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Table 2 Spearman correlations between frequency components of road noise levels and traffic flow rates

From: Road traffic noise frequency and prevalent hypertension in Taichung, Taiwan: A cross-sectional study

Vehicle type

Traffic flow number

Median (Q1-Q3) (vehicle/hr)

Correlation coefficients

Low frequency

Medium frequency

High frequency

31.5 Hz

63 Hz

125 Hz

250 Hz

500 Hz

1000 Hz

2000 Hz

4000 Hz

8000 Hz

MC

42

494 (280–704)

0.505a

0.594a

0.574a

0.488b

0.351c

0.279

0.312c

0.493a

0.395a

LDGV

42

600 (360–1032)

0.630a

0.592a

0.515a

0.356c

0.276

0.248

0.204

0.301

0.218

LDDT

42

138 (80–228)

0.398b

0.371c

0.491b

0.313c

0.110

0.162

0.147

0.132

0.093

HDDT

42

42 (24–80)

0.482b

0.539a

0.456b

0.350c

0.301

0.252

0.233

0.271

0.213

Total

42

1552 (764–2132)

0.601a

0.643a

0.586a

0.457b

0.331c

0.272

0.274

0.393c

0.340c

  1. HDDT = heavy-duty diesel trucks; LDDT = light-duty diesel trucks; LDGV = light-duty gasoline vehicles; MC = motorcycles; Q1 = first quartile; Q3 = third quartile. a P < 0.001. b P < 0.010. c P < 0.050.