How and when do officials decide to close B.C. highways?

On Thursday night, every major highway linking B.C.'s Lower Mainland to the rest of the province was shut down dueto treacherous winter conditions.

The Coquihalla was first closedaround noon PT. It reopened at 4 p.m., only to be closed again two hours later.

It would remain closed until 2 p.m. PT on Friday. Hundreds of cars werestuck on the roadway overnight.

Mike Lorimer, the Ministry of Highways regional director for the southern Interior, said the decision to reopen was made because the weather forecast only called for some seasonal snow and a drizzle not treacherous freezing rain.

On Friday, he explained how the choice to close roadways is made.

What makes a highwayunpassable?

Lorimer said "it's very rare" for a highway to be closed "proactively," or before an accident has happened he said most closures happen after the fact.

However, he said there are circumstances that lead to pre-emptive shutdowns.

"We have to have a situation that either our [snow]plows can't keep up with, or there's a hazard that just can't be dealt with through normal adjustments of driving behaviour [such as slowing down]," Lorimer said.

"Obviously, in the case where something specific closes the highway like a vehicle incident or a slide that's an easy decision. When you're making that proactive decision ... there's a lot of thought that goes into it."

Who makes the decisions?

Lorimer said the choiceto close a roadultimately lies with the ministry's district managers.

In B.C., there are 11 such managers each of whomis responsible for a specific section of highways.

They make decisions based on the forecast and reports from staff in the field, Lorimer said.

"[Managers are] out there watching the storm, watching maintenance contractor performance, watching webcams ... you basically look at all the information available and go from there," he said.

Informing driverson the road

Once the decision to close has been made, Lorimeralerts and social media posts are pushed out. The ministry's website is also updated.

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The problem is, Lorimer noted, is reaching drivers who don't have passengers to check conditions onlineon their behalf.

"We don't want to encourage distracted driving," he said.

Lorimer said the ministry is working on improving roadside neon signs.The goal is to haveboards set up strategicallyso drivers will see them before they drive too far into a blocked area.

"We want to give people the chance to turn back," he said.

When are highways reopened?

As for reopening, Lorimer said that"really depends" on the reason for the initial closure.

"Basically, the only rule to reopening is whether or not it's safe," he said. "There is no hard-and-fast rule."

Once highways are deemed safe, Lorimer said the ministry calls for a staggered opening.First, cars that have been waiting like the ones who sat overnight on the Coquihalla will be allowed forward. Then comes local traffic, followed by the broader public.

Ironically, the manager said the rush of new traffic can often cause more problems.

"It's human nature: you've been stuck and delayed and you want to be somewhere," Lorimer said."So, we sometimes see speeding or aggressive driving that can lead to further incidents."

After the Coquihalla reopened Friday, a speed limit of 80 km/h was in place to prevent such accidents.

With files from CBC's Farrah Merali