Tearing down the eastern portion of the Gardiner Expressway could add an extra 10 minutes to drivers' morning commutes, according to a newly-released report.

The report, released Thursday, was written by the University of Toronto's Centre for Intelligent Transportation Systems and commissioned by the Gardiner Coalition.

Its authors were asked examine the potential impact of removing a crumbling section of the roadway, and to assign a dollar value to lost productivity.

Researchers found that travel time could increase by approximately five or 10 minutes should the city opt to demolish a section of the aging expressway between Lower Jarvis Street and Logan Avenue.

With an increase in traffic congestion on alternative routes, the cost of lost productivity due to the delay would add up to between $23.4 million and $36.3 million per year, according to the report.

Last month, the city revealed the official cost estimates of three options for the six-lane, 2.4-kilometre stretch of aging roadway.

The first option is to remove the raised portion altogether, creating an eight-lane ground-level alternative. The official assessment pegged the total cost at $461 million, and said it would increase travel time by an average of three to five minutes.

The city also suggested maintaining the expressway, with an $864 million price tag, or creating a "hybrid alternative," that would cost $919 million. The hybrid option would maintain some type of expressway link between the Gardiner and the Don Valley Parkway, and would widen Lake Shore Boulevard from six lanes to eight.

The report released Thursday focuses on a variation of the third option -- tearing down the section east of Jarvis while maintaining the rest of the road – and its impact on traffic congestion.

It looked at the impact of rerouting traffic along Lake Shore Boulevard, with dedicated turning lanes built to improve traffic flow. It also took into account the time needed for pedestrian crossings, which would be a factor if drivers are forced to find alternatives to the Gardiner.

Researchers also suggested increasing the speed limit on Lake Shore Boulevard from 50 km/h to either 60 or 70 km/h.

The study estimated the change would lead to an increase in commute time of between five and 10 minutes for those travelling east, and four to 6.5 minutes for westbound drivers.

According to the report, 7,500 vehicles travel the eastern Gardiner Expressway each morning rush hour.

On average, those who travel east between Park Lawn Road and the east end of the Gardiner spend 23 minutes on the stretch.

If the city chose to remove the section of the Gardiner and increase the speed limit on Lake Shore to 70 km/h, it would take an average of 27.5 minutes to travel the stretch of roadway, the report found. If the speed limit was increased to 60, it would take 33 minutes on average, an increase of 10 minutes per trip.

A diagram from the University of Toronto report shows the effects of removing the east Gardiner Expressway on daily eastbound commutes:

Gardiner Expressway

Westbound drivers would also feel the effects, although their commutes would not be lengthened as significantly, the report suggested.

Those travelling from the Don Valley Parkway to Park Lawn Road currently spend about 15.5 minutes on the Gardiner. Researchers found that removing the eastern portion would add three minutes to the average commute if the Lake Shore speed limit was 70 km/h.

If the speed limit was 60 km/h, drivers would spend an extra six minutes on their commute.

A diagram from the University of Toronto report shows the effects of removing the east Gardiner Expressway on daily westbound commutes:

Gardiner Expressway