While someone who owns a hybrid or electric probably should pay a fee, to me it should be dependent on how many miles you drive, not a flat fee.
The average vehicle in America gets 26 miles to gallon. Hybrids average about 35.
Average American drives 14,500 miles. So if 26 miles to a gallon, that's 557 gallons a year
A 100 fee breaks out like this.(Non hybrid).
18.4 cents per gallon tax, (fed) equates to close to 550 gallons a year.
While hybrids average around 420 gallons used. So they are already paying 75 dollars into the highway fund.
So that's seems to me, a penalty, and not a serious effort to make it fair.