Today, there are various forms of commercial couriers, which should be differentiated from diplomatic couriers. Often the mode of transport chosen by the courier company is usually decided by the size of the consignment and physical location of the collection and delivery points. If the collection or delivery point is in a crowded and congested city centre then on-foot couriers, bicycles and motorcycles can be used. If, however, the collection point is in a quiet suburban area or in a country place, motor cars, vans and trucks can be used. Long distances are usually covered by air and land, using road or rail networks. In some cases where the distance is less than one thousand kilometres a system is used. Here, a truck is driven from the two main centres to meet at a secure half point, like a bus station. On arrival at the central point, the trucks with their cargo of packages, letters and goods are swopped and driven back through the night so that the articles on board are ready for delivery to their final destination overnight. Courier companies have found that this kind of overnight arrangement to be more economic and reliable than air transport. Some courier companies only transport letters and smaller packages locally, so they would rely mainly on on-foot couriers, bicycles and motorcycles vehicles, whereas for larger consignments they might use vans and small lorries. These commercial couriers arose as customers found postal services relatively slow and unreliable. In certain cases where a document must be transported very quickly and safely an on-board courier is used. This courier is given the parcel or package, which is usually carried in the cabin of the aircraft. As soon as the on-board courier arrives at the goal destination he/she would exit the airport and get a taxi directly to the delivery destination. Of course, on board couriers are very expensive because the courier company has to pay someone to do the carriage plus the cost of an airline ticket. Like the major courier companies Aerospeed Couriers has on occasion delivered urgent documents by an on-board courier.