Evaluating Air Quality Impacts of Transit Service Improvements



Evaluating Air Quality Impacts of Transit Service Improvements

Authors

SUTTON J C, GIS/Trans, USA

Description

Orange County in Southern California is one of the fastest growing counties in the USA. Between 1994 and 2020 population is forecast to increase from 2.59 million to 3.25 million (25% growth) and employment from 1.26 million to 2.12 million (68% growth).

Abstract

Orange County in Southern California is one of the fastest growing counties in the USA. Between 1994 and 2020 population is forecast to increase from 2.59 million to 3.25 million (25% growth) and employment from 1.26 million to 2.12 million (68% growth).

Similar to other rapidly growing suburban areas, Orange County faces the challenge of providing transit service in a setting predominantly designed for automobiles. This is especially the case in the expanding cities of South Orange County that are held up as archetypes of so Called "edge cities". This study arose out of a desire by the Orange County Transportation Authority (OCTA) to better understand the relationship of land use patterns and densities to the demand for transit and air quality impacts. It was anticipated that at a minimum such analysis would help with local level planning for bus stop location and bus routing; and direct policy toward actions that are likely to mitigate deteriorating air quahty.

From a transit-oriented design perspective the county can be divided into three areas (Figure 1).

* North area contains "older" cities with well-established bus routes and the highest number of transit trips.

* Central area is a mixture of new and traditional cities with fewer transit riders and more segregated land uses that are less transit-friendly.

* South area has the newest cities, apart from some coastal commtmities, where most of the new development is occurringl These new cities have yet t o establish anything more than basic transit service and are therefore open to transit-oriented design if applicable.

Empirical data from Orange County confirm that more than 80 percent of bus riders walk from their trip origins to bus stops, and 90 percent of riders walk to their final destination.

From OCTA's 1990 on-board survey more than 80 percent of bus riders said they would walk up to 1Ú4 mile to and from bus stops. Transit trips account for less than 3% of all motorized trips and at the time of this study averaged about 55,000 riders per day. Even in the older cities that are more transit-friendly bus ridership rarely exceeds 6% of total trips. Nevertheless, OCTA provides a comprehensive range of bus services (more than 60 bus routes) supplemented by other local city bus operators. As described later, OCTA's efforts in restructuring bus services to improve access and levels of service have resulted in average ridership increasing to 65,000 per day, a significant improvement.

The air quality impact analysis is part of a larger project to develop a GIS based Transit System Analysis Model (TSAM) that has capabilities to evaluate route restructuring and other transit service changes. The focus of this paper is on evaluating air quality impacts and how this is accomplished by integrating disparate data sources from census, surveys, and model results. However, in order to provide context for the air quality analysis a brief description of TSAM and its development is presented below.

Publisher

Association for European Transport