The authors of the Gateway Project have been smart to tie multiple transportation initiatives into a single broad package. By combining the good with the bad (or, at least controversial), there's a wider scope for negotiation between different municipalities and a better chance of pushing the entire package through.
Of course, it simply makes sense to consider the lower mainland's transportation system as a whole, since changes in one area will invariably affect other municipalities as well.
Among some of the positive aspects of the project: the south Fraser river perimeter road is indeed necessary for accommodating the increased truck traffic related to Deltaport, the CN intermodal yards and the US border. This will lead to increased container traffic moving through Vancouver ports, which translates into more jobs and growth.
The north Fraser perimeter road should also help with the congestion around the New Westminster area, and provide better connections to Pitt Meadows and Maple Ridge.
Furthermore, the new Pitt River Bridge foundation (bridge pictured below) will be built in such a way that it could accommodate light rail (Skytrain) in the future. The same will be the case for the Port Mann twin.
It's interesting to note however, that the creation of a Skytrain route along the Highway 1 corridor had been considered, but it was scrapped because there aren't enough regional town centres along that particular route. It's not clear whether commuter rail, similar to the Westcoast Express was considered as well.
The province also considered the idea of not twinning the Port Mann Bridge, but simply putting a toll on all traffic, as a means of reducing demand. According to the Gateway Project report (link to pdf), to create such a disincentive would require tolls to be as high as $5 to $8 per trip. Futhermore, most rerouted traffic would simply wind up diverting to the already-choked Patullo Bridge, which would remain free.
