I used to be against the idea of the Gateway Program altogether, but now that it's in construction, I can only offer suggestions to make its use as efficient as possible.
One of the main reasons for the Gateway Program is to help facilitate the movement of goods from the interior to the ports: specifically, to help trucks quickly get from the far end of the Valley to the coast, either at Metro Vancouver, North Vancouver, Tsawassen, or the Roberts Superport.
While trucks might see slightly better congestion management immediately, the sad fact of the matter is that in five years' time, the trucks are going to be battling the same level of congestion on major routes throughout the region, leading to the same delays in freight traffic and the same losses that have been worrying the BC Ministry of Transportation this whole time. Automobile Traffic fills most of the space it is given, unless careful mitigation of land use or travel restrictions is involved, or the city spends ridiculous amounts of money continually expanding the network. (Houston has been able to decrease congestion relative to other American cities while spending $1 billion per year for 15 years. That's 5 Gateway Programs, or 15 South Fraser Perimeter Roads over 15 years, or enough transit to put every city in Metro Van on Skytrain, [or build out an amazing regional rail system to Hope (via the interurban), run medium-speed trains to Whistler (75 minute travel time), and fund the rehabilitation of the passenger railway corridor to the US border to accommodate 300 km/h High Speed Rail to Seattle]. However, the $15 billion price tag doesn't nearly account for the environmental and social effects of the induced sprawl.)
From the above study:
"The problems people associate with roads - congestion, air pollution, and the like - are not the fault of road investments per se. These problems stem mainly from the unborne externalities from the use of roads, new and old alike..."
So why not mitigate the new roads - North Fraser Perimeter Road, South Fraser Perimeter Road, and Highway 1 improvements - by effective tolling and/or truck-only lanes? The relative importance of a truck full of time-sensitive shipments is much higher than that of one average commuter (or three to four, if you want to define it by the size of a truck) - so why don't we let the trucks have priority? This would ensure long-term usability of the new roads specifically for the freight sector, which needs the Gateway Project the most.
The "plight" of car commuters, however, will only be eased with strict land development regulations along the corridor, a new strong regional transit network that provides a viable and useful alternative to the current automobile-exclusive infrastructure, and perhaps a tolling system which will allow the people who need to commute by car the most (highest willingness-to-pay) to have access to swift-moving, decongested roads? The two developments (tolling the highways and improving transit) need to happen at the same rate and at the same time. Tolls shouldn't be raised if transit is not improved at the exact same time. Funding scheme for Translink, anyone? Anyone?
The idea of separating trucks and cars has been supported in depth by these folks and these folks too. Take a look.