The TTC is urging commuters to arrive early at Union Station because a major renovation project is expected to slow them down.

Four doors at the west end of the moat between the TTC subway station and GO Transit railway station have been closed, meaning the bottleneck between the stations has narrowed.

The doors will be closed for about eight months as construction crews continue a $640-million overhaul, which includes the construction of a new second platform and concourses.

The TTC is urging customers to leave 15 minutes early in case there are significant delays or use King Station, St. Andrew Station or the city's PATH system as alternate routes.

People can avoid lineups at Union Station by purchasing tickets, tokens and passes at any TTC collector booth, pass vending machine or more than 1,200 authorized sellers, the TTC said.

Union Station is the busiest passenger transportation facility in Canada, serving about 250,000 passengers each day. That number is expected to climb even higher in the coming years.

By adding a second subway platform and expanding the concourse to include a single TTC fare-paid area and pedestrian walkways, overcrowding will be reduced and passenger circulation will be improved, the TTC said.

The entire construction project is scheduled to be finished by 2015.

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