The renovation of Union Station is, let's face it, a big pain. The ongoing, seemingly endless construction is snarling traffic, annoying commuters and turning the busy precinct in and around the station into a vast work site.

The expense is massive and rising. A report going to a city hall committee next week says that the cost of maintaining heritage features and keeping the facility open during construction has added $80-million to the price tag, leaving the current bill at nearly $800-million.

But, goodness, what a marvel Union Station is – a Beaux-Arts beauty in the heart of the city – and what potential it holds. This project promises not only to ease daily life for life for throngs of commuters and restore the time-worn building to its former glory, but to transform the centre of the city. The station is a key to Toronto's future as a modern metropolis, with efficient mass transit and a dense, vital downtown. It should galvanize Toronto's already teeming core, making living, working and visiting easier and more attractive.

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A tour around the building shows the scope and ambition of the refit. The colonnade out front is covered for cleaning and restoration (see sidebar). In the moat below, workers are laying the groundwork for a new pedestrian passageway with a glass roof. In the train shed, where trains pick up and disgorge passengers, a vast glass atrium supported by 48 leaning steel struts is rising over the old structure to bring in light and open up the space. Underneath it all, engineers have reinforced more than 100 concrete columns to support the revamped station, including a new level with high-end shopping and restaurants.

One reason the construction is taking so long and costing so much is that workers have to protect and restore its many heritage features. They include a barrel-vaulted ceiling of Guastavino tile, floors of Tennessee marble and 22 Tuscan Doric pillars weighing 75 tons each and fashioned on a giant lathe. Even the radiator covers, mail chutes, and brass door fittings are considered precious.

From the beginning, Union embodied Toronto's dreams. Building it on the wasteland left by the Great Fire of 1904 was a bet on the city's success. "Do we really believe in the city of Toronto?" asked banker Byron Edmund Walker in 1906. "Do we believe it is going to be one of the great cities of North America?"

City fathers decided that they did. Plans were drawn up in 1913 to tear down the old Union Station, the second in the city to bear that name, and replace it with a third, much grander edifice. When the Prince of Wales finally opened the building officially on Aug. 6, 1927, after years of delays caused by strikes and the outbreak of the First World War, the city was thrilled. "New Union Station hums with life today" read one of the banner headlines that appeared when the station threw open its doors.

This was the height of the railway era, when there was talk of two more transcontinental railways. A train station was where you came to worship the twin gods of rail and progress. Two years later, the Royal York hotel opened across the street to match Union for grandeur. Countless immigrants passed through the station's Great Hall, and tens of thousands of soldiers said farewell to their families on their way to fight in the Second World War. In time, Union became what author Pierre Berton called "the soul and heartbeat of Toronto."

But the heartbeat slowed as highways and airlines replaced rail as the main conduit for inter-city travel. Starved of investment, poorly maintained, Union grew sooty and shabby. Renovations to its underbelly steered commuters out of its Great Hall – at first prosaically named the Ticket Lobby – and through an ugly, crowded underground concourse.

Now the old station in on the verge of a glorious rebirth.

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Union is already the busiest transportation centre in the country. The renovation, jointly funded by the federal, provincial and city governments, is designed to restore, expand and improve it for future growth.

In place of its original purpose as a passenger railway terminus, it has become a busy hub for the highly successful and rapidly growing GO commuter rail service. It sweeps 200,000 people through Union every day on 240 trains. Passenger traffic is expected to double or even triple by 2031 as GO expands from a rush-hour service to an all-day transit network like the urban railways of Paris or Tokyo.

The rage for downtown living can only fuel the traffic. Forecasters expect the downtown population to grow 80 per cent to 130,000 by 2031. With the financial district just to the north and the new high-rise South Core on the other side, Union is right at the centre.

The big renovation, now in the fourth year of a six-year schedule, seeks to turn it into a bigger and more efficient transfer point. New underground concourses will give travelers on foot a cleaner, quicker route to where they are going. A new connection to the PATH network will help, too.

A new train, the Union-Pearson Express, will whisk travelers to and from the airport. A second subway platform will make connections to the TTC much better.

Union will become a true hub, with spokes going out in all directions in various modes. Passengers trains, GO buses, commuter trains, the airport train, the subway, the streetcar to the west (and, with luck, one day the east) harbourfront -- all will go through Union.

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The growing foot traffic will flow in all directions, too -- to the sports stadiums, to the bank and office towers, to the new attractions of the waterfront, to the CN Tower and aquarium. Few cities are lucky enough to have so much, so close to their central transportation hub.

In the meantime, it is indeed a mess. When news of the cost overruns broke this week, Doug Ford and other city councillors called it a frustrating case of government inefficiency.

But, as Byron Edmund Walker asked, "Do we really believe in the city of Toronto?" If the answer is yes, then we should swallow our irritation and cheer the the big reno at Union Station.