As in many downtown areas in large metropolitan areas, air quality has been a serious concern in portland, oregon. Since the establishment of federal air quality standards in the early seventies, downtown portland has been in violation of the 8-hr carbon monoxide standard. But unlike most major metropolitan areas, portland has been willing to use parking management as a tool for improving air quality.As a central element of its transportation control plan, the city set a ceiling of roughly 40,000 parking spaces in the downtown and has maintained that ceiling for 13 yr. Although there is considerable optimism that the downtown will soon be in compliance with the carbon monoxide standard, there is also pressure to increase the parking ceiling to accommodate new growth in the downtown. This paper describes research conducted by cambridge systematics, inc., and the city of portland on alternative methods of reducing emissions in the downtown and on the "parking space equivalents" of these alternative measures. The 11 alternative measures that were considered have been referred to as "offsets" because they were viewed as potentially offsetting the air quality impacts of adding more parking downtown. The paper describes the 11 measures considered, the methodology used to evaluate the potential effectiveness of each in portland, and the conclusions reached about each as a potential offset measure. The project involved considerable quantitative research and modelling to estimate the emissions impacts of different types of parking behaviour and to estimate the emissions reduction potential of each measure. As a result, the paper provides new insights into the relationship between parking and air quality and can provide considerable guidance to other cities struggling to balance parking and emissions reduction needs.
Samenvatting