For National Transportation Week, road, rail, air compared

By presidential proclamation, President Barack Obama on May 9, 2014 declared the week of May 11th through May 17th as National Transportation Week 2014.

With this in mind what better time is there than right now to talk transportation?

For all regular Air Quality Matters blog readers paying close attention since Day-1 (Nov. 5, 2012), all should be well aware that the majority of posted articles deal with transportation with, of course, there being a connection to air.

360px-CBX_Parkchester_6_jeh[1]Not surprisingly, transportation contributes the most toward world air pollution and, therefore, the amount of press given here on transportation topics.

In fact, related to this, the International Union of Railways (UIC) in its Nov. 2011 High Speed Rail and Sustainability report wrote:

“Over 50% of the world’s emissions of carbon monoxide, hydrocarbons and nitrogen oxides caused by burning fossil fuels are produced by petrol and diesel engines. …”

“In the United Kingdom for instance, it is estimated that up to 24,000 people die prematurely every year as a result of poor air quality, mainly due to individual road transport. Regulated emissions from transport have decreased significantly since 2003: PM10 by 30%, acidifying substances (mainly SOx and NOx) by 34% and ozone depletion substances by 40%. Nevertheless, local air pollution, in particular from road transport, remains a major hazard.”1

Negative air impact: A mode-by-mode-by-mode comparison

One of the chief considerations when discussing transportation is the quantification of emitted pollutants; in other words, how much of what type of pollutant is being emitted one mode compared with others? For illustrative purposes, compared are airplane (A), car (C) and high-speed train (HST) for the following pollutants: Carbon dioxide (CO2), particulate matter (PM), sulphur dioxide (SO2), nitrogen oxides (NOx) and non-methane hydrocarbons (NMHC).

The information below is referenced from “Figure 11 A modal comparison of air pollutant emissions.”2 Please keep in mind CO2 is measured in kilograms (kg) while all other pollutants are measured in grams (g). Please also note that the Frankfurt to Hamburg route in Germany was selected and the “Characteristics and components” are expressed in “units per person travelling.”

  • CO2 – 77.1 (A), 86.0 (C), 19.2 (HST)
  • PM – 2.1 (A), 21.2 (C), 1.0 (HST)
  • SO2 – 43.4 (A), 3.2 (C), 19.5 (HST)
  • NOx – 268.3 (A), 223 (C), 17.2 (HST)
  • NMHC – 20.8 (A), 18.3 (C), 1.1 (HST)

To sum up, only for particulate matter, are airplane and high-speed train comparable. For sulphur dioxide, for “units per person travelling,” the car is the least polluting, while for carbon dioxide, nitrogen oxides and non-methane hydrocarbons, for “units per person travelling,” high-speed train is the most environmentally friendly.

Among air and land transportation modes, if evaluated solely on the basis of being the least damaging to the air overall and that is used as the primary determining criteria with respect to selection, high-speed train wins hands down.

But, to be fair, motor vehicle travel could be quite competitive in this regard provided there is a proliferation (read: “an uptick of almost unimaginable scale”) in non-polluting (zero-emissions) car and truck use. At the same time, this would necessitate a corresponding drop in combustion vehicle operation of unprecedented proportions.

Though not impossible, at this time something on this order is not likely.

Nonetheless, the prospect is an interesting one to consider, especially considering National Transportation Week being this week.


  1. High Speed Rail and Sustainability, “Air pollution,” International Union of Railways (UIC), Nov. 2011, p. 21.
  2. Ibid, “Figure 11 A modal comparison of air pollutant emissions,” p. 22.

This post was last revised on Oct. 5, 2020 @ 7:14 a.m. Pacific Daylight Time.

Published by Alan Kandel