Observant commuters may notice that in some rail systems, traditional wooden ties are being replaced with those made from reinforced concrete. Concrete ties may be stronger and more durable than wooden ones, but are they environmentally friendlier?
The production of concrete, particularly the manufacture of the cement used in it, results in significant emissions of the greenhouse gas carbon dioxide. But there are also CO2 emissions related to the production and use of wooden ties.
An Australian study in the journal Environmental Science and Technology has found that, over 100 years, the carbon dioxide cost of concrete ties is lower than that of wooden ties.
Robert H. Crawford of the University of Melbourne took into account the CO2 emissions from the manufacture of both types of ties (including, for instance, emissions from mining the raw materials for concrete and from the burning or decay of wood waste) and from transportation and installation. He also factored in the decomposition of wooden ties that were replaced throughout the 100-year cycle.