NPC Resources: Noise Increases with Vehicle Speed

Noise Increases with Vehicle Speed

When Congress allowed states to raise speed limits, and many states did raise speed limits from 55 mph to 65 mph and higher, highways in these states got noisier. The table below lists the change in the noise made by auotmobiles, medium trucks, and heavy trucks as they increase in speed from 30 mph to 70 mph. Raising the speed of an automobile 10 mph (from 55 to 65 mph) increases the noise made by that vehicle 3 dB, from 72 dB to 75 dB. Similarly, noise made by trucks increases from 86 to 88 dB with the same 10 mph increase in speed. In these examples, gas mileage also decreases by 15%.

The result is a substantial increase in noise for those living and working near highways. Soundwalls are capable of reducing noise levels by 10 dB, so increased speed limits have also significantly reduced the effectiveness of highway noise barriers.

Reducing speed limits on roadways and increasing enforcement of speed limits is often the most effective and cost efficient means of reducing noise. For example, reducing vehicle speeds from 40 to 30 mph is as effective as removing one half the vehicles from the roadway.

Speed (mph)	Noise at 50 ft (dB)
	Auto	Medium Truck	Heavy Truck
30	62	73	80
31	62	74	80
32	63	74	81
33	63	75	81
34	64	75	81
35	64	76	82
36	65	76	82
37	65	77	82
38	66	77	82
39	66	77	83
40	67	78	83
41	67	78	83
42	67	78	84
43	68	79	84
44	68	79	84
45	68	79	84
46	69	80	85
47	69	80	85
48	70	80	85
49	70	81	85
50	70	81	85
51	71	81	86
52	71	82	86
53	71	82	86
54	72	82	86
55	72	82	86
56	72	83	87
57	72	83	87
58	73	83	87
59	73	83	87
60	73	84	87
61	74	84	88
62	74	84	88
63	74	84	88
64	74	85	88
65	75	85	88
66	75	85	88
67	75	85	89
68	75	86	89
69	76	86	89
70	76	86	89
Source: Cowan, Environmental Acoustics, 150

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