Hello Chris. The fields in your barriers should take the form Attr_[Impedance attribute name]. So if your network has an impedance attribute called "TravelTime", and you are using TravelTime as the impedance attribute for the particular analysis where you will be using the barriers, the correct field would be Attr_TravelTime.
Impedance attributes are a property of your network dataset. If you're building your own network dataset, you can give them any names you want. Consequently, there is no set list of possible field names for barriers. The valid values depend on how you've constructed your network dataset.
When you create a network analysis layer (like a Route or Service Area layer), the barriers sublayers should already have the appropriate fields in them, so you don't actually have to construct the fields yourself in advance.
Just in case it's not totally clear, barriers are NOT part of the network dataset. They are part of the network analysis layer and specific to each analysis.
