|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.