influence and minimize noise generation. Noise barriers can reduce noise pollution near built-up areas. Regulations can restrict the use of engine braking. Motor vehicle emissions contribute air pollution. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road. Road dust kicked up by vehicles may trigger allergic reactions. In addition, on-road transportation greenhouse gas emissions are the largest single cause of climate change, scientists say. Regulation Right- and left-hand traffic Traffic flows on the right or on the left side of the road depending on the country. In countries where traffic flows on the right, traffic signs are mostly on the right side of the road, roundabouts and traffic circles go counter-clockwise/anti-clockwise, and pedestrians crossing a two-way road should watch out for traffic from the left first. In countries where traffic flows on the left, the reverse is true. About 33% of the world by population drive on the left, and 67% keep right. By road distances, about 28% drive on the left, and 72% on the right, even though originally most traffic drove on the left worldwide. Economics Transport economics is used to understand both the relationship between the transport system and the wider economy and the complex network effects when there are multiple paths and competing modes for both personal and freight (road/rail/air/ferry) and where induced demand can result in increased on decreased transport levels when road provision is increased by building new roads or decreased (for example California State Route 480). Roads are generally built and maintained by the public sector using taxation although implementation may be through private contractors). or occasionally using road tolls. Public-private partnerships are a way for communities to address the rising cost by injecting private funds into the infrastructure. There are four main ones: design/build design/build/operate/maintain design/build/finance/operate build/own/operate Society depends heavily on efficient roads. In the European Union (EU) 44% of all goods are moved by trucks over roads and 85% of all people are transported by cars, buses or coaches on roads. The term was also commonly used to refer to roadsteads, waterways that lent themselves to use by shipping. Construction costs According to the New York State Thruway Authority, some sample per-mile costs to construct multi-lane roads in several US northeastern states were: Connecticut Turnpike – $3,449,000 per mile New Jersey Turnpike – $2,200,000 per mile Pennsylvania Turnpike