Cambridge Environmental Research Consultants (CERC)

- Comprehensive Software for Modelling Road Traffic Pollution


The ADMS-Roads pollution model is a comprehensive tool for investigating air pollution problems due to networks of roads that may be in combination with industrial sites, for instance small towns or rural road networks. ADMS-Roads combines many of the scientific capabilities of CERC's air quality management system ADMS-Urban with an easy-to-use interface. Model operation is similar to other ADMS models, making it a simple task for anyone familiar with ADMS 5 to extend their modelling skills to cover road sources.

ADMS-Roads Extra is a specialised version of ADMS-Roads, which typically allows for more sources to be studied simultaneously. ADMS-Roads Extra essentially works identically to ADMS-Roads, unless stated otherwise in the ADMS-Roads description pages.

The ADMS models have been extensively used in local air quality management. ADMS-Urban, on which ADMS-Roads is based, is used across the world for air quality management and assessment studies of complex situations in towns, cities, motorways, counties and large industrial areas.

Here in the UK, over 70 local authorities used ADMS-Urban to help with their review and assessment and in developing air pollution action plans and remedial strategies. The ADMS models have also successfully been used for examining planning applications and EIA for proposed industrial, retail and domestic developments.

ADMS-Roads is currently used by a number of consultancies in the UK and abroad.

The science of ADMS-Roads is significantly more advanced than that of most other air dispersion models (such as CALINE, ISC and R91) in that it incorporates the latest understanding of the boundary layer structure, and goes beyond the simplistic Pasquill-Gifford stability categories method with explicit calculation of important parameters. The model uses advanced algorithms for the height-dependence of wind speed, turbulence and stability to produce improved predictions.

This diagram shows some of the possible inputs to and outputs from the model, and some of the modelling options available.

Many factors are important in predicting pollutant concentrations. ADMS-Roads has been developed with a number of features to simplify the modelling process and help users. For example:

  • Visualisation : ADMS-Roads has links to ArcGIS and MapInfo Professional GIS (Geographical Information System) packages as well as Surfer contour plotting package. The GIS link can be used to enter and display input data and display output, usually as colour contour plots.
  • Emissions inventory : Source and emissions data can be imported from a Microsoft Access database created by the user or exported from CERC's Emissions Inventory Toolkit, EMIT. EMIT contains current and future emission factors including those for vehicles, industrial processes and fuel consumption.
  • Emission factors : Defra's Emission Factor Toolkit emission factors.
  • Intelligent gridding : ADMS-Roads includes an intelligent gridding option which places extra output points in and adjacent to road sources to give excellent spatial resolution in areas of particular interest.
  • User-defined outputs : The user defines the pollutant, the averaging time (which may be an annual average or a shorter period), any percentiles and exceedence values that are of interest, and whether or not a rolling average is required. The output options are designed to be flexible to cater for the variety of air quality limits which can vary from country to country and over time.

In most cases, ADMS-Roads is first used to model the emissions from a base case scenario, that is, data (emissions, meteorology, background, etc.) are used to produce results that can be verified against locally monitored data from a recent previous year or the current year. Once the base case scenario has been validated, it is possible to investigate different scenarios, for example:

Impact of major development
ADMS-Roads is often used to compare air quality before and after major developments. An emissions inventory is compiled using the best available estimates for after the development. ADMS-Roads allows many What if? scenarios to be tried out, predicting concentrations at key receptors or across a wider area.

Future years
The majority of air quality limits are objectives for future years. These scenarios can be modelled in ADMS-Roads using Defra's Emission factor toolkit emission factors for future years, future predictions from EMIT or the user's own estimate. Likely changes in traffic flows, fleet compositions and background concentrations if known, can also be included in the future scenarios.

Traffic management
If the predictions for future years indicate that concentrations of certain pollutants are likely to exceed the objectives, it is usual to consider traffic management and emission reduction scenarios. For example, some local authorities in the UK are considering introducing Low Emission Zones within which only vehicles that have achieved a particular low-emission standard are allowed. The effect on air quality of introducing such measures can be investigated using ADMS-Roads. CERC's Emissions Inventory Toolkit, EMIT can be used for investigating the effect on emissions.

One of the most important advanced modules in ADMS-Roads is the chemistry module. The following options are available:

  • NOx – NO2 chemistry
  • Sulphate chemistry

Other advanced modules are:

  • Street canyons
  • Complex terrain

These modules are based on the latest understanding of the way these features affect the movement of airflow around the sources, and all have been shown to have considerable affect on observed concentrations.

Chemistry Module NOx – NO2chemistry

ADMS-Roads models NOx chemistry using the 8 reaction Generic Reaction Set (Venkatram et al., 1994) that includes reactions with ozone and hydrocarbons.

The NOx chemical reactions take place over a relatively short time period and in order to get accurate predictions of NO2 concentrations, NOx chemistry should be taken into account. The Generic Reaction Set predicts changes in ozone concentrations that are also of interest.

Sulphate Chemistry

The reactions between SO2 and other compounds in the air to produce particulates are based on those used in the EMEP model (Tsyro, 2001).

These reactions have a significant effect on the concentrations of particulates in areas where there are a large number of industrial sources emitting SO2.

Street Canyons

'Street canyons' are defined as the deep, narrow, valley-like spaces created when a road is enclosed by tall buildings on both sides. High pollution levels are often observed in street canyons. The street canyon module included within ADMS-Urban/Roads is based on the Danish Operational Street Pollution Model (OSPM, Hertel and Berkowicz, 1990, Hertel et al., 1990).

Complex Terrain

This module is based on FLOWSTAR advanced airflow model which calculates the change in mean flow and turbulence due to terrain and changes in surface roughness (land use).

Buildings (ADMS-Roads Extra only)

Users can include the effect of up to 10 dominant buildings on point source emissions. ADMS-Roads Extra creates an effective building for each point source from the user-defined buildings, and models the re-circulating flow in the lee of the building, the cavity region, as well as the building main wake.

ADMS-Urban and ADMS-Roads have been comprehensively verified in a large number of studies. This includes comparisons with data from the UK's Automatic Urban Network (AUN) during all of our consultancy studies and specific validation exercises using standard field, laboratory and numerical data sets.

CERC is also involved in European programmes on model harmonisation, and our models have been compared favourably against other EU and US EPA systems.

For further details of verification studies that have been carried out, please browser the Model validation page.

User Support

ADMS-Roads is supplied with an in-depth user guide (see the User Guides page) that details all user inputs and outputs, and includes a number of step-by-step worked examples.

Full details of the technical specification of ADMS-Roads can either be found in the Technical specifications page or on request from CERC.

An annual maintenance contract provides support for users; this includes:

  • maintenance model upgrades,
  • use of the helpdesk by e-mail, phone, fax or post,
  • attendance at the annual user group meetings,
  • newsletter twice a year, and
  • access to the password-protected user area.

CERC also offer basic and advanced training. Please browse our Training pages for more details.

If you would like any further information or to speak to one of our consultants about ADMS-Roads, please contact us.

Current versions and system requirements

Current software versions and release dates are listed here.

System requirements and compatibility with third-party software are described on the System requirements page.