Friday 13 March 2015

Myths & Reality #1

I'm going to start a little series on "Myths & Reality"

It's quite common to see these from a pro-PT anti-road point of view but I'm going to try and make this series cover both sides.

So to start things off here is Number 1.

"Roads are Designed to Eliminate Peak Hour Congestion and are Empty for the Rest of the Day"


This is a common one from the anti-road brigade and is generally used as an argument against road improvements and motorways as it is claimed they are significantly under utilised for most of the time.

The reality is we can't afford to design roads to eliminate the peak hour traffic congestion, what road designers do is design roads to "manage" peak hour congestion. This may very well mean that the average speed is reduced from 100km/h down to 70km/h but the aim is to keep traffic flowing smoothly and safely.

It is the inter-peak hours that we try and keep traffic flowing at optimal conditions.

The following photo shows the Northern Motorway on a Saturday afternoon. You can see here that there are quite a few cars and if it were a video you would note the traffic was flowing smoothly. It is however in a bit of a fragile state in that one crash could cause some real issues, and when you have 160,000 vehicles a day driving along a given section of road the chance of there being is crash is quite high. Given there are wide shoulders here the traffic impacts of a minor crash would be much less than what we have been seeing on the North-Western Motorway (SH1) where a single crash would bring this level of traffic to a stand still.

Northern Motorway (SH1) Weekend Traffic

The next photo shows the South-Eastern Motorway (SH20) on a Sunday afternoon. You can see here that the road is rather quiet and flowing completely smoothly. A minor crash here would be of little consequence in terms of the of traffic flows. This section of road gets about 70,000 vehicles a day and potentially you could question as to why it was recently upgraded from 2-lanes each way to 3-lanes each way. The simple answer to that is forward planning as in 2017 the Waterview Tunnel is expected to open which will result in another 60,000 vehicles driving this route every day.


South-Western Motorway (SH20) Weekend Traffic
So what does any of this have to do with designing roads to handle peak hour congestion?

Well basically these photos are showing the motorway operating in near optimal conditions. The Northern Motorway is a little too close to capacity and the South-Western is a quite a bit under.

When it comes to peak hour when there is two or three times more traffic however, the northern motorway will be in stop start condition and the south-western will be close to flow breakdown. In both cases one minor crash would result in significant delays.

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