One of the most severe problems hampering road safety in today's world is traffic congestion.

According to a study conducted by the Boston Consulting Group (BCG), traffic congestion during peak hours in four major cities, Delhi, Mumbai, Bengaluru and Kolkata costs the economy ₹1.47 lakh crore annually. The peak hours for this survey were 7 to 9 am and 6 to 8 pm during which commuters spent about one-and-a-half times longer to travel a given distance as compared to non-peak hours, said the report by BCG.

Traffic congestion occurs when the amount of vehicles on roads out par the capacity. This results in slower speeds, longer trip times, and increased vehicular queueing. Traffic congestion also leads to frustration and road rage. Congestion lowers vehicle speeds resulting in an increase in pollutant concentrations from roadway. Congestion can increase risks for individuals driving on freeways and arterial roads, and for individuals living or working near roads.

Traffic built up has major impact on human health. The Wall Street Journal in an article said that as per new public-health studies and laboratory experiments, at every stage of life, traffic fumes exact a measurable toll on mental capacity, intelligence and emotional stability.

According to a CNN report, a study by Washington University noted that long commutes eat up exercise time. Thus, associating long commutes with higher weight, lower fitness levels, and higher blood pressure that are all strong predictors of heart disease, diabetes, and certain types of cancer. The study also notes that "being exposed to the daily hassles of traffic can lead to higher chronic stress." Stress, is termed as a silent killer that makes people vulnerable to a number of other diseases including depression.

Other than stress, people also face exposure to pollutants that affect the lungs, especially pedestrians and those riding in non air-conditioned vehicles such as motorcycles. The World Health Organization (WHO) said that air pollution is to blame for 3.2 million preventable deaths worldwide every year.

Commuters caught in the traffic mess also tend to be deprived of sleep, especially those who have to get up early the next day to be able to get to work on time. An article by The Telegraph said that a week with less than six hours of sleep each night can lead to 711 changes in how genes work.

Sleep deprivation can affect performance, attention, and long-term memory by causing anxiety, exhaustion, frustration, impulsive behaviour, lower immunity, and mental health problems.

Scientists in the Netherlands discovered that breathing street-level fumes for just 30 minutes can intensify electrical activity in brain regions responsible for behaviour, personality, and decision-making, changes that are suggestive of stress.

Children in areas affected by high levels of emissions, on average, scored more poorly on intelligence tests and were more prone to depression, anxiety and attention problems than children growing up in cleaner air, separate research teams in New York, Boston, Beijing, and Krakow, Poland, found.

Older men and women long exposed to higher levels of traffic-related particles and ozone had memory and reasoning problems that effectively added five years to their mental age, researchers in Boston reported. The emissions may also heighten the risk of Alzheimer's disease and speed the effects of Parkinson's disease.