What they're saying is that there will be just as many cars on the road as before and therefore not reducing the environmental impact of the road. I imagined i

What they're saying is that there will be just as many cars on the road as before and therefore not reducing the environmental impact of the road. I imagined it to be something like this: Old: - Road: 1000 users - Train tunnel: 1000 users New: - Road: 1000 users - Train: 2000 users Although the train is more environmentally friendly than the road, I think the article is saying the impact of adding it is just that more people make the trip rather than the same number of people doing it in a more environmentally friendly way. This is basically the concept of induced demand i.e. build it and they will come.