Transit riders forced to squeeze through the front doors of crowded 504 King streetcars will soon be able to board the vehicles from the back.

Currently, riders have to board the cars that run along King Street from the front, where they must display their passes or transfer slips to the driver.

Starting Jan. 1, those with passes and transfers can board from the back, based on the honour system, from morning to evening. Though riders can board without showing proof of payment, they may be asked to show their passes or transfers to TTC transit enforcement officers who will monitor the line.

All-door boarding is expected to shave five to six minutes off the total time the route takes, Toronto Mayor John Tory said Monday at a news conference with new TTC Chair Josh Colle and TTC CEO Andy Byford.

The 504 line is the city's busiest surface route, carrying 60,000 people each day, Tory said.

"Why is this significant? Almost 20 per cent of the streetcar's trip is spent servicing stops," Tory told reporters.

"By moving to proof-of-payment, we can cut that time in half."

Tory said the system relies on Toronto residents paying their fares. There will be "no mercy" for those who skip the payment, he said.

When asked about riders who are already boarding from the back doors, Byford told reporters that it does happen along King Street, but drivers are asked to exercise discretion. Most drivers only allow back-door boarding when the front doors are blocked by other users, often during rush hours.

Starting Jan. 1, Byford said all riders will be allowed to board from the back, regardless of how crowded a car is. It will become the standard practice on the 504 King line from 7 a.m. to 7 p.m. going forward.

Byford said the TTC is looking into other solutions to increase efficiency along King Street, including transit priority signals, but did not provide a timeline.