Exercise 12: Performing network analysis using restriction attributes

Complexity: Intermediate Data Requirement: ArcGIS Tutorial Data for Desktop Data Path: C:\ArcGIS\ArcTutor\Network Analyst\Tutorial Goal: Learn how to configure restriction attributes and perform network analyses with them to prohibit, avoid, or prefer network elements.

In this exercise, you will solve a simple route using restriction attributes with different Restriction Usage parameter values to avoid tollways and prefer designated truck routes.

Note:

The data for this exercise and the other exercises in the Network Analyst tutorial is available on ArcGIS.com. After downloading the data, you can extract it wherever you like. It may be helpful, however, to extract it to C:\arcgis\ArcTutor since the tutorial refers to this path as the default location for the data.

Adding Network Analyst controls to ArcMap

Steps:

1. If you have Exercise12.mxd open in ArcMap, skip to step 6.
2. Start ArcMap by clicking Start > All Programs > ArcGIS > ArcMap 10.1.
3. On the ArcMap - Getting Started dialog box, click Existing Maps > Browse for more.

   The Open ArcMap Document dialog box appears.

4. Browse to C:\ArcGIS\ArcTutor\Network Analyst\Tutorial.

   This is the default installation location for the tutorial data.

5. Double-click Exercise12.mxd.

   The map document opens in ArcMap.

6. Enable the ArcGIS Network Analyst extension.
   1. Click Customize > Extensions.

      The Extensions dialog box opens.

   2. Check Network Analyst.
   3. Click Close.

If the Network Analyst toolbar is not displayed, you need to add it.

7. Click Customize > Toolbars > Network Analyst.

   The Network Analyst toolbar is added to ArcMap.

If the Network Analyst window is not displayed, you need to add it.

8. On the Network Analyst toolbar, click the Network Analyst window button .

   You can dock or undock the Network Analyst window.

Examining the Restriction Usage parameter in the network dataset properties

This map displays the road network in the San Diego area. The purple highway in the southeast area of the map represents a tollway. Designated truck routes are displayed with white diamonds along white line features.

The network dataset currently displayed in the map has many restriction attributes that you can use to meet routing preferences and requirements. In this section, you will examine how a restriction attribute is configured and learn about its default parameter, Restriction Usage.

Steps:

1. Click the Catalog button on the Standard toolbar.

   The Catalog window opens.

2. Browse to C:\ArcGIS\ArcTutor\Network Analyst\Tutorial.

   This is the default installation location for the tutorial data.

3. Double-click SanDiego.gdb > Transportation > Streets_ND.

   The Network Dataset Properties dialog box opens.

4. Click the Attributes tab.

   The network's attributes are listed, most of which are restriction attributes. A restriction attribute represents a driving preference or requirement; for instance, Avoid Unpaved Roads lets you avoid any gravel, dirt, or other unpaved roads. Height Restriction makes it possible to route around any clearances that are lower than the height of your vehicle. If you are carrying corrosive materials on your vehicle, using the HazMat: Corrosive Goods Restricted restriction prevents hauling the materials along roads where it is marked as illegal to do so.

   A parameter named Restriction Usage is automatically added when you create a restriction attribute. In the following steps, you will take a closer look at this parameter.

5. Click Add.

   The Add New Attribute dialog box opens.

6. Choose Restriction from the Usage Type drop-down list.

   The Restriction Usage property is enabled.

7. Click the Restriction Usage drop-down list to see the options available.

   This property sets the default value for the Restriction Usage parameter and thus sets the default behavior for the restriction attribute you are creating. The value specifies whether the elements that use the restriction are prohibited, preferred, or avoided; also, it specifies the degree to which they are avoided or preferred.

   Later in this exercise, you will use a restriction attribute to avoid toll roads. The default value for the Restriction Usage parameter of the Avoid Toll Roads restriction is Avoid: Medium. This means that when the restriction is used, the solver will try to route around toll roads when it can. Avoid: Medium also indicates how important it is to avoid toll roads in a network analysis; it has a medium priority. Choosing Avoid: Low would put lower importance on avoiding tolls; choosing Avoid: High instead would give it a higher importance and thus make it more acceptable for the solver to generate longer routes to avoid tolls. Choosing Prohibited would entirely disallow travel on toll roads, making it impossible for a route to traverse any portion of a toll road.

   Keep in mind that avoiding or prohibiting toll roads, and thus avoiding toll payments, is the objective for some; in contrast, others prefer to drive on toll roads because avoiding traffic is more valuable to them than the money spent on tolls. In the latter case, you would choose Prefer: Low, Prefer: Medium, or Prefer: High. The higher the preference, the farther the solver will go out of its way to travel on the elements that use the restriction.

   Due to these kinds of differing perceptions and needs, the ArcGIS Network Analyst extension adds the Restriction Usage parameter to restriction attributes by default. Since it's a parameter, you can choose how the solver should respond to the restrictions before each solve.

8. Click Cancel.

   The Add New Attribute dialog box closes.

You can change the default value of a Restriction Usage parameter at any time. The next steps show how you can do this.

9. Click Avoid Toll Roads.
10. Click Parameters.

    The Avoid Toll Roads Parameters dialog box opens. Notice that the default value is Avoid: Medium. By clicking this value and choosing a different value, the default value would be changed; however, leave this value as it is.

11. Click Cancel.

    The Avoid Toll Roads Parameters dialog box closes.

12. Click Cancel.

    The Network Dataset Properties dialog box closes.

Examining the Restriction Usage parameter in the network analysis layer properties

In this section, you will take a quick tour of where you can view and change the restriction attribute settings of a network analysis layer.

Steps:

1. Click Network Analyst on the Network Analyst toolbar and click New Route.

   A route analysis layer is added to the document in the Network Analyst and Table Of Contents windows.

2. Click the Analysis Layer Properties button on the Network Analyst window.

   The Layer Properties dialog box opens.

3. Click the Analysis Settings tab.

   The Restrictions frame on the tab lists all the available restrictions. Since this network analysis layer was created on the same network dataset that you were examining in the last section, the same restriction attributes are listed here. Note that Avoid Toll Roads is unchecked, since it isn't used by default.

4. Click the Attribute Parameters tab.

   All the network attributes that have parameters are listed here. Since restriction attributes have a Restriction Usage parameter by default, they are all listed here.

   You can choose different parameter values for the current analysis layer under the Value column.

5. Click Cancel.

   The Layer Properties dialog box closes.

Solving a route analysis

In this section, you will load stops into the analysis and solve using the default analysis settings.

Steps:

1. In the Network Analyst window, right-click Stops (0) and choose Load Locations.

   The Load Locations dialog box opens.

2. Choose Stops from the Load From drop-down list.
3. Click OK.

   Five stops are loaded. You can see them in the map display and in the Network Analyst window.

4. Click the Solve button on the Network Analyst toolbar.

   The best route following the predefined sequence is shown on the map. Notice that the third stop is on the toll road, and because of that, the route travels along the toll road.

Prohibiting toll roads

Next, you will solve the same route analysis, but indicate that you want the route to prohibit travel along toll roads.

Steps:

1. Click the Analysis Layer Properties button on the Network Analyst window.

   The Layer Properties dialog box opens.

2. Click the Analysis Settings tab.
3. In the Restrictions frame, check Avoid Toll Roads.
4. Click the Attribute Parameters tab.
5. Find Avoid Toll Roads and change its value from Avoid: Medium to Prohibited.
6. Click OK.
7. Click the Solve button on the Network Analyst toolbar.

   The Network Analyst Messages dialog box appears and warns you the stop on the toll road couldn't be reached.

   This is a drawback of prohibiting network elements entirely; the network locations that are on those elements can't be reached. As you'll see in the next section, choosing to avoid toll roads, rather than to prohibit them entirely, will make it possible to stay off restricted elements for the most part but reach network locations that are on those elements.

8. Click Close.

   The Network Analyst Messages dialog box closes.

   The map shows that the route circumvents the toll road entirely, and thus it doesn't visit the third stop.

Avoiding toll roads

Next, you will solve the same route analysis, but indicate that you want the route to merely avoid toll roads.

Steps:

1. Click the Analysis Layer Properties button on the Network Analyst window.

   The Layer Properties dialog box opens.

2. Click the Attribute Parameters tab.
3. Find Avoid Toll Roads and change its value from Prohibited to Avoid: Medium.
4. Click OK.
5. Click the Solve button on the Network Analyst toolbar.

   The Network Analyst Messages dialog box appears to warn that a stop is located on a road that uses a restriction and, even though you chose to avoid toll roads, the resultant route still traverses one.

6. Click Close.

   The Network Analyst Messages dialog box closes.

   The map shows that the route avoids the southern portion of the toll road but travels on it to reach stop 3, then stop 4. The route could have traveled less on the toll road between stops 3 and 4, but Network Analyst determined that the detour would be too long given the Restriction Usage parameter value of Avoid: Medium.

   In the next set of steps, you will make avoiding toll roads a higher priority and see the results.

7. Click the Analysis Layer Properties button on the Network Analyst window.
8. Click the Attribute Parameters tab.
9. Find Avoid Toll Roads and change its value to Avoid: High.
10. Click OK.
11. Click the Solve button on the Network Analyst toolbar.

    The Network Analyst Messages dialog box appears again with the same warnings as the last time.

12. Click Close.

    The Network Analyst Messages dialog box closes.

    You can see on the map that the route enters the tollway to reach stop 3 and exits the tollway immediately afterwards.

    Tip:

    To quickly compare the results of two consecutive solve operations, click the Undo button , then the Redo button .

In this section, you've seen that routes don't traverse roads that use prohibit-restrictions, even if a stop is located on such a road. By choosing avoid-restrictions instead, the stop can be reached, and Network Analyst tries to bypass the restricted roads according to whether you set the restriction's parameter to Avoid: Low, Avoid: Medium, or Avoid: High.

Preferring designated truck routes

In this section of the exercise, you will continue to use the same route analysis layer and avoid toll roads; however, this time you will find the best route for a truck instead of an automobile. You will use a restriction attribute so that designated truck routes are preferred.

Steps:

1. Click the Analysis Layer Properties button on the Network Analyst window.

   The Layer Properties dialog box opens.

2. Click the Analysis Settings tab.
3. In the Restrictions frame, uncheck Driving an Automobile.
4. Check Driving a Truck.

   This restriction attribute represents roads that are prohibited to truck traffic. Its default Restriction Usage parameter value is Prohibited. You won't change this parameter value.

5. Check National STAA Preferred Route.

   This restriction attribute represents roads that are federally designated as truck routes. This designation is given to roads that are conducive to truck driving and include minimum standards for clearances and weight limits. Truck drivers can mitigate many potential problems simply by following designated truck routes as much as possible.

   Roads with this designation are symbolized on the map with white lines and diamond hash marks.

   Be careful not to confuse this restriction attribute with the National STAA and Locally Preferred Routes attribute. The latter restriction attribute includes roads that may not conform to federal standards.

6. Click the Attribute Parameters tab.
7. Find National STAA Preferred Route and note that its default value is Prefer: Medium.
8. Click OK.
9. Click the Solve button on the Network Analyst toolbar.
   The route remains the same. Much of the route was already traveling along the national STAA roads.
10. Click the Analysis Layer Properties button on the Network Analyst window.

    The Layer Properties dialog box opens.

11. Click the Attribute Parameters tab.
12. Find National STAA Preferred Route and change its value to Prefer: High.
13. Click OK.
14. Click the Solve button on the Network Analyst toolbar.

    The overall route is longer now, but the amount of time spent driving on roads that aren't designated as national STAA roads is less.

You have seen in this exercise that restriction attributes allow you to model travel preferences and requirements. Solving an analysis using different restriction attributes and Restriction Usage parameter values can affect the results.

This exercise demonstrated restriction capabilities using a route analysis layer for simplicity; however, these same capabilities are available with other network analysis layers as well.