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The Gauntlet: Issue #15

Newsletter #15 - 29 December 2016

We hope that you all had an enjoyable and memorable Christmas. Our teams had the initiative to be out on Boxing Day collecting signatures for our petition at the Hill Street intersection. Thank you to those who signed it.

Over the past and coming week, the NZTA control centre are watching the traffic at the Hill Street intersection and configuring their traffic light sequences to minimise queues. That’s no holiday.


Your guess is as good as mine… and the NZTA’s.

We’ve been comparing the NZTA’s forecasting with real-time data. There is a real disparity between previous year’s peak flows and this year’s. How can this be?

Take for example Tuesday, which NZTA forecast to have the longest peak period of 8:30am-6:30pm. Consensus is that congestion on Wednesday and Thursday has been worse.

There are three things to take into account:

1. The circulation of forecasted traffic information;

2. The reaction to that information; and

3. The desired response to the information.

The NZTA warned motorists to expect delays and heavy traffic volumes on their website, Facebook page, and Twitter feeds. They also alerted the mainstream media. At motorway electronic noticeboards as south as Greenlane, they recommended that northbound traffic use State Highway 16 to Wellsford and avoid State Highway 1 through Warkworth.

It was the NZTA's largest congestion warning ever. But who listened?

Take for example the period before Christmas. Warned about congestion, many left early – often finding that others had the same idea (

Central to congestion problems is a lot of people having the same idea of jumping into their cars and going to the same place. When warned by a forecast that the congestion or weather will be bad, many might change their schedule to another time – and many others might have the same idea. If the alternative journey window narrows, congestion could be worse than what motorists were trying to avoid.

Holiday traffic patterns are predictable. Christmas shopping, Christmas gatherings, and New Year’s gatherings are different in subtle ways. Many celebrate Christmas and New Years in the same place. Some migrate from family gatherings to social outings on the coast. Some sneak in a week of work in between.

In between Christmas and New Years there are only a few days to squeeze in a journey. Rationally, the NZTA would want to spread out the volume of traffic across the widest period. By producing forecasts and traffic warnings, however, rational outcomes don’t often occur.

The problem is that forecasts can appear to be too accurate and people rely on them too much. Seeing that off-peak starts at a certain time, people leave later - and arrive much later due to the unanticipated congestion.

If you look at the “hotspot” chart produced by NZTA, you will notice how there is red in the centre, surrounded by orange and green. Basically, it has many similarities with a “Normal Distribution” model ( The twin peaks of Tuesday and Friday, however, are like a “Bimodal Distribution” (

Normal Distribution Model

The problem with identifying that Tuesday will be the worst day to travel is that it is the day after Boxing Day and many would see that traveling on Wednesday and Thursday looked more favourable. Some Wednesday and Friday travellers might also change to Thursday.

So, what started as two smaller peaks has become a much higher and steeper summit. Effectively, the NZTA has made congestion worse.

Bimodal Distribution Model (Forecasted Traffic Peaks) adapted to Normal Distribution (Actial Traffic Peak)


The NZTA can look back at how motorists reacted to traffic alerts and forecasts. They should gain a better understanding of the different types of motorists, how many of each type there is, and whether they heeded the advice.

We aren't so sure. The toll barrier reads licence plates. Are they using that information to find out which segments of motorist adjusted their behaviour?

Diffusions of Innovations Model

According to the "diffusions of innovations" model (, the rate of adoption of technologies and trends is a normal distribution where laggards are the least likely to respond to the latest information/technology/trends. Alternatively, innovators are more likely to adopt the most recent and best quality information.

So, what is the best information? The best real-time information is Google Maps ( The next most accurate information is social media, then radio reports. Then there is traffic forecasts, mainstream media, followed by a motorist's own past experiences, and, finally, motorists with little or no past experiences travelling the route who don't rely on other sources of information (the "laggards").

Anyone relying on Google Maps would receive accurate information before they jumped in their vehicles. Anyone relying on social media or the radio would rely less up to date information.

Anyone relying on NZTA forecasts, who then delayed their journey, and then looked at Google Maps and realized that traffic is worse than anticipated could make things worse by delaying their journey further as the window of opportunity narrows.

The best option could have been to rely on Google Maps from the start and traveled on the Tuesday. This would be ignoring NZTA's forecasts but would expect "early and late majority" to follow NZTA's travel warnings and travel on Wednesday and Thursday.

It's like the weather: look at the forecast and then look out the window on the day.


When infrastructure is regularly near capacity, the congestion is more temperamental. Tolls, congestion charging, and forecast warnings are measures used when there are capacity issues.

Infrastructure shouldn’t be built to accommodate the average daily use. It should be designed to accommodate the peak hour use. You don’t build a sewerage scheme to deal with the annual daily average. If 90 percent of people at a resort flush the toilet between 9-10am on New Years’ Day, you design the capacity of your scheme to cater for that.

Unfortunately, the NZTA and Auckland Transport don’t take that approach to the traffic flow at the Hill Street intersection. If you look at NZTA and Auckland Transport data on the Hill Street intersection, it gives little indication of the capacity of the intersection because, basically, they don’t know.

We’ve spent 2016 identifying the problems and looking at solutions. We know that Auckland Transport is now serious about finding a long-term solution. We’ve come up with what we think will fix it. Our challenge for 2017 to NZTA and AT is to better it.

Our New Year’s resolution is make sure that contractors are ready to break ground to fix the Hill Street intersection. With your support, we will do whatever it takes to achieve that goal.

THANK YOU Please contact us if you would like to donate, volunteer, or have any suggestions.

Please contact Alan at (027)2419033 or if you have any time available to help us collect signatures for our petition.

To make a donation, our bank account details are:

Account Name: “FixHillStreetNow Action Group” Bank Account Number: 12-3095-0042062-00.

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