Toronto will narrow many of the city's traffic lanes in a bid to increase safety by reining in speeds while freeing up space for bicycle lanes or wider sidewalks.

The city has just finished a new policy for lane widths, guidelines that will be rolled out gradually across Toronto.

It will mean that, over a period of years, the lanes on streets across the city will be redrawn. A city official said current widths can encourage drivers to go faster than necessary. The new lanes will generally range from 3 to 4.3 metres, depending on location.

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"The width of the lane often sends a signal to drivers about how much cushion they have and sort of informs their comfort level about how fast they're willing to go," said Stephen Buckley, general manager of the city's Transportation Services department.

The change comes amid a drumbeat of concern about congestion, and after an election in which traffic problems were at the front of voters' minds. Asked about possible outrage from drivers over a city policy designed to slow them down, Mr. Buckley said adjusting the timing of traffic signal schedules can mitigate the effects.

"Our goal here is to continue to try to maintain [traffic flow] at safe and context-sensitive speeds," he said. "And in the downtown core, do you need to be going 50 [kilometres an hour]? Probably not. If we can keep people moving at 30 K or 40 K, smoothly, they'll be ecstatic [about] that."

The department has come up with a fairly complex process to determine how to use space freed up by lane re-sizing.

In some cases, sidewalks might be widened, a recognition that pedestrian volumes in parts of the city are a substantial form of traffic. In other places, the additional space may be given over to cyclists or a median. If a lot of space is left over, additional parking or left turn lanes might be considered.

"You're basically seeing that every city in the U.S. at this point, in their downtown urban core, they're at 10-foot lanes, which are 3.0-metre lanes," Mr. Buckley noted.

It is difficult to say just how much difference these changes will make. Toronto's lanes have been based on Transportation Association of Canada guidelines – which critics say are outdated – and widths vary substantially.

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The default width for curb lanes will be 3.2 or 4.3 metres, depending on the type of road and whether there is dedicated space for cyclists. Through lanes will be 3 or 3.2 metres, based on the size of the road.

All Toronto lanes will have a range of acceptable widths, and factors such as the presence of transit vehicles or heavy pedestrian activity could vary the size. For example, buses operated by the TTC are up to 2.97 metres wide, including mirrors, and lanes on bus routes are to be a minimum of 3.3 metres wherever possible.

Arterial roads are on a 20-year cycle of resurfacing, which would include repainting the lanes to the new standards. Transportation Services is planning to move more quickly, though, to identify and repaint roads where doing so would increase safety or free up useful space. The department's proposed 2015 budget for lane-painting totals $3.5-million, up from $2.7-million this year. Roads in a few areas were done using the new approach before the policy was finalized, but it is not clear where and when the impact will be more broadly seen.

The city's transportation department has been working on the new policy for nearly a year. The work came to fruition shortly after urban planner and Walkable City author Jeff Speck published an impassioned pitch for narrower lanes.

"When lanes are built too wide, many bad things happen," he wrote in widely shared essay last month for The Atlantic CityLab. "In a sentence: pedestrians are forced to walk further across streets on which cars are moving too fast and bikes don't fit."

Many lanes in Toronto are wider than the 3.03 metres Mr. Speck recommends, but the new guidelines would bring them closer.

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"We can modify the paint pretty easily," Mr. Buckley said. "So if we want to do things where we're trying to squeeze out a little more space on an existing road, scrubbing lines and then putting new lines down is pretty easy to do."

The variable nature of street use means there cannot be one standard width for lanes across a city. The new guidelines include a target for each type of road, as well as maximum and minimum widths.

Factors that might prompt a divergence from the target include parking, cyclist or truck volumes and the character of the neighbourhood. The guidelines stress, though, that the target should be "pursued wherever feasible" and that going to the maximum or minimum allowable widths would require "strong and valid justification."