[Code of Federal Regulations]
[Title 23, Volume 1]
[Revised as of April 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 23CFR772.5]

[Page 397]
 
                           TITLE 23--HIGHWAYS
 
 CHAPTER I--FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION
 
PART 772_PROCEDURES FOR ABATEMENT OF HIGHWAY TRAFFIC NOISE AND 
CONSTRUCTION NOISE--Table of Contents
 
Sec. 772.5  Definitions.

    (a) Design year. The future year used to estimate the probable 
traffic volume for which a highway is designed. A time, 10 to 20 years, 
from the start of construction is usually used.
    (b) Existing noise levels. The noise, resulting from the natural and 
mechanical sources and human activity, considered to be usually present 
in a particular area.
    (c) L10. The sound level that is exceeded 10 percent of the time 
(the 90th percentile) for the period under consideration.
    (d) L10(h). The hourly value of L10.
    (e) Leq--the equivalent steady-state sound level which in a stated 
period of time contains the same acoustic energy as the time-varying 
sound level during the same time period.
    (f) Leq(h). The hourly value of Leq.
    (g) Traffic noise impacts. Impacts which occur when the predicted 
traffic noise levels approach or exceed the noise abatement criteria 
(Table 1), or when the predicted traffic noise levels substantially 
exceed the existing noise levels.
    (h) Type I projects. A proposed Federal or Federal-aid highway 
project for the construction of a highway on new location or the 
physical alteration of an existing highway which significantly changes 
either the horizonal or vertical alignment or increases the number of 
through-traffic lanes.
    (i) Type II projects. A proposed Federal or Federal-aid highway 
project for noise abatement on an existing highway.