Fixed charges and special assessment included in the property tax deductible?

They are deductible as long as they provide a general community benefit and not a special benefit for your property.

The general principle is that property taxes are deductible if they are ad valorem, based on the value of the property, and assessed uniformly on all similarly situated properties in the community.  However, there is another principle that property taxes are deductible as long as they provide a general community benefit and not a specific benefit.  So a charge for paramedics, for example, that provides a community benefit, is deductible while a charge for streetlights -- when your street has them but other streets don't -- is a benefit to your property and is not deductible.  Another example would be a charge for rebuilding the sewer on your street that is divided up among the properties on your street and added to the property tax bill over a certain number of years.

This is actually a matter of some controversy between the IRS and the state of California.  California has a whole series of "Mello-Roos" taxes that pay for specific services (so communities can get around the state's general property tax cap.)  California has determined that because these taxes are not ad valorem, they are not deductible. But the IRS has ruled that as long as the taxes pay for general community benefits, they are deductible even if they are not ad valorem.  California has agreed go along with the IRS even though they disagree on principle.

See this IRS memo.  https://www.irs.gov/pub/irs-wd/12-0018.pdf

So you need to determine which of the taxes pay for a general community benefit, and which taxes pay for a benefit that is more restricted to your street, house or neighborhood.

"Revenue Ruling 80-121, 1980-1 C.B. 43, notes that a characteristic common to many real property taxes is that the tax is measured by the value of the real property. However, there is no statutory or regulatory requirement that a real property tax be an ad valorem tax to be deductible for federal income tax purposes. Assessments on real property owners, based other than on the assessed value of the property, may be deductible if they are levied for the general public welfare by a proper taxing authority at a like rate on owners of all properties in the taxing authority’s jurisdiction, and if the assessments are not for local benefits (unless for maintenance or interest charges)."