Filters are used in the Scenario definition (see above), and allow the budget to be applied to only a subset of the roads (this is useful to apply budgets selectively to the sealed and unsealed networks, for example). 

Add and remove Scenario Filters with the buttons provided: .  If a Scenario Filter is being used by a scenario, deletion will be disallowed.  First deselect it in the Scenario.

When adding a Scenario Filter, the following screen appears.  The most usual filters will involve surfaces.  In the example below, a filter has been set up to contain descendants of the Rural Sealed Surface Types.

By adding lines, a comprehensive filter can be established.  E.g. adding the Township Sealed Surface Types will provide a filter of all sealed types.  The example below demonstrates this, along with a test list of the surfaces.