Emissions

Emissions and Greenhouse Gases.

Understanding the environmental impacts of roadway management strategies is essential not only to the estimation of construction cost, but also the protection of the environment and the conservation of the global ecological system. Vehicle speed and fuel consumptions may vary with driving conditions. Vehicle emissions can be estimated based on the speed, acceleration rate, and Vehicle Specific Power (VSP), which could normally be listed in an Operating Mode Identification (OMID) table. The relationships between pavement roughness (indicated by International Roughness Index or IRI) and speed/fuel consumption could be reflected by linear models, while the IRI is nonlinearly correlated to the emissions. It is recommended further identifying the relationships between IRI and emissions with more on-road tests for all types of vehicles on different types of roadway systems, so as to minimize the environmental, ecological, and even public health impacts through proper roadway management strategies.

The current work being undertaken for the Ministry of Transport, focuses on the effects of road transport on aquatic ecosystems and by default is concerned with the contaminants and their loads generated by motor vehicles. All of the stormwater quality models that are commonly in use deal with the overall loads produced by all activities within urban areas. This report focuses on three aspects of the information required by the VFEM-W. These aspects are those that provide the framework for the emissions hub within the model (refer Figure. 1.1). The
cells for any given source within the hub contain three key pieces of information that allow emissions of contaminants to be calculated over time within a given section of roadway. These are:

  • The concentration of contaminant present. 
  • The rate that the contaminant is released by an individual motor-vehicle.\\\\
  • The rate at which the emission from a particular source is deposited to the road surface and is then available for stormwater transport.

A wide range of contaminants are emitted from motor vehicles. Typically estimates of emissions are only required for those contaminants whose discharge to the environment is of environmental significance. The focus of this report is for those key sources known to contribute contaminants and those contaminants identified as being of potential environmental concern (COPC). Typically the COPC include the USEPA priority inorganic and organic pollutants in addition to a range of motor vehicle specific organic compounds. However where data is available on other significant contaminants in emissions from motor vehicles it is identified in this document.

The report presents information on the emissions from motor vehicles in seven sections:

  • Section 2 provides an overview of the vehicle fleet and how it is categorised and how VFEM-W handles vehicle types and some of the core factors that influence emissions.
  • Section 3 provides information about emissions from brake systems.
  • Section 4 presents information about emissions from motor vehicle tyres.
  • Section 5 presents information about emissions of lubricants and greases.
  • Section 6 provides information about emissions of coolants.
  • Section 7 provides information about the emissions from vehicle exhaust systems and includes specific discussion on the emission of contaminants from vehicles with catalytic converters.
  • Section 8 examines the wear of material from bitumen road surfaces.

In each of these sections information is presented on the contaminants present in that source and the available information on emission rates for that source. Finally in Section 9 information is presented in relation to the pathway from the source to the road surface, as not all of the emitted contaminant is likely to end up on the road surface and then be available for stormwater transport to a fresh or coastal receiving environment. Factors are identified that provide a first estimate of air to road deposition.

Paper proposing modelling of vehicle emissions. This formed the basis for the model implemented in HDM-4.