Network Structure

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Overview

A SwashSim network is composed of the following components:


 * Nodes (entry, connector, exit)
 * Entry
 * Vehicles enter the network at entry nodes
 * Id numbering: Entry node numbering starts at 701 and increments by 1 with each successive entry node added to the network
 * Exit
 * Vehicles exit the network at entry nodes
 * Id numbering: Exit node numbering starts at 801 and increments by 1 with each successive exit node added to the network
 * Ramp connector
 * Used to identify a link as an on- or off-ramp connecting to a freeway mainline segment
 * Id numbering: Ramp connector node numbering starts at 601 and increments by 1 with each successive ramp connector node added to the network
 * Connector
 * Connector nodes are used in all other link connection circumstances


 * Links (entry, connector, exit)
 * Each link is bounded by an upstream node and downstream node
 * Id numbering: Concatenation of upstream and downstream node Id's, in direction of travel
 * Orientation angle
 * Lanes
 * Id numbering
 * From outside to inside (lane 1 is outer most lane)
 * Types
 * Regular
 * Left Turn Bay
 * Etc.
 * Up/downstream connecting link/lane Id's


 * Control Points
 * Detectors

Network Properties Absolute coordinate values are irrelevant; only relative node coordinate values are important.
 * x, y coordinates

Node Properties

X/Y Coordinates Each coordinate has an X and Y position. The units are feet. However, the absolute coordinate values are irrelevant--only the relative coordinate positions between nodes are relevant to the internal SwashSim calculations. In the Freeway and Two-Lane Highway modules, these coordinate values are automatically created (as a function of link length, orientation, and curvature). In the Custom network creation module, these coordinate values must be explicitly specified.

Common Link Properties

Upstream/Downstream Node ID A link has a beginning (upstream) and ending (downstream) node. Link ID values are created by concatenating the upstream and downstream node ID values. For example, Link ID ‘12’ corresponds to a link that has upstream node ID ‘1’ and downstream node ID ‘2’. The upstream and downstream node IDs are set automatically in the various network creation user interface (UI) screens. However, those values can be overridden by the user in the 'Custom' network creation module.

Length For tangent segments, the link length is entered in this cell. For curved links, the link length will be based on the curve radius and central angle. Consequently, the length cell for a curved link will be colored gray, indicating that it cannot be edited directly. User input of length is restricted to integer values; however, the program may replace entered values with decimal values as a consequence of curved links and/or coordinate point adjustments.

Orientation Angle This input corresponds to a compass angle based on the direction of travel (see Figure below). For example, the segment angle would be set as follows for the given travel directions: In the Freeway and Two-Lane Highway modules, the orientation angle only needs to be specified for the first link. Subsequent link orientation angles are calculated by the program and are a function of the previous link orientation angle and any specified horizontal curvature. In the Custom network creation module, the orientation angle is calculated by the program, based on the entered node coordinate positions.
 * 0o for perfectly horizontal east-to-west travel
 * 180o for perfectly horizontal west-to-east travel
 * 90o for perfectly vertical south-to- north travel
 * 270o for perfectly vertical north-to-south travel.

Horizontal Curvature A link can either be straight (i.e., tangent) or curved. If it is a curved link,

If a link is specified to be a curve, additional inputs are required, specifically:

Control Point X/Y Coordinates

control point (a point in between the link start and end points that affect the amount of curvature of the link) coordinates need to be specified as well as the turning direction.

Turning Direction

Curve Radius

Central Angle curve direction (this latter input corresponding to the general turning direction of the curve). Filling in the central angle and radius of the curve will automatically adjust the segment length and control points accordingly.

Curve Radius

Grade The percent incline or decline of the segment. This is measured as the elevation change over the length of the segment divided by the segment length, multiplied by 100.

Free-Flow Speed For tangent links, the free-flow speed must be explicitly specified. For curved links, the free-flow speed can be explicitly specified or it can be estimated. In the latter case, the free-flow speed is estimated according to the model discussed in Appendix X. Units of entry are ft/s.

Upstream/downstream connecting link ID's
 * An example of how to specify this coding can be found here.
 * Lane data, as outlined below
 * Note that the length and orientation angle (link to graphic) of the link is calculated from the node positions.

Upstream/downstream connecting lane ID's

Freeway-only Link Properties

Two-lane highway-only Link Properties

Passing in Oncoming Lane The options for passing in the oncoming lane are:
 * Allowed ‘Direction 1’
 * Allowed ‘Direction 2’
 * Allowed Both Directions
 * Not Allowed

Passing/Climbing Lane Direction The options for passing/climbing lane direction are:
 * None
 * Direction 1
 * Direction 2
 * Both Directions

Passing/Climbing Lane Rule If a passing/climbing lane has been specified, one of the following driving rules can be specified:
 * Slow Vehicles Move Over
 * Fast Vehicles Move Over



Connecting Link IDs

Connecting Lane IDs