The Role of the Highways Agency in Local Air Quality Management, January 2005

Contents

  1. Introduction
  2. The Highways Agency's Role
  3. What Effect Would it Have on Air Quality?

References and Annex

The Role of the Highways Agency in Local Air Quality Management, January 2005

1. Introduction

1.1 Purpose of this Document

The Highways Agency (HA) is the network operator for England's network of trunk roads, including motorways. Whilst this network represents only a small proportion of the national road estate it has a far greater significance in terms of the extent to which it is used. Over 30% of all traffic is carried on the HA network and the proportion of HGV traffic is nearer 70% (by vehicle miles). Carrying such large volumes of traffic means that in areas near to busy trunk roads air quality is likely to be significantly influenced by vehicle emissions.

The need to consider air quality issues is however not something new to the HA and for several years the HA has been gaining expertise and experience in the assessment of air quality impacts and measures that may contribute to their reduction. Identified as a statutory consultee through the Environment Act 1995, the HA is committed to working in partnership with local authorities towards the delivery of the Air Quality Strategy (AQS). The objective of this document is to provide our partners with a guide to engaging with the HA. The document has three main purposes:

1.2 Introducing the Highways Agency

Whilst the HA is well known to many local authorities there are many for whom contact prior to the AQS has been limited. Established in 1994, the HA is an executive agency of the Department for Transport (DfT). The Secretary of State is responsible for overall Government policy on motorways and trunk roads in England and determining the strategic framework and the financial resources within which it operates.

1.2.1 What does the HA do?

The HA maintains, operates and improves the network of trunk roads and motorways in England on behalf of the Secretary of State for Transport. The Agency currently manages and maintains a network of some 8,255 km of motorways and trunk roads in England.

Our aim is "Safe Roads, Reliable Journeys, Informed Travellers".

We have five key objectives:

  1. To deliver a high quality service to all our customers by:
  1. To ensure more effective delivery through better working relationships
  2. To implement best practice and innovative solutions to improve service now and in the future.
  3. To be a good employer.
  4. To be an efficient Agency with effective business processes and resource management systems.

Introducing the Highways Agency

1.2.2 Engaging the HA in Air Quality Management

The HA operates from seven regional offices with a small headquarters office in London. Each region is divided into areas containing a number of trunk road routes. To each is allocated a dedicated team and each route within an area has a route manager. In the first instance all contact with the HA on local air quality management issues should be with the relevant route manager.

The Agency's areas are shown on the map and are broadly summarized to the side. Please note that some counties appear in several Agency areas but the map shows which roads are included in each area.

Agency Areas

Broad Description

  1. Cornwall and Devon
  2. Somerset, Avon, Wiltshire, Gloucestershire and Oxfordshire
  3. Hampshire, Surrey, Berkshire, Oxfordshire, Dorset and Wiltshire
  4. Kent, Surrey, East and West Sussex
  5. Berkshire, Buckinghamshire, Essex, Hertfordshire, Kent and Surrey (M25 sphere including associated link roads, stubs and tails in London)
  6. Hertfordshire, Essex, Cambridgeshire, Suffolk and Norfolk
  7. Leicestershire, Lincolnshire, Nottinghamshire and Derbyshire
  8. Buckinghamshire, Hertfordshire, Bedfordshire, Essex, Cambridgeshire and Northamptonshire, Oxfordshire and Leicestershire
  9. West Midlands, Herefordshire, Worcestershire, Shropshire and part of Warwickshire
  10. Cheshire, Greater Manchester, Merseyside and the Wirrel
  11. Warwickshire, Leicestershire and Staffordshire
  12. Yorkshire and Humberside
  13. Cumbria and parts of Lancashire
  14. Northumberland, Tyne and Wear, Durham and North Yorkshire

The individual Agency areas can be seen here. The route manager can be identified by selecting which Area the road is in and emailing odareax@highways.gsi.gov.uk where x is the area number (for example odarea1@highways.gsi.gov.uk) and stating which road you are interested in and that you would like to contact the route manager.

The HA can also be contacted by telephone - the National Switchboard number is 08459 55 65 75 and the Information Line number is 0300 123 5000.

To advise our route managers the HA also has specialist technical staff. The Environmental Policy group is responsible for the provision of technical advice including the air quality section within the Design Manual for Roads and Bridges (DMRB) Volume 11, Part 3, Section1. This group also supports a number of air quality research projects and the HA's network of long term roadside air quality monitoring sites.

1. Introduction

2. The Highways Agency's Role

Our purpose is to operate, maintain and improve the strategic trunk road network with one of our objectives being to respect the environment. We can influence our effect on air quality through:

Our plans for the network are discussed below together with how these could affect air quality. Local authorities will need to be aware of these when assessing air quality and preparing their action plans.

2.1 Strategic Planning

2.1.1 Multi-Modal Studies

In the past, road congestion, safety and environmental problems have been addressed by simply increasing road capacity. There is still a need on occasions to look solely at road based solutions but the purpose of the multi modal studies is to examine the role of all transport modes in the area or corridor concerned to identify the contribution that each can make to solving the problems of the corridor and meeting the objectives for sustainable development.

The multi-modal studies do not look simply at a congested or unsafe stretch of road to decide what improvements could be made, but also examine what scope there may be for expanding public transport or for traffic management measures to manage the demand on the existing infrastructure. A strategic level assessment for air quality according to the Guidance on the Methodology for Multi-Modal Studies (GOMMMS) has generally been carried out as part of these studies for the proposed strategies and for the do-minimum scenario. This involves identifying the change in emissions of NOx and PM10 expected in each zone within the study area for each strategy and relating it to the population within that zone.

After reviewing the multi-modal studies, the Department for Transport makes recommendations as to which schemes should go-ahead. These recommendations are based on the Government's objectives for transport. Some schemes have been turned down on environmental grounds. If a scheme is approved, it will then enter the Targeted Programme of Improvements (see section 2.2.1) and will be subject to rigorous appraisal.

Information on the multi-modal studies is available from the Government Office for each region. The web addresses for each Government Office are given below:

South-east (http://www.go-se.gov.uk)
Eastern England (http://www.go-east.gov.uk)
East Midlands (http://www.goem.gov.uk/)
South West (http://www.gosw.gov.uk)
North West (http://www.gonw.gov.uk/)
North-east (http://www.go-ne.gov.uk)

The map below indicates the areas that have been addressed in the multi-modal studies.

The map below indicates the areas that have been addressed in the multi-modal studies.

2.1.2 Managing Demand

It is widely accepted that it will not be possible to build our way out of the increasing pressure on road space. The Department for Transport has published a discussion paper "Managing our Roads" to stimulate discussion around the key themes of tackling congestion and managing demand for road space. It considers how demand for road travel might increase into the future, what measures might be taken to reduce the need for car travel, how to make best use of the existing network and the choices to be made to balance the issues of capacity and demand. The document can be viewed at http://www.dft.gov.uk/stellent/groups/dft_transstrat/documents/page/dft_transstrat_022865.hcsp.

The Department for Transport has commissioned a feasibility study to look at the practicalities of road user charging to reduce demand. There are a number of issues that need to be addressed such as protection of privacy and whether any scheme could work technically. Road user charging was part of the strategy in some of the multi-modal studies.

2.1.3 Route Management Strategies

Route Management Strategies (RMS) are about making better use of the existing roads. The process has been developed to help the HA to focus on local needs, consider how to integrate roads planning with other transport and planning decisions in addition to looking at the regional picture. This is done by taking a strategic approach to the maintenance, operation and improvement of its network, and involving regional stakeholders and the public in the decision-making process. Each RMS will lead to the adoption of a ten-year strategy and a three-year investment plan for each of the routes comprising the strategic road network. It is the intention that every route in the strategic road network has a RMS in place by March 2004.

The main features of a RMS are:

As an example of what can be done through RMS, the RMS for the M5 Junction 21-31 (Weston-Super-Mare to Exeter) recommended

The RMS for the M26/M20/A20 in Kent identified improving air quality as one of 13 high priority actions. It will investigate solutions such as reducing congestion and will consider speed and access control.

The local authority will be notified via a press notice that the HA intends to develop a RMS in their area. Seminars and consultations will be held during the development of the Strategy to enable stakeholders and consultees to express their views. The local authorities should take an active part in the development of these RMS to ensure that appropriate strategies are developed that take account of local conditions and their concerns. If a road is identified as already being at capacity, the RMS would include a land-use planning and development control statement to restrict any development that would increase flows on that road.

2.2 Road Improvements

All of our schemes are subjected to the standard procedures for rigorous appraisal, including an assessment of their impact on air quality, and progression is dependent on the satisfactory completion of statutory procedures.

The air quality assessment would include, as a minimum, an assessment of the overall change in NO2 and PM10 concentrations at properties as described in the DMRB. The larger schemes would require Environmental Statements that would contain an air quality assessment carried out in accordance with the guidance in the DMRB. This would include:

2.2.1 Targeted Programme of Improvements

The Targeted Programme of Improvements (TPI) aims to address some of the most pressing network problems, easing congestion and making travel safer, providing safer and healthier communities and supporting regeneration and integration. The schemes comprise of a number of major schemes each costing more than £5m, funded either conventionally or by public-private partnership.

When announced in 1998 as part of "A New Deal for Trunk Roads in England", the TPI consisted of 37 schemes. Since then further schemes have been added, some of which are due to the outcomes of the multi-modal studies. The schemes included in the programme are listed in Annex 1. Further information on each of these in terms of progress and the Appraisal Summary Table, which includes the expected effect on local air quality, is available at for all the TPI schemes. Local authorities should include these schemes in their review and assessments if they are expected to be operational during the assessment years.

Road Improvements

2.2.2 Junction Improvements

Ninety two junction improvement schemes will be carried out over the next five years to tackle congestion and improve safety at junctions across England's trunk roads and motorways. These schemes will address some major bottlenecks so cutting queues, improving traffic flows leading to more reliable journey times and reduced emissions. Locations where problems have been identified range from major motorway junctions such as junction 10 on the M62 near Warrington, to congested dual-carriageway roundabouts such as the A38 at Derby, to crossroads such as on the A64 at Bramham in Yorkshire.

2.2.3 Local Network Management Schemes

These are small schemes aimed at making better use of the network as it stands. Whilst many of them relate to improving safety, they can also deliver improvements to air quality.

2.3 Integrated Transport and Sustainable Travel

2.3.1 Encouraging Travel Changes

By widening the choice of transport available for the movement of people and goods, rather than relying solely on roads, levels of congestion and pollution could be reduced. The Agency can play its part by helping to develop proposals for passenger and freight interchanges, offering better information about travel choices, and giving priority at specific locations to particular classes of vehicle. Our objective is to work with others to ensure passengers and freight operators can switch efficiently and smoothly between different modes of transport, and to broaden the choices available. It is also important to ensure that our activities reflect Government policy across the whole spectrum to promote safe, healthy and inclusive communities.

Our role is described in more detail.

Actions we can take include:

Examples of where we have done this include:

We have also carried out pilot studies with local authorities and transport operators to develop campaigns to encourage a switch from road to rail. Three campaigns were held to explore the difficulties and benefits of different transport organisations working together.

The A12 Chelmsford to London is an important commuter route where the main rail route to Ipswich closely parallels the trunk road. The campaign, run in partnership with First Great eastern, encouraged a switch to rail at peak times. Six percent of people who recalled receiving the publicity leaflet said that they had changed their travel behaviour as a result. Eleven percent of these caught the train instead of driving with the remainder not driving to the station or making fewer journeys.

The A47 from Norwich to Yarmouth is a route which has the potential to switch both leisure and commuter trips to the parallel rail and high quality bus routes using special ticketing offers promoted by the operators Anglia Railways and First Eastern National. A "kids travel free" offer attracted over 500 users and "two weeks for the price of one" 50 users. The savings from the special offer were the prime motive for the change in behaviour with 20% of those travelling having changed their mode of travel as a result.

The A696/A1 north-west Tyneside to Newcastle is an urban corridor with potential to increase park and ride at two stations on the existing metro. The campaign was conducted in partnership with Nexus and provided a free service. The park and ride utilisation increased significantly during the campaign period and the increase was maintained afterwards.

Further information on these pilot studies.

2.3.2 Encouraging Sustainable Travel

As operator of the nation's strategic roads, we have a responsibility to all of our road users. Whilst most of the business is concerned with providing for the movement of motor vehicles throughout the network, there are also a significant numbers of non-motorised users whose needs must be addressed. These include pedestrians, cyclists and horse riders. Moreover, there is an important role to play in improving access to everyday facilities for those without access to a car - one of the Government's key transport objectives. We must also ensure that the needs of disabled people are met and that, as far as possible, we act both to reduce the severance effect which strategic roads can have on the communities through which they pass, and to improve access to public transport. A Strategic Plan for Accessibility has been prepared that explains how we intend to meet these challenges in the years ahead. However, implementing these plans requires partnership with other organisations.

Actions include:

Examples of where we have done this include:

2.4 Better Information and Improved Operation through Technology

2.4.1 Real-Time Traffic Information

In order to avoid congestion, travellers can currently obtain real-time information on traffic speeds for a number of areas on the motorway network (M25, Kent, Birmingham, Leeds and Manchester) and can then plan their trip accordingly. In addition, the TrafficMap service provides comprehensive information about motorway incidents and what the motorway signs are saying to help plan the journey.

The traffic control centre (TCC), due to open in 2004, will introduce coordinated up-to-the-minute information on the majority of the strategic road network. The information will be available to travellers and organisations such as the police, local highway authorities and other transport operators. The TCC will focus on journeys made on the nationally important parts of the strategic road network. It is planned that the information gathered will be integrated with information collected from other Government initiatives looking at other transport modes (e.g., train, bus, air).

By providing the right information where and when it is needed, the TCC aims to:

2.4.2 Active Traffic Management

The aim of Active Traffic Management is to contribute towards easing congestion, safer travel, better information and smarter roads. Easing congestion should lead to an improvement in air quality for some pollutants.

The benefits provided to the road user will be:

Where appropriate, ATM will incorporate the following features:

ATM is being piloted on the M42 Junction 3A-7 which is the south-eastern quadrant of the M42 around Birmingham. The impact on air quality will be assessed during the pilot study which will commence in 2003.

2.4.3 Message Signs

If drivers are made aware of the location of AQMAs, then they may be willing to modify their activities to reduce emissions. To this end, we are liaising with the DfT and Defra to design a road sign that could be used nationally to advise drivers that they are entering an AQMA. Static signs could also be erected to advise of Park and Ride or other similar facilities in support of initiatives being carried out by local authorities, provided that those facilities meet certain standards.

Variable Message Signs could also be used to advise of poor air quality and encourage drivers to modify their activities. Again, we are liasing with Dft and Defra to identify appropriate messages. Clearly, these messages could only be deployed on routes equipped with Variable Message Signs.

We will be preparing a paper in association with DfT, Defra and the local authorities on the signing strategy.

2.4.4 Traffic Management during High Pollution Episodes

As part of the DfT's TRAMAQ research programme, an assessment was made of the feasibility of using traffic management measures during high pollution episodes to improve air quality (UG212). High pollution episodes tend to be caused by specific meteorological conditions rather than increased emissions and are an infrequent event. The measures considered were wide-area access control, parking charging / restriction, influencing key traffic generators, voluntary restraint and urban traffic control systems. Forecasts of these events would need to be given 1 to 3 days before the event to enable people to modify their normal travel patterns. It was considered that there was relatively good infrastructure already in place for the dissemination of this information to the public. However, the costs involved in undertaking high pollution traffic management were considered to be substantial because of the temporal, geographical and institutional extent of the activities that are likely to be involved. Some improvements in air quality were likely to be achieved with the most restrictive measures but the effort and costs involved were considered likely to outweigh the benefits. The report concluded that it would be better to have on-going long-term traffic management measures.

2.5 Working with Local Authorities to Deliver the Air Quality Strategy Objectives

We have a direct involvement with the review and assessment process in a variety of ways. These include providing the DMRB air quality screening method to estimate concentrations near roads, providing traffic data, monitoring pollutant concentrations, reviewing the local authority's reports and participating in action plan meetings which will lead to implementing measures to improve air quality.

2.5.1 DMRB Screening Method

We have recently updated the DMRB screening method to take account of revised vehicle emission rates, revised fleet composition data, changes to the Air Quality Strategy objectives and to improve the accuracy of the method. The performance of the method has been assessed by comparing estimated concentrations with measured values at DEFRA's AURN and our monitoring sites. The comparison can be seen at http://www.trl.co.uk/ (select calibration report). This revised screening method is the cornerstone of road assessments in the second phase of review and assessment.

2.5.2 Monitoring Concentrations

We currently monitor air pollution concentrations at four kerbside sites on our network - M60 Manchester, M25 Staines, M4 Theale and A40 Cheltenham. Details of the sites and the measured concentrations are hosted at http://www.trl.co.uk/. We also measure pollutant concentrations in the vicinity of a number of our larger schemes. This data is also available to the local authorities upon request, to assist with the review and assessment process. The local authority should liaise with the HA Project Sponsor for the scheme as to whether any monitoring is being carried out in the area. Modelled concentrations are also likely to be available for the scheme for a base year and an opening year both with and without the scheme.

2.5.3 Traffic Data

Traffic flows are routinely measured across the strategic road network using automatic traffic counters. There are two types of counter, a single loop that measures traffic flow only and a double loop that measures traffic flow and the number of heavy duty vehicles (> 5.2 m). These counters are 95% accurate. The data is regularly reviewed to identify any gaps or unusual results. Unusual results could be caused by a faulty counter or an incident on the local network. Erroneous data is removed and any gaps filled in. This data then forms the modified dataset. The data of most interest for review and assessment will be the annual average daily traffic (AADT) flows and annual average hourly flows throughout the day.

Traffic flows in future years can be estimated by applying growth factors to the measured flow data. Table 3 in the National Road Traffic Forecasts (Great Britain) 1997 provides forecasts of national growth for motorways, trunk roads and other roads in urban and rural areas . The forecasts are given as distance travelled relative to that in 1996, for 2001 and then every ten years. The annual average percentage increase (expressed as a factor) for each type of road is shown in Table 1 below. These factors should be used to estimate the growth between the year with measured traffic data and the year of interest.

Table 1 - Annual Factors to Estimate Traffic Flows
  Rural Urban
  Motorways Trunk & Principal1 Dual Other2 Motorways Trunk & Principal3 Dual Other4
1996-2001 1.0301 1.0192 1.0136 1.0192 1.0117 1.0192
2001-2011 1.0274 1.0161 1.0132 1.0161 1.0091 1.0184
2011-2021 1.0215 1.0125 1.0109 1.0096 1.0075 1.0149

Source: National Road Traffic Forecasts (Great Britain) 1997

Note: Urban areas are those of continuous built development, while all others are rural. The resulting traffic figures differ from the published traffic statistics presented on the build-up and non-build-up basis, which are solely determined by speed limits. Thus roads in urban areas with 50mph and higher speed limits are urban for the purpose of these forecasts, but non-built-up for traffic statistics.

For example, suppose measured traffic flows on a rural motorway were 100,000 AADT in 2000 and flows were needed for 2005 and 2010. The calculation would be:

2005 flow = 100,000 x (1.0301) 1 x (1.0274) 4 = 114,772

2010 flow = 100,000 x (1.0301) 1 x (1.0274) 9 = 131,382

Alternatively, if it is likely that using national traffic growth factors would not be representative of local conditions, then growth factors from TEMpro could be used. These can be obtained from http://www.tempro.org.uk/

Traffic speed is not routinely measured at the moment but a limited amount of data is available. If no local data is available, speed can be estimated from the speed-flow graphs given in DMRB Volume 13, Section 1, Part 5, Chapter 9. This can be viewed at http://www.standardsforhighways.co.uk/dmrb/index.htm

Traffic flows and speeds are held by consultants on our behalf. In due course, it will become available on the internet. In the meantime, it can be obtained from:

Southern Region (HA areas 1-5)
Richard Smith
Babtie
School Green
Shinfield
Reading
Berkshire
RG2 9HL
Tel: 0118 988 1608
Fax: 0118 988 1696
Email: hatraffic@babtie.com

Midlands Region (HA areas 6-9 and 11)
John Morris
Atkins Transport Planning
The Axis
10 Holliday Street
Birmingham
B1 1TF
Tel: 0121 483 5414
Fax: 0121 483 6161
E-mail: john.morris@atkinsglobal.com

Northern Region (HA areas 10, 12-14)
Martin Morson
WSP Transportation
6 South Park Way
Wakefield 41 Business Park
Wakefield
West Yorkshire
Tel: 01924 206628
Fax: 01924 368468
Email: martin.morson@wspgroup.com

2.5.4 Liaison with Local Authorities

By March 2003, 115 local authorities in England had declared Air Quality Management Areas. Just over half of these include HA roads. The AQMAs that include strategic roads are shown in Annex 2. Many of these are located near major conurbations such as the M25 near London, M60/M62/M66/M61 near Manchester, M4/M5 near Bristol, M5/M42 near Birmingham and various sections of the M1 in urban areas. Some of the AQMAs are near rural motorways where there are just a few dwellings close to the road whilst others cover entire boroughs. The size and number of AQMAs is subject to change as local authorities collect more monitoring data, revise traffic data and revisit the modelling as part of DEFRA's rolling programme for review and assessment. Some of the AQMAs declared for HA roads have been revoked as the monitoring data collected showed that measured concentrations were lower than those modelled, and it is likely that other revocations will follow.

Local authorities are required to consult with us if their review and assessment includes a strategic road. They should contact the route manager in the first instance. In the unlikely event that this proves to be unproductive, then Michele Hackman in the Environmental Policy team should be advised of the situation (Michele.Hackman@highways.gsi.gov.uk) Upon receiving a report, we will review it and pass our comments to the local authority. We will be particularly looking at the model result verification, the results from monitoring and the distance between the properties and the road. The number of properties affected and the highest predicted concentrations will also be of interest.

Once the AQMA has been declared, the local authority should invite the route manager to discuss how we can assist with improving air quality. A list of traffic management measures that could be considered is given in Annex 3. In delivering individual local measures to contribute to improved air quality, we must take into account the Government's five core policy objectives (environment, safety, economy, accessibility and integration) and assess how the proposed measure performs against these objectives. Further information on this is available in the Guidance on Methodology for Multi-Modal Studies. There must be a robust case for the mitigation measure for it to be considered further.

The action plan prepared by the local authority could include a suite of proposals to target the various causes of the emissions, for example, roadside emissions testing to reduce emissions from high emitting vehicles, workplace and school travel plans to reduce traffic flows, new developments to be served by public transport and accessible by non-motorised users to reduce additional demand, promotion and improvement of public transport to reduce traffic flows and junction improvements to reduce congestion.

Speed limit reductions are sometimes suggested as being a "quick-fix". Whilst in theory a significant speed reduction would deliver decreased emissions, in practice there are confounding factors and potential issues which need to be considered: roads are becoming increasingly congested so the benefits would be less than expected (please see section 3.1) with benefits decreasing in future years, a reduction in speed could increase capacity, this could lead to increased traffic flows, and most importantly, the speed limit would need to be enforced to ensure compliance which has high costs. As part of understanding these issues more thoroughly, we are assessing the possibility of a speed reduction on the M1 as part of our involvement in Sheffield's action plan.

The route manager should be able to comment on whether the proposals suggested by the local authority for strategic roads are feasible for the area concerned, whether any of our other projects may have an effect and whether further work should be carried out to assess the proposed mitigation measures in more detail. The local authorities should seek confirmation from the route manager that we are in agreement, subject to any further studies needed, with the measures proposed for the HA to implement.

2.5.5 The HA's Performance Targets

One of the Agency's key objectives is to respect the environment. A key performance target is set each year for air quality. In previous years this has been to respond to 95% of review and assessment consultations. In the current year it is to improve air quality in four AQMAS. We are currently considering a revised performance measurement for local air quality to better reflect the impact of the HA's activities.

In addition to the Agency's own performance targets for air quality, there is a Public Service Agreement (PSA) target that is jointly owned by the DfT and DEFRA. The target is "to improve air quality by meeting the Air Quality strategy targets for carbon monoxide, lead, nitrogen dioxide, particles, sulphur dioxide, benzene and 1,3-butadiene".

2. The Highways Agency's Role

3. What Effect Would it Have on Air Quality?

In order to work out the effect a scheme or action would have on air quality, information is needed on the following both with and without the scheme or action in place:

The DMRB screening method can be used to give an indication of the change expected for some actions such as changes to traffic flows, fleet composition in terms of vehicle type and daily average speed. The method is described in DMRB 11.3.1 and a spreadsheet is available to do the calculations. The data required for the spreadsheet are annual average traffic data and fleet composition, distance from property to each road centre within 200 m and annual average background concentration. However, the screening method is not suitable to assess the effect of some measures such as reducing congestion in peak hours, altering the speed by road lane, changing the proportion of vehicles meeting each Euro emission class or road lane usage.

More detailed calculations can be made by using a dispersion model. Detailed modelling can take account of, explicitly, variations in flows and speeds throughout the day, queuing traffic, local meteorological conditions, cuttings and embankments, road geometry, changes to age profile of vehicles, fleet composition and traffic description by lane. Further information is given in DEFRA's Review and Assessment: Technical Guidance LAQM.TG(03), which can be downloaded from www.defra.gov.uk/environment/airquality/laqm/guidance/index.htm.

3.1 Speed Changes

The graphs in Figures 1 to 5 below show the average vehicle emission rates of NOx, PM10, CO, non-methane hydrocarbons (NMHC) and CO2 in 2005 for a traffic flow with 5%, 10% and 15% heavy duty vehicles (HDV). The emission rates are tabulated in Table 2 for a vehicle fleet with 10% HDV.

Figure 1 - NOx Emissions by

Figure 1 - NOx Emissions by

Figure 2 - PM10 Emissions by Speed

Figure 2 - PM10 Emissions by Speed

Figure 3 - CO Emissions by Speed

Figure 3 - CO Emissions by Speed

Figure 4 - NMHC Emissions by Speed

Figure 4 - NMHC Emissions by Speed

Figure 5 - Carbon Dioxide Emissions by Speed

Figure 5 - Carbon Dioxide Emissions by Speed

Table 2 - Emission Rates (g/km) by Speed in 2005 for an average vehicle in the fleet (assuming 10% HDVs)
Speed (km/hr) NOx PM10 CO NMHC CO2
5 3.06 0.144 7.37 1.00 580.3
10 2.24 0.097 4.12 0.62 384.8
15 1.84 0.076 2.93 0.46 302.8
20 1.62 0.065 2.33 0.37 262.0
25 1.47 0.057 1.96 0.32 237.6
30 1.37 0.051 1.70 0.28 221.1
35 1.29 0.047 1.51 0.25 209.3
40 1.24 0.043 1.37 0.23 200.4
45 1.20 0.040 1.25 0.21 193.6
50 1.17 0.038 1.16 0.20 188.5
55 1.15 0.036 1.09 0.18 184.9
60 1.14 0.035 1.03 0.17 182.6
65 1.14 0.034 0.98 0.16 181.6
70 1.15 0.034 0.96 0.16 181.9
75 1.16 0.034 0.94 0.15 183.6
80 1.18 0.034 0.94 0.15 186.5
85 1.21 0.036 0.95 0.15 190.9
90 1.25 0.038 0.97 0.14 196.8
95 1.29 0.040 1.01 0.14 204.2
100 1.34 0.043 1.06 0.14 213.2
105 1.38 0.047 1.12 0.15 220.3
110 1.42 0.050 1.21 0.15 228.6
115 1.46 0.055 1.30 0.15 238.0
120 1.51 0.060 1.41 0.16 248.8
125 1.57 0.066 1.54 0.16 260.9

Source: DMRB Spreadsheet

The highest emission rates occur at the lowest speed of 5 km/hr for all of the pollutants. The lowest emission rates occur at 60-65 km/hr for NOx, 65-80 km/hr for PM10, 75-80 km/hr for CO, 90-100 km/hr for hydrocarbons and 65-70 km/hr for CO2. The increase with speed is greater for some pollutants, such as PM10, than for others, such as NOx where the speed curve is relatively flat.

The speed ranges over which emissions are within 10% of the minimum are shown in Table 3 together with the minimum emission speed range.

Table 3 - Speed Ranges with the Lowest Emission Rates (km/hr)
  NOx PM10 CO NMHC CO2
Minimum 60-65 65-80 75-80 90-100 65-70
Within 10% of minimum emissions 40-90 55-85 60-95 75-115 45-90

At low and high speeds, speed changes can have a more significant effect on emissions. Increasing speed from an hourly average of 5 km/hr to 10 km/hr could decrease emissions by 27% for NOx and 33% for PM10. Reducing the speed from 110 km/hr to 100 km/hr would decrease emissions by 6% for NOx and 14% for PM10. Reducing congestion is therefore important to improving air quality.

Some roads have considerable variation in speed from hour to hour with lower speeds during peak hours. The number of hours with congested traffic is likely to increase in the future as traffic flows increase. Table 4 contains traffic flow and speed data for a western section of the M25 together with the estimated hourly emissions in 2005 assuming that 10% of vehicles are HDVs. The daily emissions of NOx and PM10 are estimated to be 207.3 kg/km/day and 6.8 kg/km/day respectively.

If the speed had been assumed to be 112 km/hr throughout the day, the daily emissions of NOx and PM10 would have been estimated to be 225.9 kg/day of NOx and 8.0 kg/day of PM10, an overestimate of 9% and 18% respectively. However, if the daily average speed was used in modelling and the model results adjusted so that they were in agreement with the measurements, the overestimate would be removed. If future years were then modelled in the same way, the effect of any change to the speed variation throughout the day would not be reflected in the model results. As congestion is likely to increase in the future, this effect is likely to become more important.

It could be the case that one of the measures being considered in an action plan is to reduce the maximum speed limit to 100 km/hr. For the example discussed above, this would reduce emissions of NOx and PM10 by 1% and 2% respectively. However, if the speed had been assumed, incorrectly, to be a daily average of 112 km/hr originally, the emission reductions with a lower daily average speed of 100 km/hr would be estimated to be 6% for NOx and 14% for PM10, a larger reduction than would actually occur. Considerable care therefore needs to be taken when estimating the change in emissions that would result from a change in speed.

The estimated daily NOx and PM10 emissions for the scenarios discussed above are shown in Table 5.

Table 4 - Example Diurnal Profile of Emissions for the M25
Hour Traffic Flow (veh/hr) Speed
(km/hr)		 NOx emissions
(g/km/hr)		 PM10 emissions
(g/km/hr)
0 900 112 1,278 45
1 700 112 994 35
2 600 112 852 30
3 400 112 568 20
4 1,100 112 1,562 55
5 4,000 112 5,680 200
6 7,750 96 9,998 310
7 127,00 84 15,367 457
8 9,000 20 14,580 585
9 11,500 86 13,915 414
10 9,700 95 12,513 388
11 10,800 94 13,932 432
12 9,200 98 12,328 396
13 10,800 93 13,932 432
14 10,100 95 13,029 404
15 12,400 86 15,004 446
16 11,000 67 12,540 374
17 9,100 30 12,467 464
18 9,900 41 12,276 426
19 6,850 104 9,453 322
20 4,300 112 6,106 215
21 2,500 112 3,550 125
22 3,800 112 5,396 190
23 1,600 112 2,272 80
24-hour 159,100 - 207,320 6,765

Source: DMRB Spreadsheet

Table 5 - Comparison of Emission Estimates (g/km/day) for Various Speed Scenarios
Scenario NOx PM10
Actual speed 207,320 6,765
Constant speed of 112 km/hr 225,922 7,955
Maximum speed of 100 km/hr 205,582 6,642
Constant speed of 100 km/hr 213,194 6,841

3.2 Vehicle Type

Emissions from a range of fleet average vehicles in 2005, travelling at 100 km/hr on a motorway are compared in Table 6. The table also shows how many times greater the emissions are for each vehicle type compared to a car, for example, an articulated HGV has 21 and 24 times more emissions of NOx and PM10 respectively than a car. Proposals that encourage a modal shift from HGV to rail could be effective in some situations.

Table 6 - Comparison of Emissions from Each Vehicle Type in 2005
  Emissions (g/km) at 100 km/hr
  NOx PM10 CO NMHC CO2
Car 0.49 0.011 1.02 0.09 147
Light goods vehicle 0.91  (2) 0.125 (12) 0.95 (1) 0.09 (1) 243 (2)
Bus 5.62 (11) 0.084   (8) 1.12 (1) 0.26 (3) 663 (5)
Rigid HDV 5.09 (10) 0.113 (10) 0.76 (1) 0.35 (4) 687 (5)
Articulated HDV 10.52 (21) 0.265 (24) 1.86 (2) 0.84 (10) 1248 (8)

Source: DMRB Spreadsheet
Note: The number in brackets denotes the emission equivalent in terms of the number of cars.

Emissions will decrease in the future as vehicles meeting more stringent emission legislation penetrate the vehicle fleet. The change in average emissions for a vehicle fleet with 10% HDVs, travelling on a motorway at 100 km/hr in 2005 is shown in Figure 6 for NOx and Figure 7 for PM10. The results are tabulated in Table 7.

Emissions are expected to decrease by about 8% per year due to the penetration of the vehicle fleet by new vehicles but this will be offset to a small extent, by the increase in traffic. Any measures which encourage the uptake of newer, cleaner vehicles will improve air quality.

Figure 6 - Change in Average Vehicle NOx Emissions with Time

Figure 6 - Change in Average Vehicle NOx Emissions with Time

Figure 7 - Change in Average Vehicle PM10 Emissions with Time

Figure 7 - Change in Average Vehicle PM10 Emissions with Time

Table 7 - Change in Fleet Average Vehicle Emission Rates with Time
Year NOx PM10
1996 3.063 0.0840
1997 2.817 0.0740
1998 2.621 0.0697
1999 2.373 0.0667
2000 2.117 0.0577
2001 1.932 0.0548
2002 1.742 0.0512
2003 1.577 0.0481
2004 1.442 0.0454
2005 1.341 0.0433
2006 1.247 0.0401
2007 1.153 0.0360
2008 1.064 0.0322
2009 0.966 0.0289
2010 0.883 0.0261
2011 0.815 0.0240
2012 0.758 0.0223
2013 0.709 0.0209
2014 0.668 0.0197
2015 0.638 0.0190

3.3 Modal shift from cars to buses

The effectiveness in reducing emissions by persuading car drivers to travel by bus either through park and ride schemes or improved public transport will depend upon a number of factors. These include the emissions of each vehicle (determined by EU emission legislation), the number of cars that each bus effectively removes from the road, and any additional distance that the car travels to reach the bus. Table 8 shows the emissions at 50 km/hr for a 2005 fleet average car, 2005 fleet average bus and each Euro class bus.

The bus emissions are higher than those than from a car for all pollutants except carbon monoxide. Eighteen fleet average cars would need to be removed from the road network for each additional fleet average bus in 2005 if there were to be a reduction in emissions of all pollutants. However, the modal shift could have a greater reduction in emissions if newer, cleaner buses were used.

Table 8 - Comparison of Emissions from Cars and Buses
  Emissions (g/km) at 50 km/hr
  NOx PM10 CO NMHC
Fleet average car 0.32 0.008 1.17 0.13
Fleet average bus 5.52 (17) 0.104 (12) 1.05 (1) 0.32 (2)
Euro I Bus 6.43 (20) 0.230 (27) 1.25 (1) 0.55 (4)
Euro II Bus 5.81 (18) 0.139 (16) 1.02 (1) 0.44 (3)
Euro III Bus 4.01 (13) 0.100 (12) 0.72 (1) 0.31 (2)
Euro IV Bus 2.85 (9) 0.021 (3) 0.52 (1) 0.22 (2)

Source: Emission factors for fleet average car and bus - DMRB spreadsheet, for Euro bus - National Atmospheric Emissions Inventory, Emissions Factor Database http://www.naei.org.uk/emissions/index.php

Note: The number in brackets denotes the minimum number of fleet average cars in 2005 that would have to be removed from the road network for each additional bus, for there to be a decrease in emissions.

3. What Effect Would it Have on Air Quality?

References - Corporate Documents

Main Reports

Strategic Plans

References - Corporate Documents

Annex 1 - Road Schemes in the TPI

Current schemes

Future Schemes

Annex 1 - Road Schemes in the TPI

Annex 2 - Air Quality Management Areas that include Strategic Roads

The HA keeps a record (106KB PDF) of all the Air Quality Management Areas on the strategic road network. This indicates the location of the AQMA, the Action Plan measures the local authority has put forward, and HA schemes that may deliver air quality benefits.

Further information is available on these Air Quality Management Areas (please note this is an external website).

Air Quality Management Areas Map

Annex 2 - Air Quality Management Areas that include Strategic Roads

Annex 3 - Traffic Management Measures

The following table contains a number of traffic management actions that may be considered, in some situations, as a means of reducing traffic emissions. The actions have been classified into five main groups: speed controls, access control, provision of information, segregation of traffic and junction design. However, there can be considerable overlap between these groups (e.g. priority given to certain vehicles at a junction could be classed under segregation of traffic and junction design, and might include elements of information provision through improved signing).

With each action, a short description is given of its possible effects, but these will vary significantly depending on the precise local circumstances, and they should be evaluated on a case-by-case basis. Combinations of actions may well be more effective than any one in isolation. These actions do not include measures to reduce traffic demand which should form part of an action plan.

Primary control area Action and possible impact on traffic
Speed Enforcement of existing limits:  Reduces the proportion of vehicles exceeding the speed limit.  Only a few vehicles likely to be affected directly
Permanent speed limit reduction: Reduces the average traffic speed if enforced but could increase road capacity.
Vehicle class specific speed limits: May produce small improvements if coupled with class segregation by lane.
Improved signing: May improve compliance with limit
Controlled motorways (variable speed limit depending on traffic flow with lower speed limits during busy periods ):  Can reduce congestion by delaying the onset of flow breakdown and encourages a smoother driving style but may increase road capacity. 
Traffic calming (rumble strips, colour bands, road surface changes etc.): May encourage compliance with limit and could affect route choice but may not produce a decrease in emissions.
Access control Ramp metering (restricting access from the slip road onto the motorway): Can improve flow on the primary road ie reduce congestion, but there is the potential for queuing at the metering point.
Zone restriction e.g. clear zone, low-emission zone, home zone, no stopping / parking zones etc: Can improve conditions in the restricted zone but traffic may be diverted.
Width restrictions: Reduction in road capacity or restriction on large vehicles, drivers may slow to negotiate restriction or may divert to an alternative route.
Park and ride encouragement: Affects modal split, mainly in town centres but needs to reduce traffic flows to be effective.
Information provision VMS messages:  Information on available parking spaces or road closures can affect traffic flow, usually for the better. On motorways they can benefit traffic flow if providing diversion information. May be possible to display other messages relating to air quality.   
Driver training improvements: Can encourage low-emission vehicle operation.
Route/diversion information: Good impact, can relieve potential queues
Alternative route provision: Good impact, can relieve potential queues
Radio/Internet/TV traffic announcements e.g. RDS-EON etc : Need to be accurate and up-to-date.
Advanced warning of road repairs and closures, bad weather, major events etc : Allows motorists to plan alternatives.
Improved public transport information - e.g. timetable information and route provision via VMS or at displays at service stations : Can encourage the use of public transport for whole or parts of journeys.
Use of motorway service areas as an interchange for park and ride:  Use of existing facilities. Could help alleviate strain on certain parts of the network.
Segregation of traffic Dedicated lanes - bus, HOV, cycle, taxi, single occupant etc : Improved flow for prioritised vehicles but perhaps negative impact on other traffic.
Tidal lanes (varying number of lanes depending on time of day) : Make efficient use of road space.
Climbing lanes:  Help keep most traffic moving at acceptable speeds.
Signal priority : See dedicated lanes.
HGV or LDV dedicated routes:  Can benefit dedicated vehicle type and other traffic.
Lane closures : Could discourage local traffic from using certain stretches of trunk roads.
Junction design Improved signing:  Prevents hesitation at junction, helping to maximise throughput, reduces congestion.
Access closure - closure of side road:  Improves flow on the principal road.
Choice of appropriate junction, e.g. cross road with or without lights, roundabout with or without lights, at-grade or grade separated, dedicated slip lanes, etc:  Established procedures exist for junction design. The most appropriate type is selected on the basis of the ratio of the major to minor arm flow. Clear lane markings, optimised traffic lights may be added.

Many of these actions could be taken in a responsive way and could be optimised differently under different flow conditions, at different times of day, at times of high pollution, etc.

Annex 3 - Traffic Management Measures