2017 - Research

Climate change, weather and road deaths

Key takeaway:

  • More road deaths occur on warmer or wetter days. There was an unusual and sudden spike in road deaths in the US in 2015, which reversed a downward trend in road deaths over the past 35 years. Author argues that the 2015 road death spike is associated with the unusual temperature rise from 2014 to 2015.

Results:

  • Road deaths in the US increased by seven percent from 2014 to 2015, which marked an abrupt reversal of the downward trend in road deaths that has persisted for the past 35 years.
  • The author attributes this anomalous spike in road deaths from 2014 to 2015 to a 1.5 degree Fahrenheit temperature rise from 2014 to 2015, which was unusually large and likely induced by climate change.
  • There is a positive correlation between rising temperatures and driving: For each degree increase in temperature, vehicles were driven an extra 60 miles per person per year. Increased vehicle miles increase carbon emissions, thereby creating a classic feedback system: more miles, more carbon, more warming, more miles.
  • There is also a positive correlation between increased rainfall and driving: For each additional inch of rainfall, vehicles were driven an extra 66 miles per person.
  • The rate of road deaths is higher in counties with higher temperatures and higher rainfall.
  • People are also more likely to walk and bike when it’s warmer, which could increase their risk to road injuries and fatalities. However, there is a lack of data on relationship between people walking/bicycling and temperature.
  • Counties with higher average household incomes tended to have lower road deaths rates. This could be because more people can afford newer models of cars with more safety features.
  • As temperatures continue rising from heat-trapping atmospheric gases, road deaths will likely increase more than expected unless preventive measures to reduce road injuries and fatalities are adopted.

Implications:

  • More research could be done on the relationship between temperature and active modes of transportation (walking and bicycling).
  • The correlation between rising temperatures and driving, as well as rising temperatures and road deaths, underscores the necessity of safe, quality infrastructure that promotes walking and cycling (i.e., protected bike lanes that are separated from road traffic).

Methods:

  • The author examined two large datasets: One allowed him to analyze the association of temperature and rainfall on the annual miles driven per person in US urban areas; the other allowed him to assess weather and other factors to the risk of road deaths in the 100 most densely populated US counties.

Robertson, L. (2017). Climate change, weather and road deaths. Injury Prevention