Some napkin math: There are ~2.5 million miles of highways in the United States, for the sake of easier math and a lack of statistics let us assume that this l

Some napkin math: There are ~2.5 million miles of highways in the United States, for the sake of easier math and a lack of statistics let us assume that this length of pavement is responsible for all of the vehicular nitrous oxide emissions. Transportation contributes 30% of total NOx emissions [2]. Lets assume that the average highway is 4 lanes wide, giving a width of 62 feet. Surface area = 2.5 million miles * 62 feet = 29 356 square miles. The authors add 2.67 g per square meter of C-doped TiO2 (which has a lowball estimated cost of ~$750 per metric ton.) This gives us 203 000 tonnes or ~$150 million. This has to be applied 3x a year (at least) to maintain ~%60 of maximal effectiveness of the TiO2 (20%) over the year. A generous estimate is that it is sunny ~1/3 of the time. So to bring it all together, $450 million of raw materials would result in a (1/3 * 60% * 20% * 30%) 1.18% reduction in NOx levels. [1] Original Article: http://dx.doi.org/10.1016/j.jhazmat.2013.02.012 http://dx.doi.org/10.1016/j.jhazmat.2013.02.012 (behind a paywall) [2] http://epa.gov/climatechange/ghgemissions/gases/n2o.html http://epa.gov/climatechange/ghgemissions/gases/n2o.html Edit: Updated math, I used the wrong percentage of the contribution of motor vehicle traffic, the correct figure is 30%, nevertheless the conclusion that this would be a colossal waste of money still stands.