Transport covers all journeys by road, rail, water and air, including inter-city and international travel. Greenhouse gas emissions are produced directly by the combustion of fuel or indirectly by the use of grid-supplied electricity. Collecting accurate data for transport activities, calculating emissions and allocating these emissions to cities can be a particularly challenging process. To accommodate variations in data availability, existing transportation models, and profile purposes, the GPC protocol provides flexibility in calculating emissions from transportation. Emissions from electricity used in transport such as rail travel, is included under Stationary Energy.