Will the third Heathrow runway fill up within 25 years? From a Wired article published 9 June 2018 about the proposed third Heathrow Airport runway:


  But Warnock-Smith1 warns that Heathrow will eventually fill up again unless air travel is redistributed to make use of spare capacity at other UK airports. “Otherwise in 25 years, we will be having the same debates about a fourth runway at Heathrow,” he adds.


Did Warnock-Smith base his estimate on something (e.g. a mathematical model) or was it "an off-the-cuff remark"? Have there been published studies on this topic?

1Associate head of the School for Aviation and Security at Buckinghamshire New University

Note 1: This question does not belong on Aviation.SE. (see here)

Note 2: This question does not belong on Skeptics.SE. (see here)
It is difficult for anyone here to know exactly what Warnock-Smith had in mind with his comment or whether he has conducted some analysis prior to his comment.

Nevertheless, he may be referring to the research on congestion in general, which has largely focused on road travel.

It is well-known that, contrary to popular belief, increased capacity can make congestion worse. The reason for this is so-called "induced demand". Once there is a larger capacity, a demand increase will typically follow, thereby keeping congestion at the same rate or making it even worse. One mechanism behind this increased demand is that there could be a latent demand already underlying. This means that there are consumers who want to take trips, but don't due to congestion issues. However, after the capacity increase, the realized demand increases.

This phenomenon has been observed for example with increased highway capacity, as noted in this news piece. For a literaure review on highways, see Susan Handy's 2015 article "Increasing Highway Capacity Unlikely to Relieve Traffic Congestion".