When something is compared to a subgroup to which it belongs, is usual should be used.
1. He is nicer than usual
2. He is faster than is usual for any human being.
3. Ram is faster than usual today.
4. Emails are often written in a much formal way than is usual in writing.
5. The sun looks less brightly than usual to-day.
6. The new sports car is heavier than is usual for a performance automobile, but it is exceptional because of its high-powered engine .
7. Successful completion of Grammar course is not easy and requires more planning and preparation than is usual for normal course completion .
8. There was a higher ratio of comedy to drama than is usual in a one hour show.
9. I checked this article more carefully than usual for grammatical errors.
10. The gravel was damper than usual, since it rained heavily yesterday.
11. Today I was busier than usual at work.
GMAT Question example:
The Parthenon is larger than usual for a Doric temple, with eight columns on the short sides and seventeen on the long ones rather than the typical six and thirteen.
(B) is usual
(C) has been usual
(D) one usually is
(E) it is usual