Available with Network Analyst license.
You can perform a network analysis that uses a parameterized attribute while computing the solution.
The first step to performing a network analysis using a parameterized attribute is to have a network dataset with a parameterized attribute.
What are parameterized attributes?
A parameterized attribute is a type of attribute that includes in its evaluation a parameter that you can change at solve time.
The value of a parameter can be altered to make the parameterized attribute change the way it functions. For example, you can enter a scale factor on a parameterized drive-time attribute to increase travel times for a given solve operation. You can specify the height of a vehicle on a parameterized restriction attribute so that routes don't traverse edges that have a maximum height value that is less than the vehicle's height.
The Restriction Usage parameter
By default, all restriction attributes are assigned a parameter: Restriction Usage. You choose a value for this parameter to prefer, avoid, or entirely prohibit network elements that use the restriction; furthermore, you specify the degree to which elements are avoided or preferred.
Most often, this attribute is set to Prohibit. Certainly, you would choose Prohibit for restrictions based on physical limits, like height limits. However, you can choose to merely avoid or even prefer network elements by choosing other values; for example, you might avoid toll roads or prefer designated truck routes when routing trucks.
Setting the restriction usage parameter for a restriction attribute to Avoid Low/Medium/High makes it a soft restriction, because it means that the restricted road segments can still be traversed, as opposed to selecting Prohibited, which makes it a hard restriction. When choosing to use soft restrictions internally the solver will adjust the impedance cost for the roads with soft restrictions and use the adjusted impedance cost when finding paths. This will penalize the roads with the soft restrictions present encouraging the solver to look for alternative paths. Soft restricted roads can still be taken by the route if it results in a smaller adjusted impedance cost. The soft restrictions only adjust the impedance cost internally during the path finding process. When reporting the impedance at the end of the solve, it will be the true impedance costs.
For the OD Cost Matrix Solver and the Closest Facility Solver, they use the soft restricted adjusted impedance values for determining the optimal path between incidents and facilities. In the above stylized network, when going from incident B to facility 2, the solver would choose the path that uses the soft restricted edge because the adjusted impedance cost is only 14, whereas the detour option that does not use the soft restricted edge would have an adjusted impedance cost of 16 (same as the true impedance cost since it does not have any edges that have soft restrictions).
Two aspects to consider when using both soft restrictions and cutoff values for either the OD Cost Matrix Solver or the Closest Facility Solver is how the ranking is reported and the possibility of not finding all expected candidates. When ranking the routes for OD Cost Matrix Solver and Closest Facility Solver the true impedance costs are used instead of the soft restricted adjusted impedance cost. Using that same stylized example above, the route to facility 2 would be ranked as 1 while the route to facility 1 would be ranked as 2. This is because the true impedance costs to facility 2 is only 9 even though the adjusted impedance cost used to find that path is 14. The true impedance cost and the adjusted impedance cost to facility 1 is 10.
In rare occasions, no path will be found between origin/destination or facility/incident when using both soft restrictions and cutoff values. This is because the most optimal path from the starting to ending locations is found using the soft restricted adjusted impedance costs. If there are two route options between the two locations and the one with the smaller adjusted impedance cost is the longer route which detours around a soft restriction, it will be recorded as the optimal path to that location. However, if the cutoff value is placed strategically between the true impedance costs of those two route options, then even though it is still feasible to get to the location within the cutoff value, no route will be returned because the optimal adjusted path found has a true impedance cost that is above the cutoff value.
In the above stylized example, going from Origin A to Destination 1, there are two main options. The red route takes a toll road and has a true impedance cost of 9. The blue route does not take any toll roads and has a true impedance cost of 14. When the avoid toll roads parameter is set to avoid medium the soft restricted adjusted impedance cost of the toll road option (adjusted cost of 16) becomes bigger than the detour (adjusted cost of 14). The detour path option is, therefore, considered the optimal path between these two locations. If the cutoff value is set to 10, then the solver will not return a solution because it is below the true impedance cost of the optimal path. If you encounter such a situation and believe there is a route below the cutoff value, try removing the soft restrictions and resolving to find the shortest true impedance cost path. If, alternatively, you still want to use the soft restrictions to avoid certain roads but believe that a path should be found between the two locations, then try either increasing the cutoff value or not using cutoffs.
Performing a network analysis in ArcMap using a parameterized attribute
You can apply the following workflow to use parameterized attributes in any network analysis. First, ensure that you have an analysis layer and all required network analysis objects before carrying out these steps.
On the Table Of Contents window, double-click the network analysis layer to view its properties.
Click the Analysis Settings tab.
Set the parameterized attributes to be used in the analysis. To use a parameterized cost attribute, choose it for the Impedance setting. To use parameterized restriction attributes, check them in the Restrictions section.
For example, you could change Impedance to read a parameterized scaled cost attribute and check Height, Hazmats Prohibited, and Hazmats Preferred restrictions.
Click the Attribute Parameters tab.
If you need to adjust any of the parameter values for the attributes, click in the Values column for the row with the right attribute-parameter combination and update the parameter value.
For example, the following changes could be made to an analysis, assuming the network dataset has the appropriate attributes and parameters:
Set the Drive Time Factor parameter of the DriveTime_Scaled cost attribute to 1.5 to increase travel times by 50 percent to account for icy roads.
Set the Vehicle Height parameter of the Height attribute to 13.5 feet to represent the height of the vehicle for which you are currently solving an analysis.
Set the Restriction Usage parameter of the same Height attribute to Prohibited since you would never want your vehicle to try to drive under a bridge with a minimum clearance that is lower than the height of your vehicle.
Set the Restriction Usage parameter of the Hazmats Prohibited attribute to Prohibited to never allow the vehicle for which you're solving to go on roads that are posted as prohibited to hazmat vehicles.
If detouring around roads that are off limits to hazmat vehicles isn't an option—for instance, a stop the truck must visit is on such a road—you can relax the constraint by changing the Restriction Usage parameter value from Prohibit to Avoid: High. This causes the solver to try to stay off the restricted roads; it travels on them only if detouring around the roads is too costly or if a restricted road must be traversed to reach a stop.
Set the Restriction Usage parameter of the Hazmats Preferred attribute to Prefer: Low, Prefer: Medium, or Prefer: High. The choice of low, medium, or high depends on whether it is slightly, somewhat, or very important that your truck stays on designated hazmat roads as much as possible.
Click OK to save these settings.
On the Network Analyst toolbar, click the Solve button to generate results that use these parameterized attributes.