Vd (7 am to 10 pm) and nighttime, Vn (10 pm to 7 am) traffic volumes of 317 and 28 vehicles per hour, respectively.
The project noise exposure levels for the Preferred Alternative are calculated below:
For the Category 2 receptors (Radisson Hotel and Youth Hostel), noise exposure in terms of Ldn at 50 ft was calculated as follows:
Leq (day) = SELref + 10 log (Vd) + Cs log(S/50 feet) – 35.6 = 47.7 dBA
Where SELref, the reference sound exposure level for automobiles and vans at 50 ft from roadway = 74 dBA (FTA, 2006); and
Cs, the Speed Constant for automobile and van pools = 30
Leq (night) = SELref + 10 log (Vn) + Cs log(S/50 feet) – 35.6 = 37.2 dBA
Ldn at 50 ft = 10 log [(15) x 10(Leq (day)/10) = 47.5 dBA
(9) x 10((Leq (night) + 10)/10)
] – 13.8
For the Category 3 receptor (St. Paul’s Episcopal Cathedral Church), noise exposure in terms of hourly Leq (h) at 50 ft was calculated as follows:
Leq (hour) = SELref + 10 log (V) + Cs log(S/50 feet) – 35.6 = 45.9 dBA
Noise impact is assessed based on a combination of the existing ambient noise exposure (LRRT) and the additional noise exposure (automobile traffic) that will be caused by the proposed project. Figure E-1 provides a handy graph that can be used to add sound levels in decibels. For example, if two sound levels of 64 dB and 60 dB are to be added, the difference in decibels between the two levels to be added is 4 dB. The curve intersects the “4” where the increment to be added to the higher level is “1.5.” Therefore the sum of the two levels is 65 dB.