Good luck getting the MTO to go along with it.
The Region of Waterloo has repeatedly approached the MTO about combining the proposed 4 lane road bridge south of the existing structure with an LRT crossing of the Grand River and placing the LRT in the highway corridor. In both cases, MTO has refused.
They say that it's a safety issue, having vehicles on a fixed track beside ones with drivers; That overhead wires would be a distraction; That if an accident ever did occur on the LRT line, it would require lane closures, That if an accident were to occur on Highway 8, the LRT ROW would get in the way, once even citing that an LRT corridor through this area would interfere with the placement of their high mast lighting.
And so, the LRT corridor was pushed northward into an existing rail corridor which serves Toyota and would need to be relocated. This would also require the further relocation of endangered mussels further upstream for the reconstruction of the existing bridge or the construction of a parallel structure.
All of the challenges presented by the MTO are easily technically overcome; higher barriers between traffic and LRT, moved lighting fixtures, Moitoring of traffic on highway 8, and quick signalling in case of accidents, ect. The environmental impact, temporal, and cost benefits of placing the LRT and Highway 8 on the same structure outweigh the technical challenges and cost of property acquisition and contruction associated with relocating a rail corridor.
We must remember, the MTO's job is building roads. It takes a lot of arm twisting to get the MTO to do anything that could possibly reduce their need to design and build roads. While a 401 rapid transit corridor is definitely technically feasible and could be beneficial, I don't expect the MTO to go along with it, unless its BRT, in which case, they'd probably be all for it as all you would really need to get started is some paint, some bus shelters, and some stairs.
For the uninitiated,
here's the map of the area. Highway is is planned to be widened from 4 lanes to 8 lanes featuring a new bridge over the Grand River south of the existing structure. The parallel rail corridor is located immediately north sandwiched between King Street and low density residential.