Conveyance allowance exemption may prevent tax deduction at source if certified and substantiated by the employee. Where conveyance allowance reimburses expenses wholly, necessarily and exclusively incurred for official duties, the disbursing authority may treat it as exempt special allowance for TDS purposes, provided a certificate is endorsed on tax deduction bills and the employee can substantiate the reimbursement before the assessing officer; the authority's satisfaction remains subject to scrutiny and documentation is required to support non-deduction and related adjustments to the standard deduction for TDS computation.