A short-haul flight ban is a prohibition imposed by governments on airlines to establish and maintain a flight connection over a certain distance, or by organisations or companies on their employees for business travel using existing flight connections over a certain distance, in order to mitigate the environmental impact of aviation (most notably to reduce anthropogenic greenhouse gas emissions which is the leading cause of climate change). In the 21st century, several governments, organisations and companies have imposed restrictions and even prohibitions on short-haul flights, stimulating or pressuring travellers to opt for more environmentally friendly means of transportation, especially trains. A portion of air travelers in short-haul routes connect to other flights at their destination. A blanket ban would have a significant impact on these travelers, as inadequate rail connectivity between airports and main railway hubs of cities generally result in longer overall travel times and disruption to travellers overall. Flight length There is no consensus on what constitutes a 'short-haul flight'. In public discourse such as debates and surveys, the term is often not explicitly defined. The International Air Transport Association (IATA) defines a short-haul flight as 'a flight with duration of 6 hours or fewer', and a long-haul flight takes longer than 6 hours. In practice, governments and organisations have set different standards, either according to the absolute distance between cities as the crow flies in hundreds of kilometres, or in terms of how many hours it would take a train to cover the same distance. As one example, the University of Groningen set limits according to both standards, namely prohibiting its personnel from flying distances shorter than 500 kilometres, or shorter than can be travelled by train in 6 hours. There was some confusion on how to calculate and reconcile both limits: as the crow flies, the distance between Groningen and Berlin is 465 km, but the road connection 577 km; moreover, the train travel time varies from 5.