Conveyance allowance treatment: cap on standard deduction where allowance or employer vehicle benefits amount to private conveyance use. Restriction of the standard deduction applies where an employee receives a conveyance allowance or has use of employer motor vehicles otherwise than wholly and exclusively for duties; the substance of a payment controls its treatment so that allowances that in reality are conveyance allowances are subject to the deduction cap regardless of nomenclature, while genuine reimbursement of actual expenses incurred in performance of duties is not subject to that cap, and travel between residence and office is treated as private use.