Low Emission Zones

This measure was provided by THE URBAN PLANNING INSTITUTE OF THE REPUBLIC OF SLOVENIA (UIRS) in 2014 under the CH4LLENGE project, financed by the European Commission.

Low Emission Zones (LEZs) are areas where access by vehicles is limited to those with low emissions. They tend to be focused on city and town centres, where land-use is dense, traffic is heavy and population exposure is high. A number of cities and towns in different countries around Europe operate or are preparing LEZs to help meet the EU health-based air quality limit values. In different countries LEZs are also known as Environment Zones, Umweltzonen, Milieuzones, Lavutslippssone, Miljozone or Miljözon.

LEZs are designed and implemented to reduce the emissions of harmful pollutants from road traffic and to improve air quality. The emissions that are targeted for reduction in LEZs are mainly fine particles, nitrogen dioxide and indirectly ozone.

Indirectly through air quality they have impacts on the quality of life in the cities. Air pollution causes lost working days, and high healthcare costs, with vulnerable groups such as children, the elderly and others with respiratory problems or asthma. It damages ecosystems through excess nitrogen pollution (eutrophication) and acid rain.

They are also one of the more promising options for introducing greater numbers of cleaner vehicles, and reducing the numbers of older, more polluting vehicles on the road network. Although traffic volumes in LEZs do not necessarily change, vehicles travelling in an area have lower emissions, and this leads directly to air quality improvements.

LEZs differ in targeted vehicles and in their approaches to enforcement. Vehicle emissions are most commonly classified by the emissions standard or so-called "Euro Standards" for the vehicles that they affect. LEZs normally affect heavy duty goods vehicles. Some also affect diesel vans, buses and coaches, cars and motorcycles. This means that vehicles may be banned or in some cases charged if they enter the LEZ when their emissions are over a set level.

Most LEZs are manually enforced, but cameras and transponders are also used. Most schemes operate permanently, with some exemptions where LEZs operate at peak times, weekday daytime or weekday daytime and evening.

Costs of LEZ implementation depend mainly on the complexity of the scheme, the technology chosen and the system of enforcement. Some LEZ schemes are therefore cheaper to implement than others.

Introduction

The UK Department for Environment, Food and Rural Affairs (DEFRA) states that: “A Low Emission Zone is a geographically defined area where the most polluting of vehicles are restricted, deterred or discouraged from access and use. The aim is to reduce the number of more polluting vehicles being used in a particular area by setting particular emission standards or criteria, with the aim of improving the air quality.”(DEFRA, 2009)

Low Emission Zones (LEZs) tend to be focused on city and town centres, where land-use is dense, traffic is heavy and population exposure is high. There is the highest value in such areas from restricting, discouraging or deterring the use of more polluting vehicles. Previous studies have demonstrated that the most common vehicles to target in a scheme with enforceable restrictions are diesel powered Heavy Duty Vehicles (HDVs) due to their cost-effectiveness relative to schemes that would restrict other vehicle types (DEFRA, 2009).

Terminology

LEZ are also known as Environment Zones, Umweltzonen, Milieuzones, Lavutslippssone, Miljozone, Miljözon (LEEZEN, 2013).

A Zero-Emission Zone (ZEZ) is a LEZ where only Zero-Emission Vehicles (ZEVs) are allowed. In such areas, all internal combustion engine vehicles are banned; this includes hybrid vehicles. Only all-electric vehicles are allowed in a ZEZ, along with walking and cycling and fully electric public transport vehicles, e.g. trams, electric buses (Wikipedia).

Description

LEZs are one of the more promising options for introducing greater numbers of cleaner vehicles, and reducing the numbers of older, more polluting vehicles on the road network. A LEZ prohibits older vehicles from operating in an area, and so accelerates the turnover of the vehicle fleet (or requires operators of older vehicles to fit abatement equipment to their vehicles).  Although traffic volumes do not necessarily change, vehicles travelling in an area have lower emissions, and this leads directly to air quality improvements (AEA, 2003).

A number of cities and towns in different countries around Europe operate or are preparing LEZs to help meet the EU health-based air quality limit values, where the most polluting vehicles are regulated (Wikipedia). Different vehicles are regulated, depending on the local conditions. All LEZs affect HDVs (usually over 3.5 tonnes Gross Vehicle Weight). Studies have shown that diesel-fuelled goods and service vehicles (vans, lorries, buses and coaches) are responsible for disproportionate amounts of the total road traffic emissions of fine particulate matter (PM10). Some LEZs affect diesel vans, buses and coaches. German and Italian LEZs also affect cars and motorcycles. Vehicle emissions are classified by the emissions standard or so-called "Euro Standards" for the vehicles that they affect. In many cases another factor is whether or not the vehicle has a particulate filter or catalytic converter. The emissions that are targeted for reduction by LEZs are mainly fine particles, nitrogen dioxide and indirectly ozone (LEEZEN, 2013).

European emission standards define the acceptable limits for exhaust emissions of new vehicles sold in EU member states. Currently, emissions of nitrogen oxides (NOx), total hydrocarbon (THC), non-methane hydrocarbons (NMHC), carbon monoxide (CO) and particulate matter (PM) are regulated for most vehicle types. The legislation was initially introduced in 1993 (Euro 1) and was tightened in 1996-1997 (Euro 2) and in 2001 (Euro 3).  Legislation has subsequently imposed further controls in 2006 (Euro 4), 2008/9 (Euro 5) and 2014 (Euro 6). The faster adoption of cleaner road vehicles therefore offers an opportunity for reducing emissions. 

There are many LEZs in many European countries with differences in targeted vehicles and with different approaches to enforcement. Most LEZs are manually enforced, but cameras and transponders are also used. Given constraints on budgets for operating costs, a scheme which has low operating costs will tend to be more attractive from a whole-life cost viewpoint. However, this needs to be carefully balanced against the resulting level of compliance by users with the scheme emission standards, or the purpose and value of the scheme will be undermined. A general overview of LEZ schemes country-by-country is shown below:

• Manual enforcement is used in the Swedish, Austrian motorway and German LEZs.
• The Dutch LEZs started with manual enforcement but have now moved to camera enforcement.
• Most Italian LEZs are manually enforced however a few have camera or even electronic enforcement, often when combined with another scheme or pedestrian zone.
• The Danish LEZs set out the three manual enforcement methods: Firstly municipal inspectors when lorries are visiting a company; Secondly town traffic wardens checking vehicles parked on the street; Finally, police at routine roadside checks. Both inspectors and traffic wardens can call on the police when needed.
• The London LEZ and Milan Ecopass are camera enforced.
• The Norwich and Oxford LEZs (UK) are enforced through agreements with the local bus operators.
• The planned Norwegian LEZs intend to use the same electronic device system as used for motorway tolls (Autopass), with camera and manual enforcement also possible, as well as cameras to enforce those who do not pay.

In Germany, Denmark, and Sweden the driver needs to buy a sticker. Foreign vehicles are required to register with London’s LEZ (as the national database does not include their details). Entry to the Prague's LEZ is by permit, to Budapest’s parking by emissions-related payment. The Bolzano (Italy) LEZs require stickers and the driver needs to pay to enter the Central Milan 'Area C'. In many cases registration is possible by Internet or post.

Other LEZs are enforced with cameras reading the vehicle number plates (Netherlands, London), or by police controlling the vehicle papers (Italy, Austrian A12 motorway, Mont Blanc Tunnel), or local agreements with public bus operators (Norwich, Oxford (UK)). Lisbon currently uses police controlling vehicles papers, but is planning more automated enforcement.

Most LEZs operate permanently. The exemptions are Italy, where LEZs sometimes operate at peak or other selected times; Lisbon, Prague and Budapest LEZ are weekday daytime, Athens is weekday daytime and evening (LEEZEN, 2013).

Why introduce LEZs?

The concept of a LEZ is primarily concerned with improving the air quality in urban areas by reducing the adverse impact of the most polluting motor vehicles. LEZs normally affect heavy duty goods vehicles. Some also affect diesel vans, buses and coaches, cars and motorcycles. This means that vehicles may be banned or in some cases charged if they enter the LEZ when their emissions are over a set level.

In European countries LEZs are usually operating to help cities meet the EU health-based air quality limit values. According to the European Commission the human toll for poor air quality is worse than for road traffic accidents, making it the number one environmental cause of premature death in the EU. It also impacts the quality of life due to asthma or respiratory problems. Air pollution causes lost working days, and high healthcare costs, with vulnerable groups such as children, asthmatics and the elderly the worst affected. It damages ecosystems through excess nitrogen pollution (eutrophication) and acid rain. The direct costs to society from air pollution, including damage to crops and buildings, amount to about €23 billion per year, and the external costs from health impacts alone are estimated at € 330-940 billion (3-9% of EU GDP) (EC, 2014). 

Demand impacts

The impacts of LEZs are mainly on reduced air pollution from polluting motor vehicles. The responsiveness of the demand for vehicle travel in relation to LEZs depends upon the availability of alternatives and other supporting measures.

Short and long run demand responses

Supply impacts

LEZs would not involve any significant change in overall road supply. Even if demand is reduced through modal change and improved alternatives (e.g. public transport, consolidate freight delivery) as a result of LEZ implementation, the amount of road space available to each individual vehicle would increase only a little, particularly at peak times.

Financing requirements

Costs of LEZ implementation depend mainly on the complexity of the scheme, the technology chosen and the system of enforcement. Some LEZ schemes are therefore cheaper to implement than others.

DEFRA guidance (2009) provided an example of the cost analysis for a LEZ, which is shown below. It compares alternative options where the Base scheme refers to an access control scheme giving priority to public transport in a small city centre area, enforced using Automatic Number Plate Recognition (ANPR) cameras. Schemes A to C are potential developments of this Base scheme into a LEZ, with progressively greater numbers of vehicles required to meet specified emissions criteria. Schemes A to C require additional ANPR camera sites, plus accompanying back-office systems and operating staff. First the cost estimates are presented, showing the cost elements for capital and operating costs for a base scenario, and then three alternative schemes comparing different vehicle types.

The following cost estimates (£ Million) were calculated in a feasibility study for the recommended London LEZ Scheme (AEA, 2003):

Expected impact on key policy objectives

According to DEFRA (2009), it is likely that LEZ schemes will have significant impacts on environmental objectives as improving the environment is their key objective. The nature of the impacts will be scheme specific and depend on the scheme location and the scheme’s impact on traffic levels by location, time of day and the composition of traffic. The environmental impacts of a scheme will also depend on the extent to which the LEZ is combined with other measures (DEFRA, 2009).

Expected impact on problems

Expected winners and losers

Barriers to implementation

The Environmental zone in Berlin

In the city centre of Berlin the limit values for PM10 and nitrogen dioxide NO2 have been exceeded in many major streets. The road traffic was one of the most important origins for these pollutants in Berlin’s city centre contributing around 40% of PM10 and about 80 % of NO2 emissions. The environmental zone in Berlin was implemented in the beginning of 2008. It includes the inner city of Berlin within the suburban rail ring which is about 88 km2 of a very densely built-up area with one million inhabitants.

Vehicles entering the area must be equipped with a wind screen sticker, describing in which of the four pollutant classes they belong. The classes follow the Euro standards for vehicles with diesel engines. For vehicles with petrol engines there are two classes, pollutant class 1 without a windscreen sticker for vehicles that do not meet the Euro 1 standard, and pollutant class 4 for all vehicles meeting the requirements of Euro 1.

In phase 1 (2008) only vehicles with stickers of classes 2, 3 and 4 were allowed to enter the zone. Since 1st January 2010 (phase 2) only vehicles in class 4 with green stickers are allowed. However, vehicles with a yellow sticker, that are registered abroad, are exempted from the traffic ban in the environmental zone until 31 December 2014. Vehicles registered abroad will be classified either on the basis of documentary evidence that they meet the European emission standards or according to their initial registration date. The following table is intended to give a general overview for passenger cars, but there may be variations in individual cases (source: www.berlin.de/umweltzone)

Evaluation results of the phase 2 extension of Berlin environmental zone showed the following results:

• the implementation of phase 2 caused no serious problems; the biggest problem was the capacity to retrofit vehicles with particulate traps
• accelerated modernisation of the vehicle fleet (in the city and metropolitan area)
• reduction in diesel soot (BC) emissions: by 58 %
• reduction in nitrogen oxide (NOx) emissions: by 20 %
• reduction in PM10 emissions: by 7-10 % (Eltis, 2008)

London Low Emission Zone 

The London Low Emission Zone scheme is designed to reduce the emissions of harmful pollutants from road traffic in London and, in conjunction with a wider range of related air quality improvement initiatives, to help London move towards achievement of UK and European air quality objectives. The scheme is administered by Transport for London (TfL) with the aim of reducing the emissions of diesel-powered commercial vehicles in London.

The LEZ was created in February 2008. The zone covers most of Greater London (with minor deviations to allow diversionary routes and facilities to turn around without entering the zone and the M25 motorway) – an area of around 1500 square km. The boundary of the zone, which operates 24 hours a day, 7 days a week, is marked by signs.

It initially required vehicles weighing more than 12 tonnes to meet ‘Euro III’ emissions standards. In July 2008, this was extended to freight vehicles with a weight of more than three and a half tonnes, as well as buses and coaches over five tonnes. By 2012, large vans and minibuses were also required to be compliant with these restrictions.

The scheme works by requiring operators of goods and service vehicles in London to meet minimum emissions standards, defined with reference to the ‘Euro’ emissions standards, from certain specified dates. Operators of affected vehicles in London are required to ensure that their vehicle meets the required emission standard. If this is not the case, then operators of non-exempt vehicles that do not comply with the requirements of the scheme are subject to a daily charge of £200 (£100 for vans and minibuses). The LEZ is different from the London Congestion Charge zone – the former covers all of Greater London, whilst the latter covers only a very small area of the central city.

Non-GB registered vehicles that meet the required LEZ standards need to register with TfL; most compliant GB registered vehicles do not. Owners of vehicles that do not meet the above requirements have a number of options:

• Fit a filter
• Replace the vehicle
• Reorganise their fleet to only use compliant vehicles in London
• Convert to natural gas
• Pay the charge (from £100 to £200 for each calendar day that the vehicle travels within the zone)

The zone is monitored using Automatic Number Plate Reading Cameras to record number plates. Vehicles entering or moving around the zone are checked against the national database of registered vehicles. For vehicles registered outside of Great Britain, an international debt recovery agency is used to obtain unpaid charges and fines.

Despite significant improvements in recent years, London's air pollution is still a concern. So, in January 2012, the LEZ emissions standards became more stringent. More vehicles are affected, and those that were already affected need to meet tighter emissions standards. In February 2013, the Mayor announced that the next phase of the LEZ will only apply to the buses they operate in 2015. Operators of diesel lorries and coaches do not need to take any action.

Allen (2006) reports that the estimated cost of the LEZ scheme to Transport for London (TfL) was between £125 million and £130 million, from development of the scheme until 2015/16. This range reflects different scenarios around how operators would respond to the proposed LEZ, and the scope and cost of services from DfT. The capital costs are approximately £45 million (approximately 57 million €), which include all development, consultation and implementation costs. The total operating costs of the scheme from early 2008 to 2015/16 are estimated at between £80 million and £85 million (approximately 100 – 110 million €).

There would also be costs to operators from complying with the LEZ. The costs to operators of the core LEZ scheme are estimated as being between £195 million and £270 million (approximately 245 – 340 million euros) for the period to 2015/16.
The proposed LEZ is not designed to be a revenue generating scheme and the revenues do not offset the costs of implementing and operating the scheme. Air quality improvements would be maximised by high levels of operator compliance which would mean minimal payments into the scheme. There would, however, be some revenues from the LEZ through charge and penalty charge payments. Revenues are expected of between £30 million and £50 million during the life of the scheme, from 2008 to 2015, and these would contribute towards the operating costs of the scheme (Allen, 2006).

Key Evidence

One of the aims of the London scheme was to create an incentive for businesses to replace existing vehicles with newer and less polluting models. According to Ellison et al. (2013) data from the UK’s Driver and Vehicle Licensing Agency showed that the number of rigid vehicles (medium or heavy duty lorries without a trailer) not meeting EU emission standards dropped substantially in 2008, suggesting that the LEZ resulted in an extra 20% of vehicles being replaced by lower-emission vehicles.

The results show that the LEZ is driving a reduction in ‘non-compliant’ vehicles, i.e. those that do not meet the stricter EU emission standards; the number of articulated vehicles non-compliant with EU emissions regulations has halved since 2007, and the proportion of non-compliant ridged vehicles used in the LEZ dropped by 6% to 22% in 2009.

From 2001, data on levels of particulate matter and nitrogen oxides, both produced by traffic, were recorded at four locations, three within the LEZ and one 25 km away. Particulate matter concentrations were found to be stable or decreasing at the three sites within the LEZ, after introduction of the scheme.

Nitrogen oxide concentrations fell both inside and outside the LEZ and were not significantly different between locations. Overall, the authors conclude that the LEZ has had a substantial impact on the composition of the vehicle fleet, increasing the proportion of low-emission vehicles. This in turn has led to a small but significant improvement in air quality (EC, 2013 citing Ellison et al., 2013).

Swedish Low Emission Zones

Low Emission Zones have been in place in Sweden since 1996, when Stockholm, Gothenburg and Malmo introduced ‘Environmental Zones’ in their city centres, with the purpose of improving air quality and reducing noise. The zones target all diesel lorries and buses over 3.5 tonnes.  On introduction, the scheme required all these vehicles to meet the Euro 1 standard.  Vehicles between 9 and 15 years old were also allowed to operate in the zone if they had been retrofitted with a certified emissions control device or new engine.  There was also a special permit for vehicles that only travelled rarely in the zone.  The zone is enforced using a permit system for older vehicles (windscreen stickers) with visual inspections.  Vehicles driving illegally in the zone are subject to a fee, enforced by police authorities.  The zone does not have any signage.  The compliance rate is around 90% (based on visual inspections).  The zone is simple and has low costs to administer. 

From January 2002, the environmental zones (Stockholm, Gothenburg, Malmo and Lund) introduced an 8 year age limit from date of first registration on all heavy-duty vehicles (>3.5 tonnes).  Older vehicles, with first year of registration after 1993 (i.e. minimum Euro 1) may enter the zone with the approved after treatment device.  A two-tier system was introduced.  Level B, which requires the retrofit technology to reduce emissions of particulates and hydrocarbons by 80%, and level C, which requires an additional 35% reduction in NOx.  For both levels, no increase in noise levels is allowed with the retrofit technology.  Level B corresponds with a particulate filter and catalytic converter and level C with current NOX reduction equipment.  Vehicles meeting level B requirements are allowed to operate for another 4 years in the zone (i.e. until 12 years old).  Vehicles meeting level B+C requirements are allowed to operate for an additional 2 years on top of this (i.e. until 14 years old).  Special conditions are set out for vehicles with a special body.  For these vehicles (even if pre-Euro), vehicles over 8 years old are allowed to enter the zone with relevant emissions after-treatment equipment.  In addition, vehicles meeting the level B emissions requirements are permitted to operate for longer (vehicles between 8 and 15 years are allowed to enter the zone if they meet level B emission requirements and an additional 2 years on top of this if they meet B+C requirements). Vehicles are also allowed to enter if they re-engine.  For example, if a new engine is put into a vehicle after January 2002, the vehicle may enter the zone for a maximum of 6 years from the year of manufacture of the engine (provided the engine meets the most severe European environmental class at that time).  It may also enter the zone for longer if the level B and B+C emission requirements are met through additional approved abatement equipment.

In Stockholm, the environmental zone covers around 30% of the total population of the city (i.e. an area with around 220,000 people).  An assessment of the air quality benefits of the scheme in 2000 (Johansson and Burman) found that emissions of NOX from heavy vehicles within the zone were reduced by 10% and emissions of particulates by 40%.  These benefits are relative to the emission reductions that would have occurred from heavy vehicles (only) without the zone.  The corresponding reductions in air pollution concentrations were estimated at 1.3% reduction for NOX (with a range of 0.5% - 2%) and 3% for particulates (with a range of 0.5% to 9%), compared to the predicted concentrations without the zone.  The values are much lower than with emissions because of the importance of other road vehicles and other sources to total air quality concentrations.  The analysis also concluded that the effect of the environmental zone was large when compared with other actions that it was possible for the local city administration to implement.

Statistics from Stockholm also show that vehicles registered in the municipality (City) of Stockholm are younger in general, compared to vehicles registered in Stockholm County. This is most distinct regarding trucks.
The comparison of the Swedish and London studies provides some interesting conclusions. The Swedish schemes have achieved very large emissions improvements, because they were introduced early, when the fleet had higher emissions (i.e. by targeting pre-Euro vehicles).  Essentially, because the London scheme was introduced later, the benefits are mitigated by the ongoing improvements in the vehicle fleet as a result of the Euro standards.

Interestingly, the London study also found that a London low emission zone would have a greater impact in improving air quality concentrations than it would in reducing emissions, at least in relation to the specific air quality targets set by the UK Government and the European Union.  This happens because many locations in London are likely to be close to the air quality target levels for future years.  Even small changes in emissions can significantly affect the area of exceedance, so that an area that previously exceeded the air quality target could drop below the threshold level with the introduction of a low emission zone in place.

Some analysis of the costs of the Swedish LEZs has been compiled. Swedish cities are rather small – the Stockholm scheme affects 7,000 heavy vehicles, whereas the London scheme (potentially) affects as many as 30,000 to 70,000 heavy vehicles.  While small businesses were identified as being affected by a potential Swedish zone, no special measures were introduced to assist these businesses.  The cost of compliance of the Stockholm scheme was estimated at around 37 M crowns (1€ = 9.5 crowns), with other schemes in Gothenburg and Malmo estimated at 14 M crowns and 11M crowns respectively for 1997.  The actual costs in Stockholm were found to be around half the estimated value, while the costs in the other two cities were about the same as those predicted. No attempt was made to estimate the social and economic costs of the schemes.  The Swedish scheme did consider a five-year, rather than an eight-year cut-off for eligible vehicles (the recommended proposals for the London LEZ effectively introduce a 5 year age limit).  However, this tightened age limit was ruled out in Sweden because most vehicles had an eight-year warranty and a feasibility study indicated that the 5-year age limit would result in very high costs to business.

A CBA was undertaken for the Swedish environmental zones and the analysis estimated that 80% of the costs of the zone had been offset by direct gains for the environment. Unfortunately the data is not available to re-assess the cost benefit ratio with the new unit pollution values used in other areas of the report.

Contribution to objectives

Contribution to problems

Appropriate contexts

Adverse side-effects

The main limitation with a LEZ is that it only accelerates the introduction of new vehicles, therefore it only brings forward emissions and air quality improvements that would have occurred (in time) anyway.  The London study (AEA, 2009) showed that most LEZ schemes would have a modest reduction in emissions and improvement in air quality.  The reason is that the air quality benefits of any LEZ have to be seen in the context of a significant decrease in emissions, year on year, as a result of the ongoing, normal replacement of older vehicles by newer vehicles in the fleet. Nonetheless, when compared to other options in London, the potential for an LEZ was seen as one of the most cost-effective methods of achieving (relatively) large-scale improvements (AEA, 2009). 

As mentioned before, the most common vehicles to target in a scheme with enforceable restrictions are diesel powered Heavy Duty Vehicles (HDVs) due to their cost-effectiveness relative to schemes that would restrict other vehicle types. It is important to note that in many city centres the majority of HDVs are buses. This can lead to conflict with other sustainable transport objectives related to modal shift to public transport.  LEV buses are more expensive than diesel buses so if cities put resources into cleaner buses they have less resource for better public transport service.  And if they ban buses from city centres, they ban them from their most important traffic generator.

Defra (2009) advises local authorities to implement a package of local air quality measures rather than just LEZ - reducing the number of more polluting vehicles might be achieved by a range of other methods. For example, incentivisation mechanisms, partnerships or regulations that focus on specific sectors of road transport might be used to encourage lower emission vehicles or take up of emission abatement technologies. It would also be possible to combine different schemes as part of an overall emissions reduction strategy (Defra, 2009).

The feasibility study for London LEZ (AEA, 2003) showed that it is also important to recognise that such scheme would have significant cost implications for vehicle operators. The study has clearly shown that the costs to operators are likely to exceed the costs of setting up and running a London LEZ.  The concern was stronger for smaller operators, who often have longer replacement cycles, and owners of vehicles with specialist bodies (e.g. cement lorries), which also have longer replacement cycles as these vehicles are more expensive and tend to do less mileage (AEA, 2003). 

AEA (2003) The London Low Emission Zone Feasibility Study. A Summary of the Phase 2 Report to the London LEZ Steering Group. AEA Technology Environment, Oxon. https://www.tfl.gov.uk/cdn/static/cms/documents/phase-2-feasibility-summary.pdf

Allen, J. (2006) London Low Emission Zone. Case study description for OSMOSE project. Transport Studies Group, University of Westminster, London. http://www.osmose-os.org/

Boogaard, H., Janssen, N.A.H., Paul H. Fischer, P.H. et al. (2012) Impact of low emission zones and local traffic policies on ambient air pollution concentrations. Science of the Total Environment. 435-436:132-140.

DEFRA (2009) Local Air Quality Management: Practice Guidance 2 - Practice Guidance to Local Authorities on Low Emissions Zones. Department for Environment, Food and Rural Affairs, London. http://archive.Defra.gov.uk/environment/quality/air/airquality/local/guidance/documents/practice-guidance2.pdf

C Ellison, R.B., Greaves, S.P. & Hensher, D.A. (2013). Five Years of London’s low emission Zone: Effects on vehicle fleet composition and air quality. Transportation Research Part D 23: 25-33.

EC (2013) Five years on: changes to vehicle fleets and air quality in London’s low emission zone. Science for Environment Policy. European Commission DG Environment News Alert Service, edited by SCU, The University of the West of England, Bristol. http://ec.europa.eu/environment/integration/research/newsalert/pdf/338na3.pdf

http://eltis.org/index.php?id=13&lang1=en&study_id=1817 (accessed 8th August, 2014)

Frey, K (2010) The Low Emission Zone (Umweltzone) in Berlin. Presentation at Sustainable + healthy urban transport workshop, Skopje, 7- 8 June 2010. Federal Environment Agency Germany. http://www.unece.org/...low.emission.zone.pdf

LEEZEN (2013) Low Emission Zone in Europe Network. Sadler Consultants Ltd, Bristol. http://urbanaccessregulations.eu/

UBA (2014) Umweltzonen in Deutschland. Umwelt Bundesamt. Dessau-Roßlau. http://gis.uba.de/website/umweltzonen/php/umweltzonen.php