MONTREAL -- The Societe de transport de Montreal says it will spend almost $50 million to directly increase bus and metro service next year in an attempt to appease thousands of complaints the agency says it receives each year.

In announcing its 2020 budget Thursday, the STM says $48.6 million of its $1.6 billion operating budget - up $140 million from 2019 - will be used to implement a 2.6 per cent increase in metro service and a 5 per cent increase in bus service - the latter representing its biggest increase since 2012, the agency says.

The money will be used, among other things, to buy 300 new buses. Montreal Mayor Valerie Plante lauded the increase as an important upgrade to the STM's bus fleet.

"We're talking about a 15 per cent increase of the STM fleet which is something we have never seen before," she said.

But the increase in the number of buses will only improve bus service 5 per cent, the STM said. Partly because many of the buses will be used to deal with the closing of the Mount Royal tunnel due to construction of the REM light-rail project.

The STM will expand its '5 minutes max' metro service guarantee throughout the year. (Currently it is not offered during the summer.) It will also be adding 17 new Azur trains, which will mean that 80 per cent of the Green Line will be served by the newer model metro cars.

At Thursday's budget announcement, STM director-general Luc Tremblay and Mayor Valerie Plante also acknowledged that the STM was experiencing a shortage of buses on the road, which is affecting service to the public, and that the transit agency was working to fix the issue.

They said the STM on Thursday was 140 buses short of having enough buses on the roads to meet the needs of its posted schedules.

The news comes a day after a union representing STM workers said a glitch with a new STM computer system was responsible for keeping many buses off the road.