Arterial Traffic Study frequently asked questions

Subject: Funding and timing of the study

What is the overall cost of the study and how is it funded?

The study cost is $355,000.  The New Zealand Transport Agency (NZTA) has agreed to fund 75% of this study from its National Land Transport Fund.  The remaining 25% is funded from NCC rates.

When will each stage of the study be completed and how can I find out about them?

The terms of reference for the study identifies 4 stages with each stage requiring approval by NZTA before it is published and the next stage commenced.  The date each stage is due for publication is identified below:-

Stages of the Arterial Traffic Study



Report release date


Evaluation of existing arterial traffic flows

week 7 June


Selection of best arterial route options

week 7 June


Evaluation of best arterial route options

mid-October (1 Dec: DELAYED)


Determination of preferred option

30 November (1 Dec: DELAYED)

NCC will publish the outcome of each stage on these web pages.

Why is the study not going to be completed before the local body elections?

The study was originally intended to be completed prior to the 2010 local body elections but NZTA funding approval couldn’t be applied for until after the local share was approved in July 2009 following the Community Plan process. NZTA adopted its National Land Transport Fund in August 2009 and final study approval was given in October 2009.

Subject: Modeling

Will the traffic model take into account the planned expansion to public transport identified in the 2009-19 Community Plan for 2012/13?

Yes, the base model, which the final preferred option will be assessed against, is based on

  • the current roading network, and
  • the current roading network with public transport improvements as identified in the RLTS, Appendix 1, for commencement in 2012/13 (as identified in the 2009-19 Community Plan, subject to NZTA funding approval)

How does the traffic model take into account the planned initiatives identified in the 2009 Regional Land Transport Strategy? i.e. an expanded passenger transport network

The Nelson TRACKS Transportation Model replicates the number of trips occurring on the road network for the following modes of transport: vehicle driver, vehicle passenger, public transport (bus), cycling and walking. The cost of travel by one particular mode of transport may change due to a number of factors. These include (but are not limited to):

  • distance and/or time taken to travel from one place to another due to new roading
  • distance and/or time taken to travel from one place to another due to increased or decreased congestion
  • cost of public transport (bus fare)
  • time taken in walking to public transport or waiting for the next service
  • cost of parking in the city centre for motorists
  • road tolls or other charges
  • cost of fuel for motorists

In the modeling process all of these cost components are added together to calculate the cost for any person to travel from one part of the city to any other part as a vehicle driver, vehicle passenger, bus passenger, pedestrian and cyclist (note that these last two active modes are combined in the model). The relative cost of travel by each of these modes is compared within the model and a certain number of trips are allocated to each mode using a set of calibrated mathematical equations. These equations have been formulated to replicate current travel behaviour in Nelson City and the Tasman District and as such an appropriate number of people using each mode is modeled.

When one of the cost components changes, the model is designed to pick this up and reallocate the trips across the modes accordingly, and in doing so replicates what would be a real-world response to changes in the cost of travel. Below are a couple of examples to give the reader some idea of how the model responds (these are just a few relevant examples of the many applications of the Nelson model):

Example One - Change in the cost of parking pricing

The Nelson model includes a comprehensive parking module which knows the number of, location of, any time restrictions and price of parking throughout the central city. If parking prices in the CBD increased then those vehicle driver trips which travel to the CBD parking zones would become more expensive. Subsequently the cost to undertake such trips as a vehicle driver becomes more expensive in relative terms. As such when the model allocates the trips to the various modes of transport, fewer trips would be allocated to the vehicle driver mode as this has become more expensive and the cost of travelling as a vehicle passenger, by bus or by active modes is unchanged.

Example Two -Increase in Petrol Prices

As petrol prices increase the cost to drive around the city increases. The perceived cost to vehicle drivers is a function of the vehicle operating costs (in cents per kilometre) and travel time (in cents per minute) plus any additional fixed costs such as parking and tolls (where applicable). If petrol prices increase by 50% then the cost to travel the network in cents per kilometre increases markedly and as such trips as a vehicle driver becomes more expensive in relative terms. When the model allocates the trips to the various modes of transport, fewer trips would be allocated to the vehicle driver mode as this has become more expensive and the cost of travelling as a vehicle passenger, by bus or by active modes is unchanged.

Example Three -More Public Transport Services

When new bus routes are established the cost to access the nearest bus service (usually by walking to the nearest stop) becomes significantly less for persons living, working or going to school in the vicinity. Rather than walking a number of blocks which may take 15-20 minutes, a handy service on a new route 5 minutes walk away saves the public transport user time. The cost to use public transport in the model takes into account the walk (or access) time and as such the cost to use the bus service reduces. When the model allocates the trips to the various modes of transport, more trips would be allocated to public transport in this vicinity as this has become less expensive and the cost of travelling as a vehicle passenger, by bus or by active modes remains unchanged. By the same rationale if existing bus services are more regular the bus user is likely to face less waiting time for a service, therefore the cost to use buses are cheaper and the model allocates more trips to buses. If bus fares decrease the same occurs. If bus priority measures are built into the model, the time taken to deliver passengers to their destination decreases and the model allocates more trips to buses again.

The model also understand the level of trip making potential of different areas (referred to as model zones) within Nelson City and Tasman Region as it knows how many households, persons, vehicles, jobs and student enrolments there are in each area. As the number of any of these variables change in any of the approx 500 model zones within Nelson and Tasman, the model picks up this change and modifies the travel demand on the network accordingly. This is included in the model as additional vehicle driver, vehicles passenger, public transport and active trips. In this way it is able to account for new residential and commercial activity in the future, allowing NCC and TDC to plan the road network and public transport services so that it can cope with future demands.

Will the traffic model take into account the increasing proportion of elderly living in Nelson?

The age and demographic functionality within the model is limited to two factors

  • the average number of persons in each household and
  • the number of vehicles per household

The first of these variables loosely encapsulates the aging population issue but does not isolate retired persons as a 'lifestyle' category. The second variable can be to some extent a function of household size but is also a socio-economic parameter with more affluent areas having a higher car ownership.

On what basis does the model account for future population growth?

Council’s population growth figures are based on Statistics NZ Census and projected population growth figures, and are adjusted to take account of local changes.  Planning in the arterial traffic study is based on a base population of 44,300 as at the 2006 Census.  In summary, it is estimated that Nelson’s population will increase as follows:-

  • 2006 – 44,300
  • 2016 – 47,185
  • 2026 – 50,302
  • 2036 – 51,937

Based on a falling rate of people per household (2.56 in 2006 to 2.25 in 2031 suggested by Stats NZ) the additional number of households anticipated each year is 230.

This is a lower rate of increase than was assumed six years ago when the first Nelson to Brightwater model was developed.  At this time it was estimated that 11,668 new residents by 2021 would need up to 6,223 new houses, units or apartments.  Estimates have been revised downwards due to declining net immigration and other factors represented in the latest census figures.

What energy price is the traffic model based on?  How will the potential effects of “Peak Oil” and oil price rises be taken into account in the study?

The 2006 traffic model is based on the vehicle operating costs specified in the NZ Transport Agency’s Economic Evaluation Manual.  The effects of future oil price changes will be assessed by undertaking additional model runs varying the cost of fuel.

From traffic data published in the 2009 Regional Transport Strategy it appeared that the opening of the Whakatu By-pass induced more traffic onto the roading network.  Will this induced traffic potential be accounted for in the modeling for any new roads that are considered as part of this study?

The model works from first principles to determine trip generation, trip attraction and modal split from land use and network data.  Accordingly, if a new road was to be constructed, the model would determine if additional trips would be created as a result.