When it comes to renovations, there are always surprises and the situation is no different at Toronto's Union Station, where designers didn't account for the size of new GO trains. 

Just a few inches are causing major design headaches for the province's transportation agency, Metrolinx, which has to rethink renovation plans for the GO train platform at the station to accommodate the taller electric trains coming into service in the next several years.

"It's just a matter of a couple of inches," Metrolinx spokeperson Anne Marie Aikins said. "It's not too much."

The City of Toronto's portion of the  Union Station revitalization work has been plagued by delays and is already around $160 million over the original $640 million budget. But Metrolinx said its portion of the renovation work — which includes new staircases, additional vertical access points, and an overhaul of the platforms and station concourses — is on time so far. 

Now, experts must decide whether to raise the 90-year-old historic shed's roof or lower its rails so that new trains will have enough clearance.

Metrolinx could not say what what delays or costs might be incurred by the redesign, saying both will depend on what option the experts ultimately determine is best.

"Unfortunately the people that built Union Station weren't thinking in terms of electrifying a service. They had diesel trains and that's what they accommodated," Aikins said.  

On the plus side, said Aikins, when Metrolinx received funding for renovations last year, the shed's roof wasn't put back on so engineers won't need to redo that.

"No other work has to be undone so we didn't waste any money or time or effort — so great news," Aikins said.

Transit users have mixed feelings about the prospect of further delays to Union Station's renovations.

"I think it would be a lot smarter and more convenient to change the size of the train. Make it smaller by a couple of inches. It would be cheaper than changing the whole building," customer Kaelyn Schindell said.

Rider Eva Amos got married in Union Station's Oak Room 50 years ago. "Is it going to make it better for everyone?" she asked. "If it is, bite the bullet and get on with it."

GO hopes to electrify all of its transit lines by 2024.