Can I rent an intermediate size car if economy size is too small?

Yes.

University policy permits renting up to an intermediate size car. If a bigger vehicle can be reserved for the same price or you receive a free upgrade, provide that explanation in your reimbursement request.

If circumstances require a larger vehicle, please provide the business purpose. For example: I rented a full size car to accommodate seating and luggage for myself and three colleagues, Professor Jones, Professor Lee, and Director Smith.