Air transport is the costliest and most modern means of transport because it involves the use of airplanes, which are expensive to manufacture, operate, and maintain. Air transport offers the fastest and most efficient mode of transportation, allowing people and goods to be transported across long distances in a relatively short amount of time. Additionally, air transport provides convenience and accessibility, as it allows for travel to remote locations and enables global connectivity. However, the high costs associated with air transport, including fuel, infrastructure, and security, make it the most expensive mode of transportation.