section_path: Environmental performance
section_name: Environmental performance
paragraph_text: Environmental performance
  
  Careful design and construction of a road can reduce any negative environmental impacts.Water management systems can be used to reduce the effect of pollutants from roads. Rainwater and snowmelt running off of roads tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants and result in water pollution. Road runoff is a major source of nickel, copper, zinc, cadmium, lead and polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels.
  
  De-icing chemicals and sand can run off into roadsides, contaminate groundwater and pollute surface waters; and road salts can be toxic to sensitive plants and animals. Sand applied to icy roads can be ground up by traffic into fine particulates and contribute to air pollution.
  
  Roads are a chief source of noise pollution. In the early 1970s, it was recognized that design of roads can be conducted to 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.