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Many articles on the internet claim that living near highways can be harmful to one's health. Here is an example:

All told, cursory internet research suggests that several studies have been done on the subject, and they have found that living near highways can increase the risk of the following health problems:

  • Dementia (as described in the above article)
  • Cardiovascular disease
  • Impaired lung function
  • Asthma (particularly in children)

The studies all suggest that these health problems are caused by air pollution, usually in the form of ultrafine airborne particulate.

Given that, what is a reasonable safe distance to live away from a highway in order to reduce or eliminate the above health risks?

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To answer this question you would need to find the source of the information. I found the study mentioned in the article in the Toronto Star (Chen, et al. 2017); and while studying risks of dementia, Parkinson's disease and multiple sclerosis, with emphasis mine, they said:

In this population-based cohort study, we assembled two population-based cohorts including all adults aged 20–50 years (about 4·4 million; multiple sclerosis cohort) and all adults aged 55–85 years (about 2·2 million; dementia or Parkinson's disease cohort) who resided in Ontario, Canada on April 1, 2001. Eligible patients were free of these neurological diseases, Ontario residents for 5 years or longer, and Canadian-born.

Between 2001, and 2012, they identified

  • 243,611 incident cases of dementia,
  • 31,577 cases of Parkinson's disease, and
  • 9,247 cases of multiple sclerosis.

They provided adjusted hazard ratios in the study - a comparison of the effect of different variables on survival or other outcomes that develop over time (Dawson, 2008). See also https://www.sciencedirect.com/topics/medicine-and-dentistry/hazard-ratio

The adjusted hazard ratio of incident dementia was

  • 1·07 for people living less than 50 m from a major traffic road (95% CI 1·06–1·08),
  • 1·04 (1·02–1·05) for 50–100 m,
  • 1·02 (1·01–1·03) for 101–200 m, and
  • 1·00 (0·99–1·01) for 201–300 m versus further than 300 m (p for trend=0·0349).

No association was found with Parkinson's disease or multiple sclerosis.

Based on the averages used in the study, statistically speaking you will need to be living at least 200 metres (just over 218.5 yards) away from any major road to be relatively free of risk.

References

Chen, H., Kwong, J. C., Copes, R., Tu, K., Villeneuve, P. J., Van Donkelaar, A., ... & Wilton, A. S. (2017). Living near major roads and the incidence of dementia, Parkinson's disease, and multiple sclerosis: a population-based cohort study. The Lancet, 389(10070), 718-726.
DOI: 10.1016/S0140-6736(16)32399-6

Dawson, G. F. (2008). Measures of Effect. In: Easy Interpretation of Biostatistics: The Vital Link to Applying Evidence in Medical Decisions. Philadelphia, PA: Saunders
DOI: 10.1016/B978-1-4160-3142-0.50027-4 (Free Preview)

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  • HR of 1 at greater than 200 m
    – Graham Chiu
    Apr 6, 2018 at 9:00
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    A Hazard Ratio of 1.0 means that there is no increased risk. So, the answer is to live more than 200m away from the highways.
    – Graham Chiu
    Apr 6, 2018 at 9:33
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    I have sat down and re-read the data presented and agree you are right. I misread it earlier and the answer is to live further than 200 metres away.
    – Chris Rogers
    Apr 7, 2018 at 0:11
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There are many factors to consider. The pollution level (and risk) depends on at least the following:

  • typical wind direction during rush hour
  • density of trees between you and the road
  • elevation difference between you and the road
  • presence of a noise wall between you and the road
  • level and type of traffic on the road

This page aggregated a large number of studies to try to answer this and settled on greater than 300 meters. Based on the studies cited in it and everything I've seen, that seems reasonable.

http://blog.cityprojections.com/2018/12/how-far-should-you-live-from-road-to.html

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This is tough question to answer because it depends so much on the exact location, the type of highway, how busy it is, and the surrounding vegetation, structures, wind, etc.

Pollution is mainly measured not only by the types of chemical and compounds in the air, but also by their size... as in Particulate Matter PM2.5, and P10 which denotes how large the particles they are. In most countries there does occur air-quality monitoring in some locations. However, when it comes to particulate matter, there is a the dose-response which indicated that there is no level where health effects do not occur.

Furthermore, it's not just cars that this pollution comes form, as they can occur naturally or in industrial areas. For example, I live in a mining town, and we measure air quality on a regular basis due to the coal dust which blows over from the mines and settles over the town.

The exact answer to 'how far away' cannot be answered for definite. You should live a location where the air-quality is well within the national standards for your country (if you have any).

At the very least, the further away the better, at least 1km would take you out of the higher risk zones.

References:

[1].http://npi.gov.au/resource/particulate-matter-pm10-and-pm25 [2].https://sandiego.urbdezine.com/2015/05/28/what-is-a-safe-distance-to-live-or-work-near-high-auto-emission-roads/

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    1km is a large distance. Where did you get that figure from? The sandiego.urbdezine report you linked stated that the high toxicity zone = 300 – 500 feet. A more recent study (referred to in the OPs link) suggests further, but not by that much - See my answer
    – Chris Rogers
    Apr 6, 2018 at 7:37

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