The TTC is running "ghost" trains on its Line 1 extension between Sheppard West and Vaughan Metropolitan Centre stations starting on Sunday as the transit agency tests its soon-to-be-opened service.

The Line 1 extension, at a cost of $3.1 billion, is slated to open on Dec. 17, linking Toronto to York Region.

Heather Brown, spokesperson for the TTC, said the testing of the new extension is allowing operators to become familiar with the six new stations along the 8.6 kilometres of new track.

It is also allowing the TTC to test its signalling system along the extension and timing from Finch station to the end of the new line. And it is giving operators a sense of what passengers will experience when the extension opens to the public.

A look inside the new Vaughan Metropolitan Centre station. (CBC) "Starting today, we are running ghost service along our new Line 1 extension service," Brown said on Sunday. "Customers will get off at Sheppard West station but the trains will continue up the line."

One operator and one guard are on each of the "ghost" trains, or trains without customers.

Trains are heading north from Sheppard West station to the Vaughan Metropolitan Centre station, which the TTC says takes 12 minutes. From there, the trains are heading south back to Sheppard West station, where passengers are being picked up as the trains make their way to Finch station.

The training is a simulation of regular service, Brown said.

"The operators will stop at each of the stations and they do this to familiarize themselves with where they need to stop in the stations. They'll open the doors and mimic as if customers are getting off. They'll close the doors and they'll go to the next station. And that will happen right up until the end of the line," she said.

A look at the outside of the Vaughan Metropolitan Centre station. (CBC) "This just gives them an opportunity to get a sense of what the timing will feel like in the stations."

The training will run right up until Dec. 17. It began at 8 a.m. on Sunday and is expected to finish for the day at 2 a.m. For the next 21 days, the TTC is testing its extension.

TTC operators have three weeks to become familiar with the extension. Brown said the testing is designed to ensure service is reliable when the extension opens to the public.

The TTC is also timing the service between stations for planning purposes and will adjust the timing if need be to maintain service levels.

Also starting on Sunday, customers will exit on the northbound side of the platform at Sheppard West station and board only on the southbound side. Barricades are set up and TTC staff are directing customers to help them adjust to the change.

Outgoing TTC CEO Andy Byford will open the new Line 1 extension before stepping down to take a job with New York City Transit. (CBC) The six new stations on the Line 1 extension are: Vaughan Metropolitan Centre, Highway 407, Pioneer Village, York University, Finch West and Downsview Park. All have new Presto fare gates.

Sheppard West, formerly Downsview, is the next existing station in the line.

"These stations are new to the Line 1 system. It opens a whole new world of transit for people north of Steeles Avenue who would have typically taken the bus to our stations," Brown said.

"These people can now hop onto a subway and come down into Toronto using the subway, which is a much faster journey than travelling on a bus and then transferring to a subway."