At the request of the Washington Department of Highways a comprehensive study was conducted of the exposures of toll collectors to carbon monoxide at the Evergreen Point Bridge spanning Lake Washington between Seattle and Bellevue.
The first phase of the study consisted of designing, installing and operating an automatic, continuous carbon monoxide monitoring system to establish typical air quality patterns in and around the toll booths.
The second phase consisted of developing a prototype toll booth positive ventilation system. Air, which is introduced through a vertical diffuser situated at one wall of the booth, travels horizontally across the booth and out the door. Parametric studies of sources and rates of ventilation air, diffuser design and other toll booth modifications were conducted in the laboratory. Subsequently these modifications were installed and investigated at an operating booth at the toll plaza. Concentrations of carbon monoxide in the collectors breathing zone were reduced to acceptable levels. Methodologies and results of these studies are described, and design recommendations for the control system are offered.