Skip to content
Join our Newsletter
Join our Newsletter

John Ducker: Variable speed limit cuts 'whipsaw'

By keeping traffic flow to a slower but constant speed, the variable speed concept prevents phantom jam ups and improves commute times.
Variable speed limits have been introduced on parts of B.C.'s Coquihalla Highway, John Ducker writes. JONATHAN HAYWARD, THE CANADIAN PRESS

Several years ago I attended a fascinating lecture from the Colorado Highway Patrol. The conference theme was about innovative ways to increase public safety. While most of the presenters talked about drugs, gang crime or preventing youth delinquency, it was the Colorado lecture that stayed with me.

It’s not rocket science to realize that horrendous crashes happen on Colorado highways because of their winter weather. Many areas see snow accumulations of more than 500 centimetres. Thirty centimetres coming down in a few hours during a storm is normal.

This led to an innovative program called “Operation Snow Tortoise.”

It’s pretty simple. A phalanx of snow plows assembles several kilometres out of town on a major route and heads in, clearing the way. Behind them, however, is a wall of highway patrol cars blocking the entire freeway, moving at about 40 to 50 km/h.

This idea worked. Initially, there were zero crashes during morning commutes into Denver. Overall, crashes during storms were reduced by 50% when “Snow Tortoise” was put in effect.

I recalled this effort after I was shown an article about the pros and cons of variable speed limits and how they can actually reduce traffic congestion and crashes.

Numerous studies show that a major cause of highway congestion is the “whipsaw” effect caused when vehicles, moving at different speeds, start piling up behind one another, usually because someone has changed lanes rapidly or braked suddenly to avoid the slower car in front.

This action “whipsaws” back down the line until everyone is moving at a crawl. We’ve all been there. You expected to find a crash or obstruction after inching along at 20 km/h, but discover there was nothing there.

By keeping traffic flow to a slower but constant speed, the variable speed concept prevents phantom jam ups and improves commute times.

B.C. has put this concept in place, but only on the Sea to Sky highway, parts of the Coquihalla and parts of Highway 1 west of Revelstoke.

They were no doubt established because of the extreme road and weather in those areas and it makes sense.

There are two important keys to success with variable speed limits though: put them in the right places and properly educate drivers about what to do with them.

So will we try the variable speed idea elsewhere as they have in Europe and the U.K.? In the short term, not likely.

The technology is expensive and requires constant monitoring to ensure all components of the system work.

Enforcement is tricky during times when the limits change. It requires an extra layer of ­certainty that a limit was in effect and visible at a specific time.

Public acceptance is also a concern. Until motorists are sufficiently educated, there will be misunderstandings about whether a variable speed sign is simply an advisory notice or a regulatory and enforceable traffic control device.

Studies show that the North American driver responds much better to a variable limit if there is a reason to do it, such as the onset of bad weather or being independently aware that congestion ahead is likely.

With traffic flows increasing everywhere as COVID-bound commuters return to the road, the idea of variable speed limit corridors, particularly on already crowded routes, is still an idea worth pursuing.

Glove Box: Still lots of input about traffic circles from readers this week. I said I’d follow up with some info on smaller traffic circles found in residential areas.

Residential traffic circles are basically traffic calming efforts. They should be treated as an uncontrolled intersection — meaning that if two cars arrive at the same time and if you’re not facing a “Yield” sign, then give way to the person on your right. If another car is already in the circle then yield to it.

Always proceed counterclockwise through these smaller circles. You should be making a right turn wherever you exit.

Confusion, though, happens at intersections where authorities have erected the standard triangular yield signs in every direction for drivers approaching a circle, as opposed to the specialized yield sign stating: “Yield to traffic in the circle.”

Four standard yield signs, to my mind, creates a conflict with the Motor Vehicle Act, where section 173 reads: “If 2 vehicles approach or enter an intersection from different highways at approximately the same time and there is a yield sign, the driver of a vehicle facing the sign must yield the right of way to all other traffic.”

Who yields to whom when everyone has a yield sign?

My advice is to treat that with the four-way stop procedure. Give way to the person on your right. When in doubt, make sure you gain eye contact with the other driver and with hand movements either wave the other driver through or thank them for allowing you to proceed.