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TransCAD

Networks and Shortest Paths

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Networks and Shortest Paths

A network is a special TransCAD data structure that stores important characteristics of transportation systems and facilities.TransCAD uses geographic files to make maps of transportation systems, and networks to solve transportation problems.Shortest paths are routes over a transportation network that have the lowest generalized cost, where the cost can be any combination of factors such as distance, time, or actual dollar cost of travel.

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Link Costs and Other Attributes

Type of Network

Cost Other Attributes

Streets or Highways

Length, travel time, tolls

Number of lanes, restrictions on trucks or hazardous materials

Pipelines Length, flow rate

Diameter, material

Railroads Length, travel time

Owner of the track, trackage rights, condition

Commercial Airline

Length, ticket price

Carrier, capacity

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Create a Network File (BOS_HWY.MAP)

Has to be a line layer

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Choose the Active Network

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Choose the Active Network from the Network Settings Dialog Box

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Create a Lines of Sight Network

Path will avoid the obstacles

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Shortest Path OverviewThere are three ways to solve a shortest path problem: Using the Shortest Path toolbox to find the

shortest path from a single origin to a single destination, with any number of intermediate points

Solving a multiple shortest path an saving it to a route system

Creating a shortest path matrix that contains the costs of a shortest path between a set of origins and destinations

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Solve a Shortest Path (S_PATH.MAP)

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By clicking on them

Click to activate the Add a Stop by Clicking tool, and then click on the map at each desired stop location.

By typing an address

Click to display the Add Stop Number # dialog box, where # is the number of the next stop. Type the street number and street name or the names of intersecting streets, type the city and state and/or ZIP Code, and click OK.

Based on a point layer

Click to display the Add Stops dialog box. Choose a layer and selection set from the drop-down lists, and click OK.

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When you generate a shortest path, you might also want to compute the total value of other network attributes along that path.

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Solve Multiple Shortest Paths (M_PATH.MAP)

Select the points you want to use as origins

Destinations, or Intermediate points. You may use or other

selecting methods.

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Calculating Point-to-Point Distance (DISTANCE.WRK)

Active a dataview with those columns (distance.wrk)

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Disabling and Enabling Links in a Network

TransCAD allows you to enable or disable selected links in a network file. This can be useful when you want to temporarily modify the links that can be used in finding a path. For example: A drawbridge has been raised and you want to find the

fastest alternate route in an emergency response situation. A road is closed for construction and you want to analyze

traffic flow after the closure to see where congestion will be most severe.

In a planning application, you are considering two or more scenarios. You can include links for all possible scenarios in the network and enable or disable the links from each scenario as desired.

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Disable Links in a Network (LINK.MAP)

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Enable Links in a Network

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To see Which Links are Enabled or Disabled

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Update Link Costs or Other Attributes

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Updating Network Link Attribute Fields

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How One-Way Streets Are Defined

Every line layer contains a special data field( called Direction or DIR) that TransCAD used to keep track of one-way streets.This field contains a zero when a link is two-way. If the link is one-way, this field contains a 1 or a –1, where the sign indicates the allowable direction of flow: 1 – Travel is one-way in the same direction in which the

coordinates of the line feature are stored(topological direction)

-1 – Travel is one-way in the opposite direction from which the coordinates of the line feature are stored( reverse topological direction)

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Display Arrowheads (ONE_WAY.MAP)

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Marking One-Way StreetsMake a selection first