can be altered during simulation to reflect changing conditions.

Details on Multi-lane model:

Link model:
- Multiple lanes with single-pipe model. FIFO is guaranteed per link. No lane changing.
- Links have a lanes attribute representing the number of lanes.
- Each vehicle has a lane attribute.
- Each vehicle follows the leader vehicle in the same lane, i.e., the vehicle lanes steps ahead on the link.
Node model:
- Sending links:
  
  Vehicles in all lanes at the downstream end of the link have the right to be sent out.
  
  However, to ensure link FIFO, vehicles are tried to be sent out in the order they entered the link. If a vehicle cannot be accepted, the outflow from that link stops.
- Receiving links:
  
  All lanes at the upstream end of the link can accept vehicles.

Details on Fundamental diagram parameters (+: input, ++: alternative input):

free_flow_speed (m/s)+
jam_density (veh/m/LINK)+
jam_density_per_lane (veh/m/lane)++
lanes, number_of_lane (lane)+
tau: y-intercept of link FD (s/veh*LINK)
REACTION_TIME, World.reaction_time (s/veh*lane)
w (m/s)
capacity (veh/s/LINK)
capacity_per_lane (veh/s/lane)
delta: minimum spacing (m/veh*LINK)
delta_per_lane: minimum spacing in lane (m/veh*lane)
q_star: capacity (veh/s/LINK)
k_star: critical density (veh/s/LINK)
capacity_in, capacity_out: bottleneck capacity at beginning/end of link (veh/s/LINK)+
Node.flow_capacity: node flow capacity (veh/s/LINK-LIKE)+

__init__(W, name, start_node, end_node, length, free_flow_speed=20, jam_density=0.2, jam_density_per_lane=None, number_of_lanes=1, merge_priority=1, signal_group=[0], capacity_out=None, capacity_in=None, eular_dx=None, attribute=None, user_attribute=None, user_function=None, auto_rename=False)[source]¶