I'm learning how to use the Location-Allocation feature in the Network Analysis to determine possible locations for future fire stations. Is there anyway to add proposed streets to the analysis? We have several main through streets that will be built within the next two years and need to be factored into the analysis.
Yes, essentially you could digitize new street features into the source street feature class. The only typical "gotcha" is to make sure that you're aware of the network dataset's connectivity rules to ensure that traffic can flow from existing streets to your hypothetical/future streets: http://desktop.arcgis.com/en/arcmap/latest/extensions/network-analyst/understanding-connectivity.htm
You might want to make a copy of the network dataset and use the copy for your future modeling.