new zealand traffic and local air quality

www.elsevier.com/locate/scitotenv

Science of the Total Environment 334–335 (2004) 299–306

New Zealand traffic and local air quality

Paul Irvinga,*, Ian Moncrieff b

aNew Zealand Ministry of Transport, PO Box 3175, Wellington, New ZealandbFuels and Energy Ltd., PO Box 17, Wellington, New Zealand

Accepted 1 April 2004

Abstract

Since 1996 the New Zealand Ministry of Transport (MOT) has been investigating the effects of road transport on local

air quality. The outcome has been the government’s Vehicle Fleet Emissions Control Strategy (VFECS). This is a

programme of measures designed to assist with the improvement in local air quality, and especially in the appropriate

management of transport sector emissions. Key to the VFECS has been the development of tools to assess and predict the

contribution of vehicle emissions to local air pollution, in a given urban situation. Determining how vehicles behave as an

emissions source, and more importantly, how the combined traffic flows contribute to the total emissions within a given

airshed location was an important element of the programme. The actual emissions output of a vehicle is more than that

determined by a certified emission standard, at the point of manufacture. It is the engine technology’s general performance

capability, in conjunction with the local driving conditions, that determines its actual emissions output. As vehicles are a

mobile emissions source, to understand the effect of vehicle technology, it is necessary to work with the average fleet

performance, or ‘‘fleet-weighted average emissions rate’’. This is the unit measure of performance of the general traffic flow

that could be passing through a given road corridor or network, as an average, over time. The flow composition can be

representative of the national fleet population, but also may feature particular vehicle types in a given locality, thereby have

a different emissions ‘signature’. A summary of the range of work that has been completed as part of the VFECS

programme is provided. The NZ Vehicle Fleet Emissions Model and the derived data set available in the NZ Traffic

Emission Rates provide a significant step forward in the consistent analysis of practical, sustainable vehicle emissions policy

and air-quality management in New Zealand.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Vehicle emissions; Pollution; Air quality; New Zealand; Environmental capacity; Policy

1. Introduction

The effects of vehicle traffic on local air quality

have received much attention in New Zealand since

0048-9697/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2004.04.063

* Corresponding author. Now at the New Zealand Ministry

for the Environment, PO Box 10362, Wellington, New Zealand.

Tel.: +64-49177427; fax: +64-49177523.

E-mail address: [email protected].

1996. Routine air-quality monitoring in the main cities

(Auckland and Christchurch) gave rise to concerns

over the level of certain air pollutants commonly

associated with motor vehicle exhaust emissions

(Ministry of Transport, 1998a). At the same time the

New Zealand ‘‘Land Transport Pricing Study’’ (Min-

istry of Transport, 1996) set out to investigate the

social and environmental costs posed by the road

transport sector. However, it was found to be difficult

P. Irving, I. Moncrieff / Science of the Total Environment 334–335 (2004) 299–306300

to quantify the relationships between local air quality

impacts and motor vehicles as an emissions source, to

any meaningful degree.

In response, the Ministry of Transport (MOT)

embarked upon the Vehicle Fleet Emissions Control

Strategy (VFECS) (Ministry of Transport, 1997). This

work programme was designed to give measures to

the ways in which road transport impacts on local air

quality, as a basis for evaluating the appropriate means

for its control. This paper provides a brief overview of

the main issues involved, and the policy outcomes of

the VFECS programme.

Within New Zealand, the general perceptions on

how vehicle emissions affect the environment, and

what should be done about this, were mainly drawn

from observing international experience. The reasons

for, and the success of, these policies have rarely

received critical analysis for local New Zealand ap-

plication. Globally, efforts to regulate vehicle emis-

sions started over 30 years ago, but urban air quality is

still a problem in many countries (Ministry of Trans-

port, 1998b). Recognising the importance of defining

the problem before trying to fit solutions, the VFECS

approach set out with a clean sheet start. The starting

point was to understand the nature and degree of local

air-quality problems in New Zealand, and the critical

component parts in the source-to-impact relationships.

To this end, the following ground rules were set to

ensure the rational and measured approach required:

� Impacts based. The analysis started by defining the

specific nature of the air-quality problem, in terms

of:

– the particular pollutant, and local peak

concentrations;

– by how much these exceed accepted air-quality

targets;

– the contribution from vehicle emissions to this

pollution event.

– This is the basic and legislated foundation of

environmental management in New Zealand,

that it be effects-based.� Quantified targets. As different strategies offer

different emissions reduction effect (at different

marginal cost), there needed to be a clear

consensus on the degree of remediation required,

as the basis for comparing the effectiveness of

management strategies.

� Cost-effectiveness. These targets become the clear

benchmarks for analysing the marginal cost of the

optimum strategies. This was considered more

useful than determining a benefit–cost ratio of

health and environmental gains, where the valua-

tion of benefits had been shown to be less precise.� Sustainability. This placed the analysis in its wider

context, reflecting the ‘capacity’ or limits to

environmental, social and economic effects. It

allowed the basic reason for vehicle use to be

considered, and how the picture might change over

time. This helped to identify the underlying

causes—the demand for travel—and dynamics of

change over time.� Localisation. A spatially structured approach

allowed recognition that local factors can give rise

to a particular airshed problem, that also determine

the optimum means and extent of control to suit the

local circumstances. This also set a basis for

comparing the effect of national level strategies

and those designed around the particular urban

environment.� Practicality. Rather than be reliant on speculative

estimates of performance, it was important to have

confidence that the control measures would actually

work to their potential, in practice. Many policies

can have a high implementation cost and take a long

time to show whether they are working, or not.

The bottom line was to ensure that the process

identified emissions control strategies that are a real fit

to the nature, degree and local specifics of the air-

quality problem—they should address the root cause,

rather than just compensate for its effects.

2. Methodology

The foundation of the VFECS analysis was to set

out a framework for relating the components of a

given area ‘‘emissions loading’’ to the corresponding

air pollution levels in the surrounding airshed. The

critical dimensions in this framework were the con-

sistent definition of:

� Geography. The nature of an air-quality problem is

specific to a locality and the geo-spatial distribu-

tion of the emissions activity.

P. Irving, I. Moncrieff / Science of the Total Environment 334–335 (2004) 299–306 301

� Time. The situation will always be changing,

through short-term emissions activity patterns,

and through long-term change in urban form and

in the evolution of the vehicle fleet.

2.1. Local air quality in New Zealand

The starting point was the understanding of New

Zealand’s local air quality, drawn from the urban

monitoring programmes undertaken by the regional

authorities.

Firstly, the Ministry for the Environment’s ‘‘Am-

bient Air Quality Guidelines’’ were adopted as the

basis for assessing local air quality. Comparing the

monitoring results against these provided the means

for setting targets for improvement, where required.

The results available in 1996 for the main urban

centres (Ministry of Transport, 1998a) indicated the

following results:

� Carbon monoxide (CO) regularly exceeded the

acceptable levels.� Oxides of nitrogen (NOx) concentrations were

approaching the limits in Auckland.� Particulate matter (PM) in Christchurch was a

regular wintertime problem.

These were taken as the main indicator pollutants

for the design of the VFECS programme, as there was

then insufficient information on the ambient levels of

other potential air pollutants, nor had guidelines been

established on their acceptable maximum limits.

The next requirement was to distinguish the prom-

inent emission sources; between motor vehicles and

other combustion activity. This apportionment is a

critical factor in effective air-quality management, if

the correct source is to be managed. However, the

extent to which sources could be clearly defined was

limited by differences in local air-quality monitoring

and emissions inventory practices. The highest levels

for CO and NOx were found in and around the main

arterial road corridors, so these could be attributable to

vehicle traffic. However, the peak levels encountered

could vary significantly with the siting of the moni-

toring point. The PM problem in Christchurch was

significantly the result of domestic fires for home

heating in the winter season (Ministry of Transport,

1997).

A key issue was (and still is) the difficulty in

defining the spatial implications of the measurements

taken at these monitoring sites. Over what area does

there need to be a reduction in emissions activity? The

spatial dimension has particularly significant implica-

tions for the effective management of the vehicle

traffic source, particularly where local corridor con-

gestion can be the cause of locally high emissions

outputs. It was (and remains) one of the major

determinants of the VFECS approach and outcomes.

What was clear, however, was that the nature and

degree of air pollution, and the relative contribution

from vehicle emissions, varied from city to city. There

could be no one-size-fits-all strategy for the effective

management of local air quality in New Zealand.

2.2. Vehicle traffic as an emissions source

On the source side of the equation it was necessary

to define how the vehicle behaved as an emissions

source, and, more importantly, how vehicle traffic

made its impact, locally?

The global emphasis on managing vehicle emis-

sions has traditionally been through the use of certified

emissions standards, applied to the vehicle at the point

of manufacture to progressively reduce tailpipe emis-

sion rates. Over the years, the general performance

levels have improved dramatically, by this measure, by

orders of magnitude since emission standards were first

introduced (Ministry of Transport, 1998b).

Vehicle traffic flow along a rural highway may

make no discernible impact on the surrounding air

quality. However, the traffic flow along a central

urban street can cause exceedance of local air-quality

guidelines. This provided one answer to the nature of

the approach required to understanding and managing

vehicle traffic as an emissions source.

There is more to the emissions performance of a

vehicle than what is certified through its emissions

standard. At manufacture, this simply determines the

engine technology that gives it a general performance

capability. However, it is the local driving conditions

that determine its actual emissions output. Further-

more, because motor vehicles are mobile, anything

done to improve the emissions performance in general

of vehicles may not necessarily result in an improve-

ment for the local area where an air-quality problem

occurs. To understand the effect of vehicle technolo-

Fig. 2. Fleet average CO emission projections.


gy, it is necessary to work with the average fleet

performance, or ‘‘fleet weighted average emissions

rate’’. This is the unit measure of the general traffic

flow that could be passing through a given road

corridor.

The New Zealand Vehicle Fleet Emissions Model

(VFEM) was developed to derive these measures, and

their projection over time in response to fleet turnover

(Ministry of Transport, 1998e). The primary structure

of the VFEM is not the age or source of the vehicle, or

other such factors conventionally used to characterise

emissions performance. It is the interaction of the

engine technology with road design and traffic driving

conditions. In this, the characterisation process for

emissions measures relates directly to the parameters

used in conventional roading practice and in the

design and management of traffic networks. The

VFEM inputs were calibrated using purpose-designed

vehicle emissions test programmes (Ministry of

Transport, 1998c), using transient drive cycles that

represented these traffic conditions, including defini-

tions of ‘Level of Service’ (LoS). The primary struc-

ture for the emissions factor profiling is summarised

in Fig. 1.

This approach makes it possible to correlate the

emissions performance of vehicles, and their various

engine and fuel technologies, directly with their actual

movement in urban traffic networks. The significance

of this is born out by the example of the fleet average

emissions projection for CO, in the form of the gram/

kilometre emission rate per unit vehicle in the typical

traffic flow, given in Fig. 2.

Fig. 1. VFEM emissio

The CO example illustrates the basic trend for all

emission types. The output per kilometre increases

significantly and exponentially with the degree of

traffic congestion. In this example, under central

urban driving conditions, the emission rate for the

traffic flow increases by a factor of three when the

traffic volume approaches the capacity of the road-

way. There is a significant increment again for the

running period immediately after a cold start, typically

2–3 km, which can represent a significant proportion

of a typical local urban trip.

This projection is based upon the New Zealand

fleet evolving with new entrants to the fleet being

constructed to international emissions standards.

Whether these new vehicles are to Euro 2, 3 or 4, or

ns factor matrix.


even zero emissions vehicles (ZEV) actually makes

little difference to the rate at which the entire fleet’s

average performance improves. The ‘‘dilution effect’’

corresponding to this range of emission standards is

around 1.0 g/km down to 0.1 g/km (or zero), com-

pared with a current fleet average of 10 to 30 g/km

across the driving conditions. This shows that the

effect of vehicle technology measures, aimed at im-

proving the fleet-wide performance, is primarily gov-

erned by the rate of turnover of the fleet. It will take

time for the net effect to make a contribution to what

is essentially a local air-quality problem. Also, as

noted above, any benefits from the new vehicles

may not necessarily end up in the area of need and

can be countered by locally increasing traffic growth,

therefore congestion levels.

In summary, this shows the emissions output of

vehicle traffic is effectively a collective source in the

local airshed and is dependent on more than the

tailpipe performance indicators of individual vehicles.

It is the product of three factors.

� Vehicle technology. This determines the average

‘‘Fleet Performance’’.� Road network density. This determines the amount

of potential traffic activity within a given airshed

area.� Traffic density. The traffic on each road corridor in

the network determines the congestion influence

on actual per-kilometre vehicle emission rates.

The emissions factors produced by the VFEM have

been published in a database reflecting current (and

future) understanding of technology and policy. The

emissions factor database has been made available by

the Ministry of Transport on a CD-ROM programme

(‘‘NZ-Traffic Emissions Rates’’, or NZ-TER) for this

local application. The VFEM makes data projections

for the period 1979–2030.

The management of vehicle emissions must

therefore embrace the management of the traffic

network, as well as vehicle technology. Fig. 2, for

the CO example, illustrates the balance between the

benefits of fleet improvement over 10–15 years,

and counter effect of congestion in actual emission

rates. Increasing congestion is a contemporary prob-

lem with the increasing demand for travel in our

cities.

3. Results

3.1. Environmental capacity

All systems have limits. A term commonly used in

roading practice is the ‘‘capacity’’ of the road network.

Capacity reflects the finite volume of traffic the road

can carry before reaching the congested state. An urban

airshed can absorb only so much emissions loading

before concentrations reach pollution levels of concern,

i.e. its ‘‘capacity’’. An airshed’s capacity is at its lowest

under calm, or stable air conditions (Ministry of Trans-

port, 1997). Hence, the concept of capacity can be used

to represent a limiting benchmark for managing the

emissions activity in a given urban airshed. This allows

the different circumstances of both the road network

and the airshed to be considered concurrently, both now

and as the balances change through the future.

The main outcome of the VFECS programme has

been the concept termed ‘‘Environmental Capacity

Analysis’’ (ECA) (Ministry of Transport, 1999). This

process enables local air-quality managers to quantify

the spatial profiles of current emissions activity, from

vehicles and other sources for each pollutant and then

equate the resulting emissions loading to the current

(time-averaged) measured air-quality levels. This will

indicate where the balance lies, between a given level

of emissions activity and sensitivity of the air shed

towards exceedances of air-quality targets (how near it

is to its ‘‘capacity’’). A more detailed description of

how this approach has been used to address both air

quality and other land transport pollution issues is

provided elsewhere (Irving and Moncrieff, 2003).

In reality, this is just an emissions inventory.

However, it is designed to provide consistency

through the use of a standardised framework that

can be applied to any spatially defined urban area,

so that it defines the actual location of emissions

activity (Ministry of Transport, 1998e). This is im-

portant in the management of emissions, especially for

the vehicle sector. If corridor level pollution peaks are

to be addressed, corridor traffic flow management has

implications for the wider traffic network. If the

concern is at the sub-urban level, local traffic man-

agement will have implications for the urban-wide

traffic network.

The ECA framework is built around the city traffic

network modelling process. This is a routine facility


maintained by every urban management authority.

The emissions factors produced by the VFEM are

designed to be integrated with any traffic model, in a

way that can calculate the vehicle emissions loading

for each link in the network, for the current and future

projected traffic flows.

A local case study was conducted in 1999 in

Christchurch to demonstrate the application of the

ECA process to air-quality management (Ministry of

Transport, 2000).

The road network provides the spatial structure in

this inventory process by allowing direct comparison

of the local emissions outputs from the various

sources in the vicinity, for each pollutant. The degree

of spatial resolution required should ultimately be

decided by the air-quality managers, commensurate

with the spatial level at which air quality is to be

monitored and managed.

Once a dynamic emissions inventory is built for a

given city it can be used as a management tool for on-

going use. Built around the road network/traffic

management process the inventory is automatically

updated with the long-term changes in urban network

form and demand patterns for travel. The structure of

the emissions factor inputs gives a direct calculation

of the likely effects of traffic congestion. As we can

see from Fig. 2, it is congestion levels that can be a

critical influence in the sensitivity of the local airshed

towards pollution events caused by traffic emissions.

An illustration of the potential output is given in

Fig. 3, this being of a case-study area within the city

of Christchurch (Ministry of Transport, 2000). This is

based upon a particular micro-simulation traffic model

and displays the relative CO emissions loadings for

vehicle traffic (dark green) and non-vehicles (light

green), for a period of activity between 7 and 8 a.m.

on a winter’s day (the predominant non-vehicle emis-

sions source being domestic fires, in this locality and

time). This particular traffic model can represent

traffic movement on-screen, and the emissions load-

ing calculation is updated second by second, as the

vehicles move through the network.

Such micro-scale modelling may not always be

necessary; the same conceptual process can be applied

to much simpler, spreadsheet-based traffic models, in

which the various links in the network are assigned to a

spatial base. The degree of spatial resolution required

should ultimately be decided by the air-quality manag-

ers, commensurate with the spatial level at which air

quality is to be monitored and managed, subject to the

ability of detail with the local traffic model.

As a dynamic emissions inventory, once built for a

given urban area, it is established as a management

tool for on-going use. Being built around the road

network/traffic management process, it is automati-

cally updated with the long-term changes in urban

network form and demand patterns for travel. The

structure of the emissions factor inputs gives a direct

measure of the effects of traffic congestion, this being

a critical influence in the sensitivity of the local

airshed towards pollution events caused by traffic

emissions.

The main purpose of the environmental capacity

concept is to provide a common basis for dialogue

between air-quality and traffic managers in under-

standing the consequences of changing traffic pat-

terns. It also provides a consistent time and space

basis for comparing the effects of other non-vehicle

emissions sources, and their contribution to pollution

events.

3.2. VFECS policy outcomes

The primary objective of VFECS was to ensure

that the right solutions are employed, to suit the nature

of the air-quality problems. The greater part of New

Zealand does not experience air-quality problems. So

the VFECS policy recommendations were designed to

target the improvement where it was needed and not

impose costs on the rest of the country by requiring

similar standards where it was not. National and local

policy initiatives were developed (Ministry of Trans-

port, 1998d and 1999).

At the national level a number of policy measures

were prescribed to ensure that fleet-wide perfor-

mance improved over time in line with global auto

technology developments. These mainly concerned

the formalisation of new vehicle emissions standards,

the review of fuel specifications to ensure they

would be compatible with current and prospective

engine technologies, and a review for consistency in

local air-quality assessment and management. Other

policy initiatives involved the targeting of excessive-

ly smoky vehicles, and identifying ways to ensure

the vehicle servicing industry would continue to

improve its skill base, to support the appropriate

Fig. 3. Christchurch ECA demonstration example calculation and display.


maintenance of modern vehicle technologies coming

into the New Zealand fleet.

The local urban authorities carry the legislated

responsibility for air-quality management in their

region. The ECA concept enables them to identify

where extra controls may be needed to manage their

local circumstances, which includes how the ‘‘capac-

ity balances’’ are influenced by the local meteorolog-

ical conditions. The process also allows for the

analysis of ‘‘new’’ pollutants as they become identi-

fied. Recently emerging examples are benzene, PM2.5

and PAH, with air-quality data becoming available

that suggests ambient levels of concern. Once the air-

quality targets are set, the ECA process can quantify

the current sources in a given locality, and how the

balances may change over time through natural devel-

opments or in answer to specific mitigation strategies.

Through the future, the ambition is not just to

prevent pollution events from occurring, but to

improve air quality as far as possible. The air-quality

managers can set their targets for improvement, then

analyse through the corresponding emissions loading

benchmarks the incremental reductions required to

attain the targets. The ECA facility provides the

integrated framework for marginal cost analysis, for

the various measures available, against the time

dynamics of fleet turnover and changes to urban

form.

3.3. Health effects and costs of air pollution

More recently, international evidence on the pub-

lic health effects of many air pollutants has become

available. The results of a World Health Organization


study (Kunzli et al., 2000) identifying the health

effects and costs related to the traffic source of

particulate matter in European countries initiated

similar research in New Zealand. Fisher et al.

(2002), in a very preliminary study, reported rates

of premature mortality for New Zealand similar to

those found in Europe. In response, the New Zealand

government is supporting New Zealand-specific de-

tailed research into the public health costs of air

pollution. The results of this research, due in 2005,

will assist in refining future ambient air-quality

targets and policy, and further vehicle fleet emissions

control policy.

The Ministry of Transport is also continually

reviewing global vehicle emissions measures and their

effectiveness, to determine the appropriate New Zea-

land policy response where further interventions may

be required. Recent proposals include nationwide

education programmes focussing on the emissions

performance benefits of vehicle maintenance, and

emissions screening of vehicles both prior to registra-

tion in New Zealand and in-service.

4. Conclusion

This is a summary of a broad ranging programme

of research, analysis and policy work, with many

components involved, that has extended over 7 years

and continues to into the future. Detailed reports are

available from the New Zealand Ministry of Trans-

port. All reports are published on the Ministry’s

website (www.transport.govt.nz). These are recom-

mended for readers wishing to understand the full

context and details implicit in the VFECS and subse-

quent programmes.

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http://www.transport.govt.nz

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