Eric Morris recently wrote a post for Freakonomics that attempts to evaluate some of the proposed benefits of a high-speed rail system. In it, he cited a study commissioned by the U.K. Department for Transport, casting doubt on claims that high-speed rail will be an environmentally friendly alternative to other forms of transportation. Morris wrote:

Booz Allen considered two potential U.K. HSR lines (London-Manchester and London-Edinburgh/Glasgow). They found that the CO₂ emissions required to move HSR passenger seats were about the same as those required to move automobile seats — hardly a slam dunk for rail. In fact, intercity bus came out considerably cleaner than HSR on a per-seat-mile basis.

HSR would emit less on a per-seat mile basis than air travel. But the major caveat is that all of these figures consider emissions from operations only, without taking into account the very large amount of pollution that will be created in the construction of the HSR system. [...]

[Given] 100 percent rail ridership, emissions over a 60-year period would be lower if the HSR line was never built.

Keep in mind that this study focuses on high speed rail projects in England, but “given its high population density and short distances, Britain may actually be a better place for HSR than most areas of our country.”

It is worth noting that this study assumes static technological progress. This is not a fatal flaw. Assuming that technology will improve in the coming years and lead to lower environmental harm by way of trains, it is reasonable to conclude that this technological change would be widespread and trans-industrial. If historical trends are any indication, technological gains will be realized and implemented quicker and with more ease in airlines and automobiles, and at a pace that will continually outstrip the meager gains that trains will achieve.

The bottom line here is that for high-speed rail expansion to be at all environmentally friendly, ridership will have to spike to numbers that we can’t reasonably expect. This is an important realization, and is one that casts considerable doubt on claims that high speed rail is a necessary step to show true support for the environment.