62 B. Purchase of ticket 7. Unless there is specific advance authorization by OHCHR to the traveller indicating that he or she may make other arrangements, including tickets with low-cost airlines, all tickets shall be purchased by the United Nations in advance of the actual travel, and issued through the travel partner of the United Nations, CWT. Experts who choose to purchase their tickets without prior authorization may not be fully reimbursed as the reimbursement will cover only the amount originally authorized by the United Nations. Reimbursement may also take some time to be completed and will take place only if the original receipt of the ticket purchase is provided. C. Standard of accommodation 8. When a traveller requests a class of ticket (standard of accommodation) different from his/her entitlement or travel authorization, for reasons of personal preference or convenience, or by a route or mode of transportation other than that approved by the United Nations, the traveller is required to pay any additional cost incurred. Such costs are not reimbursable. It should be noted that, should a lower standard of accommodation be selected, the entitlement will be recalculated for that lower fare class. 1. By air 9. The standard of accommodation for experts is the class immediately below first class—i.e., business class—when available. In cases where business class is not available, economy class will be approved. The maximum travel expenses shall be calculated on the basis of the most economical airfare by a direct route at the appropriate standard and rate. The Organization shall assume responsibility for any surcharge that may be imposed after tickets have been issued only if changes in the original travel plans resulted through actions of the Organization. 2. By rail 10. Unless otherwise specified on the TA, travel by rail is authorized in first class with appropriate seat reservation. This mode of travel will be made available upon request by the expert. 3. By car 11. Travel by car may be authorized only upon a request to the United Nations, but at the traveller’s own risk. Experts who travel to Geneva by car are reimbursed for fuel based on a standard rate per kilometre. The rate is subject to change without notice. The final rate awarded is calculated based on