Environment and safety

The places where people live and travel affect their health and survival alongside personal habits and medical care. This section covers two parts of that environment: the natural surroundings near home, and the risk of injury and death on the road. Both are studied mainly through large population records rather than randomised trials (studies that assign people to groups by chance), because neither neighbourhoods nor travel habits can easily be assigned.

Green space is land covered by vegetation, such as parks, woods and gardens. In a meta-analysis (a study that pools the results of earlier studies) of 9 studies and more than 8.3 million people, each 0.1-unit increase in satellite-measured greenness (a vegetation index where higher means greener) near home was associated with 4% lower all-cause mortality (death from any cause) [1]. The largest single study, of 4,645,581 adults in London, found no association with overall green coverage but lower mortality where there were more small local parks [2]. In England, the gap in death rates between richer and poorer people was smaller in greener areas [3].

Road safety covers the causes and prevention of deaths and injuries in traffic crashes. In the United States, 43,273 people died in motor vehicle traffic crashes in 2023 [4]. In a study that recorded more than 3,500 drivers on video, driver error, impairment, fatigue or distraction was present in almost 90% of crashes [5]. Protective equipment has large effects: seat belts reduce the risk of death for front-seat car occupants by 45% [6].