|Type I barriers||Type II barriers||All other types|
NOTES: Forty-five miles of barriers, while assigned a year of construction, cannot be assigned a cost. California did not provide data for the years 1999-2004, and therefore these years may not be comparable with previous years.
A Type I barrier is built on a new highway project or a physically altered existing highway.
A Type II barrier is built to abate noise along an existing highway (often referred to as retrofit abatement) and is not mandatory.
All other types of barriers are nonfederally funded.
SOURCE: U.S. Department of Transportation, Federal Highway Administration, Office of Environment and Planning, Highway Traffic Noise Barrier Construction Trends (Washington, DC: May 2006), tables 1 and 3 as reported in U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics, table 4-52, available at http://www.bts.gov/publications/national_transportation_statistics/ as of October 2008.