Raising the speed limit on the Whitemud makes sense if the design supports the speed. Mandel's opinion is irrelevant. http://t.co/OArjeDb9dG
— Ryan Batty (@ryan_batty) August 17, 2013
In light of Mayor Mandel’s comments this afternoon referring to the Transportation Department as a “dictator,” I thought it might be worthwhile to expand a little on my thoughts from Saturday.
The issue, for those who don’t know, is that the mayor would like to see the speed limit on Whitemud Drive raised, and based on a report which was prepared for Council, the Transportation Department is saying that the current limit of 80km/hr is appropriate. I’ve neither seen the report, nor had anything to do with any projects on the Whitemud so I have no specific information, but I’ve got a couple of ideas about what the problem might be.
The first is consistency. Ideally, the posted speed limit along a roadway wouldn’t change as you drive from one end to the other. A consistent speed limit provides the driver with a certain expectation, and avoids situations where a driver misses a speed limit change creating a potentially unsafe situation by travelling to fast or too slow for a particular section of road.
Speed limits are usually based on the characteristics of the roadway, including the horizontal and vertical geometry, lane widths, and intersection or interchange spacing. The problem with a consistent speed limit is that you end up posting the speed based on the lowest design segment of the roadway. In the case of the Whitemud, if I had to guess, I would say this is the section around Terwillegar Drive. where there are two relatively closely spaced interchanges, the interchange at Terwillegar Drive has a non-standard design with left-hand entrances/exits, and there is a 90 degree curve in the roadway alignment.
I don’t know for sure, but I suspect that other sections of Whitemud Drive, if looked at in isolation, would be able to safely accommodate a posted speed higher than 80km/hr. And that’s the rub, because a speed limit should not only be consistent but also credible. If the east and west ends could be safely driven, based on the chosen criteria, at say 100km/hr, then a choice needs to be made between consistent and credible. So, in a way both the mayor and the Transportation Department are sort of right in this situation.
But there is a second issue that might be playing a factor here, and that is the actual travel speed. I know I’ve heard the rumour that anything the police use to measure your speed has limited accuracy, and that you can’t get a ticket if you’re not going more than 10km/hr over the speed limit. I’ve never gotten a speeding ticket so this might be true, but it seems suspect to me.
That people speed isn’t automatically a problem though since most roads are not designed to be driven at the speed they are posted at; often times the difference is 10km/hr. Think of it as a factor of safety for the driver. But if people believe they are “allowed” to drive 10km/hr over the speed limit and the travel speeds are already approaching the safe design limit, then increasing the posted speed might result in an increased number of collisions. And I think we can all agree that would be undesirable.
So what do you do? You could raise the posted limit and increase enforcement, but I doubt that would be very popular even if it’s done in the name of safety. Or just leave it the way it is, which is also going to be unpopular. I don’t know the answer, but I’d be willing to bet this isn’t the last we’re going to hear about it.