Homemade Moped

Mopeds can achieve fuel economy of over 100 mpg-US (2.4 L/100 km; 120 mpg-imp). The emissions of mopeds have been the subject of multiple studies. Studies have found that two-stroke 50 cc mopeds, with and without catalytic converters, emit ten to thirty times the hydrocarbons and particulate emissions of the outdated Euro 3 automobile standards. In the same study, four-stroke mopeds, with and without catalytic converters, emitted three to eight times the hydrocarbons and particulate emissions of the Euro 3 automobile standards. Approximate parity with automobiles was achieved with NOx emissions in these studies. Emissions performance was tested on a g/km basis and was unaffected by fuel economy. Currently in the United States, the EPA allows motorcycles, scooters, and mopeds with engine displacements less than 280cc to emit ten times the NOx and six times the CO than the median Tier II bin 5 automobile regulations. An additional air quality challenge can also arise from the use of moped and scooter transportation over automobiles, as a higher density of motorized vehicles can be supported by existing transportation infrastructure.
Racing
The wide availability of previously-used but still functional small motorcycles in western societies enables and encourages cheap forms of racing, wrongly called moped racing. Dirt-racing forms of this sport is sometimes staged in the stadiums of agricultural shows, where, unlike football and athletic grounds, the surface is not too important. One popular series uses chicanes consisting of stacked large-diameter tractor tyres and requires a team of riders, each doing ten laps and then pulling into the middle of the ring for change-over. Two heats and a final, each lasting 25 minutes, can be held in one day interspersed with speedway racing and other displays. Another series once held on full-size race-tracks, including Le Mans, ran for 25 hours (typically 3.00pm one day until 4.00pm the next) and was billed as "the longest race in the world".