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The Noise indicator measures direct proximity to the highway network. To measure noise, the home is the point to measure the proximity to highway nuisance. Measuring proximity to highway noise involves creating a buffer, computing the catchment area and areas without noise, standardizing the percentage areas without noise in each census tract to the regional average, and standardizing the percentage of the area covered by the buffer in each census tract to the regional average.
Caltrans uses Hexagon (Intergraph) Geomedia software to support All Roads Network of Linear Referenced Data (ARNOLD) Linear Referencing System (LRS). The State Highway System (SHS) portion of ARNOLD is exported from Geomedia to ESRI ArcMAp to satisfy internal customer needs. The SHS LRS references a tabular Oracle database called the Transportation System Network (TSN) (Enterprise Oracle application).
This analysis uses the 2019 Transportation System Network (TSN) to create the half-mile buffer, determining whether people are impacted by highway noise. The TSN is used in many functional areas across Caltrans, and it is the base information system for all traffic safety analysis. Moreover, it maintains and links traffic census, collision, highway inventory data, and the most miles on the State Highway System (SHS).
Caltrans’ Linear Referencing System identifies the locations of features, events, and activities along with a transportation network. Although each data element has unique characteristics, they all must be referenced spatially by a geographic location. Some data elements are spatially referenced by actual coordinates (i.e., x and y) from GPS readings. However, most of this information is referenced by postmiles as described in the TSN.
Indicator Specific Method
A half-mile buffer was used to determine whether individuals were impacted by highway noise. This is a standard distance measure on which transportation environmental justice is designed. Research suggests that a half-mile distance is practical to analyze highway noise near underserved communities. The buffering approach is the simplest method to measure proximity because people within or covered by the buffer zone are close to the highway, thus, impacted by traffic noise.
The portions of the census tracts that intersected with the buffer are the portions of the census tract that were within a half-mile of a highway network and experience highway traffic noise. This buffer layer is used as an input layer to clip the “study area” shapefile, resulting in a layer in which the area of the buffer could be calculated for each census tract.
Rationale:
Highway traffic noise is one of the most damaging environmental nuisances for the population. Low-income people and minorities tend to live in areas with high road traffic noise. Studies have shown that children under 15 years old, people 65 years of age and over, with continued exposure to high road noise levels, can trigger many problems in their health and well-being. They are the most vulnerable groups affected by high road traffic nuisance levels.
Road traffic noise mitigation practices such as noise barriers have been constructed along highways that traverse residential areas, but the increasing traffic counts on those highways have diminished their effects. Considering the negative impacts of highway traffic noise on children under 15 years old, people 65 years of age and over, minorities, and low-income people, close attention should be paid to these population groups when undertaking transportation policies and investments.
Data Source(s): Caltrans Linear Referencing System (LRS) Database, Highway Performance Monitoring System (HPMS) Data (2019). California Public Road Data (PRD). Shapefile