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MYTH #6: It's just a holiday traffic problem.

False. It is a design problem that causes congestion and gridlock several times a day.

What causes Congestion and when does Congestion become Gridlock?

Rule 1: Capacity on the open road is not too much of a problem. As traffic slows down the spacing decreases so that more vehicles still get past any given spot.

Rule 2: When the traffic speed drops below 35kph the gain from decreased spacing gets less and less vehicles get past the given spot. Suddenly everything grinds to a crawl. This is Congestion. This is a regular occurrence on all legs of the Hill St Intersection.

Rule 3: If congestion backs up past up to another intersection or constriction that too gets blocked to the point where vehicles cannot move forward and come to a halt. This is Gridlock. Examples of Gridlock.

  • When Elizabeth Street backs up pass the Bridge Hotel it blocks Queen Street/Mill Lane and traffic can hardly move in the whole of the CBD.

  • Similarly if queues on SH1 northbound back up to Shoesmith Bridge through traffic is blocked and this spreads back down SH1, sometimes as far as Puhoi.

  • When someone blocks the intersection at Elizabeth Street by stopping in the ‘clear’ area then nothing happens until traffic at the signals moves forward. Typically this may be a truck and trailer or a bus or a cautious driver. Eventually this clears but by this time congestion has spread back along the approach roads. The Elizabeth Street problem occurs several times every hour. Sometimes this clears in minutes, sometimes it takes hours. Sometimes it blocks back to Sharp Road.

Rule 4: Make sure that queues clear efficiently.

Rule 5: Make sure that you have enough queuing space at all intersections to allow the traffic to clear without backing up to another constriction.

Solve this and you solve the Hill Street Intersection.

Areas of queuing. The Hazard signs are areas of gridlock.

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