The Hybrid Roadway Intersection Model (HYROAD) developed under this project is a computer program designed to predict the concentrations of carbon monoxide (CO) that occur near intersections. The model consists of three modules (traffic, emissions, and dispersion) and a graphical user interface. The model was designed to allow its practical use with minimal input from the user. When local information is not available, default inputs are specified for many variables allowing them to be bypassed if appropriate. Final agency versions of project deliverables have been distributed to the state DOTs on CRP-CD-32, Intersection Air Quality Model, NCHRP 25-6. Others may obtain copies by contacting the NCHRP or the TRB Bookstore. CRP-CD-32 contains agency versions of the final deliverables as follows: (1) Final Report, (2) Model Formulation Report, (3) User Guide, and (4) HYROAD (Version 1.1). A separate CD-ROM containing all project-related data is also available.

Passage of the Clean Air Act Amendments of 1990 required transportation agencies to assure that their actions did not create or exacerbate violations of ambient air quality standards. For carbon monoxide, these actions also had to reduce the severity and number of existing violations. Projects that did not conform could not proceed.

To demonstrate conformance with carbon monoxide (CO) standards, computer models are used to predict concentrations at hot spot locations either directly or indirectly affected by a project. Because CO concentrations tend to be highest near areas of heavy traffic congestion, signalized intersections in urban and suburban areas are often the focus of this modeling effort. However, a better understanding of emissions, dispersion, traffic, and their interrelationships was needed for more accurate predictions of CO concentrations at intersections. The research had to be national in scope and be coordinated with other relevant ongoing efforts.

Research resulted in: (1) an evaluation of information on intersection carbon monoxide concentrations and the pattern of monitored violations, the significance of modal emissions, and the current state of the practice in carbon monoxide intersection modeling; (2) an assessment of the suitability of existing intersection air quality models (emissions, dispersion, and traffic components); and (3) the development of an improved integrated model and a computer program for the air quality assessments of intersections at urban and suburban locations.