Technicalities about "%"?

Usage of "%"

I'm almost positive it's a prepositional phrase since it's really means "per cent" or "per 100".

So in a sentence like:

90% of my street are doing lawn work.

It would be "are" and not "is" because both "%" and "of my street" are prepositional phrases and therefore cannot contain the subject.

Am I right?

Like a lot of, something like 90% of functions not so much as a preposition as it does a premodifier. And premodifiers work like adjectives. They do not change the head noun, which remains the grammatical subject and still must be agree with the verb in number.

• People are coming.
  Trouble is avoided.
• A lot of people are coming.
  A lot of trouble is avoided.
• Ninety percent of the people are coming.
  Ninety percent of the trouble is avoided.
• One percent of the people are coming.
  One percent of the trouble is avoided.

As you see, you can remove the leading a lot of or the X% of, and nothing changes. Like adjectives, these premodifiers do not change the grammatical subject or influence the verb. The head noun does not change.

Grammar Girl says that it depends on the object of the preposition.

About 90% of my neighbors are doing lawn work. (plural)

About 90% of the population has filed their taxes. (singular)

(Incidentally, several sources think it's better start a sentence with something other than a numeral; this is why I started the examples with "About.")