A UK study, published in 2009, found that on average women suffer four times as much psychological stress from their work commute as men do. Institutions that have few dormitories or low student housing populations are called "commuter schools" in the United States. Most commuters travel at the same time of day, resulting in the morning and evening rush hours, with congestion on roads and public transport systems not designed or maintained well enough to cope with the peak demands. As an example, Interstate 405 located in Southern California is one of the busiest freeways in the United States. Commuters may sit up to two hours in traffic during rush hour. Construction work or collisions on the freeway distract and slow down commuters, contributing to even longer delays. Cars carrying only one occupant use fuel and roads less efficiently than shared cars or public transport, and increase traffic congestion. Commuting by car is a major factor contributing to air pollution. Carpool lanes can help commuters reach their destinations more quickly, encourage people to socialize, and spend time together, while reducing air pollution. Some governments and employers have introduced employee travel reduction programs that encourage such alternatives as car-pooling and telecommuting. Some are also carpooling using Internet sites to save money. Alternatives like personal rapid transit have also been proposed to reap the energy-efficiency benefits of a mass transit system while maintaining the speed and convenience of individual transport. Traffic emissions, such as from trucks, buses, and automobiles, also contribute. Airborne by-products from vehicle exhaust systems cause air pollution and are a major ingredient in the creation of smog in some large cities. The major culprits from transportation sources are carbon monoxide (CO), nitrogen oxides (NO and NOx), volatile organic compounds, sulfur dioxide, and hydrocarbons. (Hydrocarbons are the main components of petroleum fuels such as gasoline and diesel fuel.) These molecules react with sunlight, heat, ammonia, moisture, and other compounds to form the noxious vapours, ground level ozone, and particles that comprise smog. In the United States, the Census Bureau's American Community Survey (ACS) collects data on commuting times, allowing an analysis of average commute time by industry, location, and vehicle. According to the 2014 ACS, the average commute time for adults in the United States was 26.8 minutes. The occupations with the longest commutes were Construction and Mining (33.4 minutes), Computer Science and Math (31.8), and Business Operations Specialists (30.2), while those in the military had the shortest commute (21).