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New services and equipment helps cities tackle air quality issues

First publishedin ITS International
July August 2017
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Opportunity charging extends the range of Volvo's 7900 all-electric bus.jpg
Opportunity charging extends the range of Volvo's 7900 all-electric bus
With poor urban air quality shortening lives and fines being imposed for breaching pollution limits, authorities are seeking ways to clean up their cities.


Poor air quality is topping the agenda for city authorities across the globe. In the UK, for example, a report from the Royal Colleges of Physicians and of Paediatrics and Child Health, concluded that poor outdoor air quality shortens the lives of around 40,000 people a year – principally by undermining the health of people with heart and/or lung problems. On a wider scale, the European Environment Agency says around 90% of Europe’s city dwellers are exposed to pollution levels deemed harmful to health. It cites fine particulate matter (PM2.5) in the air as the key problem which is estimated to reduce life expectancy in the EU by more than eight months.

Another report, this time by Westminster City Council in central London, identifies road traffic as the predominant source (almost 65% and 58% respectively) of two major pollutants, PM2.5  and NO2. Gas heating in buildings is also identified as producing 32% of the NOx in London’s air as well as 11.5% of the PM2.5.  

That air quality is deteriorating is directly linked to increased congestion, according to a report by Professor David Begg, former chairman of the government’s Commission for Integrated Transport, and Claire Haigh, chief executive of Greener Journeys. Transport for London’s (TfL) city-wide data shows average morning peak traffic speeds fell from 16km/h in 2006 to 12km/h in 2016. The authors conclude this slowing of traffic has caused a 10% increase in NOx emissions from diesel cars and vans while for buses and trucks the increases are 25% and 27% respectively.

There is more evidence of emissions being increased by stop-start traffic in work done by the University of Southampton Transportation Research Group for the UK Department for Transport. This has shown that the NOx reduction efficiency of a selective catalytic reduction (SCR) emissions control system fitted to a diesel engine in a typical bus, can fall dramatically when the engine idles – for instance, at a bus stop, at traffic lights or when caught in congestion. Professor John Preston says: “At normal road speeds, and where the engine is running under load, the SCR reaches its nominal operating temperature range and works as expected. But in the city centre, at bus stops and traffic lights the engine spends a lot of its time idling so the temperature of the catalyst falls, which reduces the NOx conversion efficiency to, in some cases, as low as 14%.”

The full findings will be published shortly, and further work is being undertaken looking at the potential for retrofitting insulation or even controlled heating around the SCR as a way of improving conversion efficiency in low load/low speed conditions encountered in city centres. So how can authorities improve the situation?

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Ricardo has launched a mobile vehicle emissions monitoring service.jpg
Ricardo has launched a mobile vehicle emissions monitoring service
Transport and mobility solutions research specialist TRL, highlights VW’s emissions test ‘cheat device’ as a pivotal event which has undermined public confidence in national and international authorities’ ability to improve air quality by imposing legislation on vehicle manufacturers. Contributors to one of TRL’s ‘Academies’ concluded that authorities in major urban centres needed to act and ‘take radical legislative steps and adopt new approaches to achieve step changes in air quality.’

While acknowledging a need for urgency, TRL warns “it’s important that sufficient base-line data is collected before the scheme is implemented.” For many authorities however, the first problem is identifying areas with poor air quality. While congestion and high traffic volumes are obvious indicators, the built environment, traffic management strategies and the vagaries of the wind confuse the situation. Fortunately, there are a number of services and products to help authorities identify and prioritise air quality problems.

Dynniq’s Virtual Emissions Monitor offers one way to identify pollution hotspots (see ITS International May/June 2016). The system profiles the traffic for vehicle type, count and speed and cross references the results with typical emissions for each vehicle and type to calculate the amount of pollution being discharged. Those figures are then fed into a 3D model of the area, along with the ambient weather conditions, to calculate the real-time air quality at street level.

Alternatively, Ricardo Energy & Environment’s new mobile vehicle emissions monitoring service can monitor locations of interest, to measure and record the emissions from each passing vehicle.


Using non-intrusive absorption spectroscopy, the system monitors and records emissions such as nitric oxide and nitrogen dioxide (NOx), particulate matter (PM), hydrocarbons, carbon monoxide (CO) and ammonia from the exhaust of passing vehicles. The system can measure emission from thousands of vehicles in a short space of time (without interfering with traffic flow) and uses ANPR to match the data to vehicle characteristics such as engine type and age.

This data can be used to identify the most polluting vehicle types (buses, heavy goods vehicles, vans and cars) and their respective contributions to emissions.

Early results allow a direct comparison between Euro 5 and Euro 6 engines in real-world driving conditions and the impact of ‘cold-starts’ on both petrol and diesel engine emissions in urban environments.

Parking equipment manufacturer Parkeon is also active in this area, offering an air quality data module option for its Strada parking terminal. This enables authorities to monitor emissions including PM and the greenhouse gas, carbon dioxide (CO2) at the roadside.

Having identified areas of poor air quality, the question then arises; what can be done to improve the situation? Back in 2003 TfL introduced a weekday (7am to 6pm) congestion charging zone in central London and five years later added a full-time low emission zone (covering most of the area within the M25 orbital motorway) for trucks, vans, 4x4s, buses and coaches. These ANPR-based schemes are not designed to prevent vehicles from entering London but the additional charges aim to deter drivers from doing so if not absolutely necessary.  

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In addition to the above, this October the current London mayor, Sadiq Khan, will implement a £10 toxicity charge on top of the £11.50 congestion charge and an ultra low emissions zone is planned for 2019 to target diesel vehicles.


The local authority covering much of central London, Westminster City Council, is also working on the air quality problem and aims to deter diesel car use by differentiating parking charges. A trial is currently underway at certain pay-to-park bays where the cost to park a diesel vehicle is 50% higher than for petrol-powered equivalents.

In the private sector, CitiPark is trialling emissions-based parking tariffs in central London using an APT Skidata machine at its Clipstone Street branch. Aimed at encouraging the use of low- or zero-emission vehicles, the technology sets individual parking tariffs according to vehicles’ CO2 emissions. ANPR cameras identify vehicles entering the car park and cross references the licence to a database listing CO2 emissions details, which are then automatically factored into calculating the correct tariff.

In CitiPark’s case, cars emitting 75g/km of CO2  and below qualify for 20% discount on the regular parking cost.

Traffic management strategies also have an impact on emissions and air quality. TRL’s Academy highlighted ‘dumb’ traffic lights, speed humps, chicanes and spot speed cameras as exacerbating both noise and emissions while ‘green waves’ and average speed enforcement can reduce environmental problems. And networked signals can also allow the creation of a ‘virtual cordon’ to hold vehicles outside poor air quality areas while providing free-flow conditions in the centre.

In the longer term, electric vehicles will mean much of the pollution creation (depending on how the electricity is generated) is moved away from urban areas. Volvo has already announced that from 2019 all its new models will feature electric motors – either as full electric or as hybrids.

City authorities in Sweden, Luxembourg, Belgium, China, the US and the UK are already deploying electric buses to improve air quality and reduce running costs and noise emissions.   

Volvo Buses says its 7900 Electric is up to 80% more fuel efficient than a diesel-powered counterpart. The 12m-long bus carries up to 83 passengers and its fuel efficiency comes from regenerative braking and almost zero ‘fuel’ usage when stationary at lights or as passengers board and alight.  

Roof-mounting the four relatively light lithium nickel manganese cobalt traction batteries allows a low floor for easy entry. A pantograph on the top of the bus connects with a contact pole for opportunity charging, which takes around six minutes and extends the length of route that can be covered.

Rather than selling its electric buses to transport operators, Volvo offers a turn-key solution to provide a defined, scheduled transport capacity at a specified cost-per-kilometre.

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