Constraints

General

In designing a noise mitigation measure for a particular situation, one has to consider a number of factors. Some of them are as follows:

	(a)	the amount of noise reduction provided by the noise mitigation measure;
	(b)	structural/foundation requirement of the noise mitigation measure require;
	(c)	land/space requirement of the noise mitigation measure;
	(d)	any obstruction to the use of road and pedestrian walkway caused by the noise mitigation measure;
	(e)	any potential hazard caused by the noise mitigation measures by obstructing or depriving enough emergency access, blocking drivers' view and so on;
	(f)	other undesirable effects caused by the noise mitigation measure, such as insufficient ventilation, loss of sunlight and so on;
	(g)	visual impact of the noise mitigation measure; and
	(h)	the capital and maintenance cost of the noise mitigation measure and how they compare with the same for other alternative measures.

In the next sections, we will look at some of the constraints on the use of noise barriers and noise enclosures and on the applicability of road resurfacing using low-noise materials.

Constraints on the Use of Noise Barriers and Enclosures

Some of the constraints are:

	(a)	The need to provide adequate emergency access as a crucial safety factor in densely populated or developed areas;
	(b)	The proposed barriers or enclosures should not obstruct the operation of emergency vehicles such as fire engines and ambulances or equipment and plant such as valves and fire hydrants;
	(c)	The proposed barriers or enclosures should not become a road hazard or reduce the degree of road safety in any respect;
	(d)	The need to avoid obstructing pedestrian flows or interfere with street-level activities such as loading and unloading, vehicular access to buildings, commercial and recreational activities;
	(e)	Ease of maintenance;
	(f)	Disruption to traffic;
	(g)	Loss of road space;
	(h)	Degradation of air quality;
	(i)	Structural requirements;
	(j)	Loss of sunlight;
	(k)	Landscape impact; and
	(l)	Visual impact.

Constraints on the Use of Open-Textured Road Surfacing for Existing Roads

The use of road surface made of open-textured material instead of a brushed concrete one may help to ease impact of traffic noise by reducing noise from road/tyre interaction. For a quick review of the principle and application, please click here.

But an open-textured road surface is only effective under the following circumstances :

	(a)	The road should be originally be paved with brushed concrete or other similar non-open textured suface.
	(b)	Traffic noise from the road is the dominant noise sources. For example, highway will be preferable.
	(c)	Flat roads are best because slopes take too much force from vehicles braking and climbing for the less-solid road surface to withstand. As such, local roads with sharp bend would not give satisfactory result. Open-textured road surface gives the best result in reducing noise on flat road with smooth high-speed traffic because of the domination of road/type noise.
	(d)	Fewer heavy vehicles would also be preferable because engine noise, instead of road/type noise, will dominate with the increase of heavy vehicle proportion.