Speed settings are used to calculate quickest routes. Each road segment in a road map should have a maximum permitted speed value or segments should be classified by type, such as highway, major road, urban street, etc. If there are no classes or speed values, calculations will assume the same speed settings for all road segments in the road map.
There are two ways to set speed values for road segments:
1. The road map may have a field that stores speed values for each road segment.
The sample roads.shp shapefile has the SPEED field, which contains pre-calculated speed values for each road segment in miles per hour. Therefore, we simply need to select this field in the 'Speed field' combo-box:
2. The road map may have a field that stores the road class or type of each road segment.
For example, road maps that are available from the US Census have a Feature Classification Code for each road segment. These codes are contained in the FCC field. The Road Network Builder utility associates these road codes with speed values. This is done in the 'Road class field' combo-box, which looks like this:
Select the FCC field and enter the road codes and their associated speed values in the table.
You can also save the entered values in a file for later use. Click the 'Save road classes...' button, enter a name for the file in the dialog box and click the 'Save' button:
Use the 'Load road classes...' button to load these saved road classes whenever you need them.
Click here to go to Step 3
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