Division 7 Community Outreach Soundwall Project

Ramon E. Nugent, P.E.A h IAcentech, Inc.

Carl RipaldiCarl RipaldiLos Angeles County Metropolitan Transit Authority

IntroductionIntroduction

• Bus Depot OverviewBus Depot Overview• Community Complaint History• Previous Actions Taken by MetroPrevious Actions Taken by Metro• Definition of Problem• Analysis• Analysis• Recommendations• Current Situation• Current Situation

Metro Division 7 Bus Depot – Looking SEMetro Division 7 Bus Depot Looking SE

Community ComplaintsCommunity Complaints

• Complaints from residences over several yearsp y• Residents for Quality of Life action group• Issues:Issues:

– Bus idling– Back-up alarms– Yard sweepers– Yard loudspeaker announcements– Maintenance operations– Vibration

Metro Noise Control ProcessMetro Noise Control Process

1. Metro installed an 8 ft block1. Metro installed an 8 ft block wallComplaints Continued

2. Metro added a 4 ft extension of plastic fencingplastic fencingComplaints Continued

3. Metro hired Acentech

Definition of ProblemDefinition of Problem

• Interview Div 7 OperationsInterview Div 7 Operations• Observe Div 7 bus operations• Interview residentsInterview residents• Develop hypothesis of sources of complaints• Measurement program• Measurement program

– Noise– VibrationVibration

• Analyze data

Definition of ProblemDefinition of Problem

• 240 buses at Div. 7240 buses at Div. 7• 200 buses “roll-out” - 3:30 a.m. and 7:10 a.m.• Six to twelve buses idling in the yardSix to twelve buses idling in the yard• 4 a.m. and 6:00 a.m., eight late-night buses

& 92 “Trippers ” return to the yard& 92 Trippers, return to the yard• Returning buses stop at the base of the ramp

before proceeding south to parking rowbe o e p oceed g sout to pa g o

Metro Division 7 Bus DepotMetro Division 7 Bus Depot

ley

Driv

eH

unt

Definition of Problem

Location d1 d2 d3 h1 h2 h3 h41 56 8 8 12 15 6 152 30 10 2 12 15 5 15

Definition of ProblemDefinition of Problem

Analysis – Field DataAnalysis Field Data

95

100L1@ Div 7

L10@ Div 7

85

90

A

Leq@ Div 7

L1@ 825

L10@ 825

Leq@ 825

L1@ 835

Bus Roll-out

Bus Roll-out

70

75

80

oise

Lev

el, d

BA L1@ 835

L10@ 835

Leq@ 835

60

65

70

No

50

55

13:

15:

17:

19:

21:

23: 1: 3: 5: 7: 9: 11:

13:

15:

17:

19:

21:

23: 1: 3: 5: 7: 9: 11:

13:

Hour

Analysis – Field DataAnalysis Field Data

• Noise levels at residences and at Div 7correlateNoise levels at residences and at Div 7correlate• Noisiest periods

– 9 a.m. to 11 a.m.9 a.m. to 11 a.m. – 7 p.m. to 9 p.m. (19:00 to 21:00)

• Highest noise does not correlate with bus roll outg• Highest noise occurs when buses return• Ldn = 62 to 63 dBALdn 62 to 63 dBA

Analysis - Returning BusesAnalysis Returning Buses

ley

Driv

eH

unt

Analysis - Bus Spectra 

25 Hz 50 Hz75

8014:15:16:17

125 Hz

65

70

17:18:19:20:21:22:

55

60

Leq,

dB

F

23:0:1:2:3:4:

45

50 5:6:7:8:9:10:

35

40

12.5 20

31.5 50 80 125

200

315

500

800

1250

2000

3150

5000

8000

q, d

BA

10:11:12:13:

Leq

1/3-Octave Band, Hz

Analysis: Wall – vs – Bus HeightsAnalysis: Wall vs Bus Heights

Wall Dimensions Engine Exhaust Height

11.5 ft8 ft

12 ft8 ft

ConclusionsConclusions

• Residential noise correlated with bus yard activitiesResidential noise correlated with bus yard activities• 1st story Ldn’s were between 60 dBA and 65 dBA• 2nd story Ldns were about 2 5 dB higher2 story Ldns were about 2.5 dB higher• Existing wall provided 11 to 12 dB reduction• Needed 4 decibel improvement• Needed 4 decibel improvement• Noise problem was in the 125 Hz octave band• Wall TL at low frequencies >22 dB• Wall TL at low frequencies >22 dB

RecommendationsRecommendations

• 16-ft wall16 ft wall• Surface density of at least a 4” solid CMU • Rated TL of at least 22 dB at 125 Hz 1/3-OctaveRated TL of at least 22 dB at 125 Hz 1/3-Octave

Band• Minimize backup alarms during early morning hoursMinimize backup alarms during early morning hours

– Bus parking– Forklifts– Maintenance vehicles

Current SituationCurrent Situation

• Built 16-ft+ wall built• No noise complaints• Residences and

Metro are Happy

Questions