Transport Companies are involved various forms of transport. Some transport companies specialise in sea, land (road and rail) and air transport. Sea and freight is usually very heavy loads weighing from a dozen kilograms to many tons. Transport companies may also use less obvious forms of transport such as cable, pipeline and even space transport. Air transport companies tend to specialise in quicker movements of lighter loads. On occasion, air transport is used for heavy loads, such as airplane engines and power station components. Heavy loads are usually carried by air when there are tight deadlines. For instance if a passenger aircraft is grounded because an engine breaks down and cannot be repaired, it pays the airline to ship a new engine by air to prevent the airplane being grounded. Large aircraft are very expensive and are only productive when they are in the air. Thus, if a large passenger or freight aircraft is grounded, it is not productive and the cost of leaving it to do nothing rapidly mounts. Transport companies often specialise in carrying passengers or freight. Courier companies such as Aerospeed Couriers are specialised transport companies usually dealing with smaller items that require rapid delivery. Modern civilisation depends on having a reliable and broad and ample number of transport companies to deliver people and goods to their chosen destinations. the movement of people, animals and goods from one location to another. The infrastructure used by transport companies includes heavy engineering projects such as roads, railways, waterways and pipelines. Another important aspect needed by transport companies are various terminals like harbours, good yards, railway stations, bus stations, warehouses, pipeline terminals with storage tanks and airports. Transport companies also need access refuelling depots on land, rivers and and/or sea. Transport companies use a wide range of vehicles, trucks, motorcars, bicycles, buses, trains, helicopters, ships and barges, spacecraft and aircraft. Apart from the large number of different and varied vehicles, each form of vehicle needs special repair shops and facilities, which is an important aspect of the transport industry.