Vouchers cannot be extended. Assuming the OP meant ticketless travel funds, after expiration they can be reissued as a voucher for a fee of $100. This must be requested within 6 months of expiration, and will be usable by anyone for a period of 6 months after issue. Requests are granted on a case-by-case basis, and everything, including the fee amount, is subject to change at any time.