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Behind-the-Wheel

Why is the highway designed that way?

Highway design

Do you ever wonder why some aspect of the highway you are driving on has been designed that way?

It starts with the Transportation Association of Canada's Geometric Design Guide for Canadian Roads, is supplemented by the Geometric Design Guidelines for B.C. Roads, may require compromise due to local conditions and ends up being what you see through your windshield.

I received this:

Some time ago, I wrote to the engineer in charge about the speed limit of 90 km/h at intersections with traffic signals on the Inland Island Highway.

I requested an explanation of the limit at these intersections and also why the 90 km/h limit was placed so far away from the intersection. Not only do most motorists ignore the limit at the intersection, I would guess that (all) ignore the limit where the signs are posted. I never received an answer.

The police have advised me it is necessary to slow to 90 km/h at the sign, although there seems to be no logical reason to do so.

I have often thought that it must be a real challenge to be responsible for highway design here in B.C. Not only do you have mountains and rivers to span—hopefully within budget—you also have to contend with the behaviour of the people who drive on them.

In examining my own perceptions, I often think some things are not logical too.

Most often, if I try hard enough, I can find out the answers but sometimes not. However, it can be dangerous to disregard something that has been carefully planned by professionals based only on your own assessment of logic.

The short answer I have received in the past is something along the lines of "design practices call for it to be done that way."

I imagine that is the polite way of saying they probably couldn't distill a university degree and years of experience into a 10 minute conversation in a way I would understand enough to see the point.

Unless research shows a better way, this is probably the safest approach because we know the outcome.

One example from my collision analysis training might be a vertical view obstruction. The highway looks nice and straight, but a dip in the road can hide a small car entering or exiting at a side road or driveway completely.

The posted speed might be 70 km/h even though 90 k/h looks fine. But 70 km/h is needed in order to perceive and come to a stop in time if something should be hidden in that dip.

That might not seem logical until you understand what is involved.

I can't provide a definitive answer to the question, but I would encourage you to learn more on your own.

The Internet can be a wealth of information, both in web publications and the ability to communicate with knowledgeable people who will take the time to answer.

Don't be discouraged because some engineer failed to answer, rather, consider it a challenge.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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About the Author

Tim Schewe is a retired constable with many years of traffic law enforcement experience. He has been writing his column for most of the 20 years of his service in the RCMP.

The column was 'The Beat Goes On' in Fort St. John, 'Traffic Tips' in the South Okanagan and now 'Behind the Wheel' on Vancouver Island and here on Castanet.net.

Schewe retired from the force in January of 2006, but the column has become a habit, and continues.

To comment, please email

To learn more, visit DriveSmartBC



The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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