Retaining the eastern part of the Gardiner as an elevated expressway, using the "hybrid option" put forward for the aging thoroughfare during the recent Toronto mayoral campaign, will cost more than $900-million, The Globe and Mail has learned.

An environmental assessment, led by city staff and Waterfront Toronto, that details the long-term costs of the proposal will be released Wednesday. City staff will use it to craft a report that will recommend the best approach for the Gardiner, east of Jarvis. The report is expected by next month, putting the thorny issue in front of city council.

Two sources say the environmental assessment will show that this hybrid option, originally intended to reroute the highway between Jarvis and the Don Valley Parkway, would cost just over $900-million for capital and long-term operating and maintenance costs. This figure is close to double the overall cost of the other main option, removing the Gardiner East and replacing it with a boulevard, which would allow more development but would slow some drivers.

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The hybrid solution came after years of divisive debate about whether to tear down or replace the aging stretch of road. The idea gained broad support among the leading mayoral candidates, but there were few details about how it would work or how much it would cost. The report due out Wednesday seeks to answer some of those questions.

The issue promises to be a delicate one for Mayor John Tory. On the campaign trail and in office, he has presented himself as both a sound fiscal manager and as a champion of drivers. He will now have to weigh how much he is willing to spend to speed up commuters.

The price difference between the two Gardiner East options is less stark when measured in terms of what's known as net present value. Using this approach, removing the section of the expressway would cost about $240-million. The hybrid option would be in the range of 50 per cent higher.

Councillor Gord Perks, who said he couldn't comment in detail on the environmental assessment without having seen it, was skeptical of pouring money into the Gardiner. "Putting hundreds of millions of dollars in premium into something that is based on current levels of automobile use is a bad investment."

What to do about the Gardiner East has been hanging over council for years.

The 1.7-kilometre stretch of road in question is used relatively lightly because it was designed with the assumption that the Scarborough Expressway, which never materialized, would be built. It carries about 5,700 vehicles per hour, in both directions, during the morning rush.

The highway is nearing the end of its lifespan and neither maintaining it nor replacing it in its current form will allow the development of a key site that is needed to help pay for Mr. Tory's transit plans. The only options that allow the site to develop, and the transit funding to flow, are to remove the elevated expressway east of Jarvis or rebuild it and change parts of it.

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A city report last year recommended removing the Gardiner East as the best and cheapest option. But at the time, that option was thought to mean delays of up to 10 minutes for some drivers. Amid push-back, politicians cast about for another solution.

The developers First Gulf presented the hybrid as a way to open up access to their Unilever property, near where the Gardiner and DVP meet. The option would also minimize driver delays by maintaining an elevated and high-speed connection between the highways.

Waterfront Toronto and city staff were tasked with studying that option and in addition seeing what could be done to reduce the travel delays associated with the remove option, which would also open up the Unilever site. According to people familiar with the pending report, replacing the Gardiner East with a boulevard will mean less delay for drivers than was originally thought. But the hybrid option will still be faster for drivers.

The environmental assessment results are expected also to show that the hybrid option has evolved into something that looks very similar to the current highway. Rerouting it close to the rail corridor, as originally planned, proved difficult because it meant curves too sharp to allow for highway speeds.

Instead, the replacement highway would follow roughly the current route. Some ramps will be modified near the Unilever site, allowing development there. But a parcel of land that would be opened up to development by the removal option or by the original hybrid proposal will remain enclosed by elevated highway and the rail lines.