Wherever they put it, they should overspec the bridge for loading and build it such that it can have capacity and capability to be added on into the future.
Longevity should be a consideration as well. It can’t be unnoticed that the Macdonald Bridge, which is a quarter century older than the MacKay, has been modified for increased capacity, and there is no discussion that I’m aware of that is indicating an end to its lifespan. Meanwhile, it’s well known that the MacKay was built on the cheap and thus can’t be added to, is at the end of its service life, and now has to be replaced.
Some significant investment now will save big in the future.