Transit Accessibility Case Study: Orange Country, CA

Federal Highway Administration
The Orange County Transportation Authority (OCTA) provides transit service in a generally automobile-oriented part of southern California. Consequently, OCTA must plan its services and operations for maximum effectiveness and efficiency. To help with this challenge, OCTA has instituted a geographic information system (GIS) that provides detailed information on the demographic and land use characteristics of all locations throughout its service area. Examples are presented of how OCTA has used its GIS to enhance regional transit service planning. These GIS techniques can also be used for regional-level of analysis of transportation and land use policies. Techniques highlighted here include: Disaggregating socioeconomic data - Typically, population or employment density is assumed to be uniform across a census tract or traffic analysis zone. Yet in reality, the distribution may be very uneven. A GIS-based land use database can be used to refine estimates of the distribution of population or employment. The technique is applied in this case study for transit route planning and to measure transit accessibility. It could also be used for other applications in which the geographic distribution of impacts is important. One example is the overlay of unacceptable noise or air pollution levels on population data, as demonstrated in the SPARTACUS and Waterloo case studies. Determining transit accessibility - In transit planning, the service area of a transit stop or station is generally assumed to be a circle around the stop of one-quarter to one-half-mile radius. Yet not all of the streets within this circle can actually be reached within a walk of this distance, due to circuitous street patterns or physical barriers such as freeways. GIS-based network analysis can assist in identifying the streets that are within a given walking distance of a stop. In conjunction with population data, network analysis can be used to develop refined estimates of the population or employment served by a transit system. The results can be used 1) in service planning; 2) in measuring regional accessibility to transit; 3) to improve travel demand and ridership forecasting models; or 4) to identify areas in which pedestrian improvements may be required. In addition to describing these techniques and their applications, this case study describes the system, staff, and data resources that OCTA has utilized to develop its GIS.
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