NOISE & VIBRATION STUDY

General

The very nature of railway operations is such that there is potential for noise and vibration impact on areas nearby the railway line. For this reason, an investigation of the potential impact of noise and vibration from the proposed Gautrain Rapid Rail Link project was undertaken as part of the Gautrain Environmental Impact Assessment (EIA). The Noise and Vibration Specialist Study was an investigation into relevant issues during all phases of the project in an attempt to prevent and/or control noise and vibration during these phases. The specialist study covered potential air-borne noise as well as ground-borne noise and vibration which may result from the project and which can be addressed during the activities of the planning and design phase of the Gautrain as well as those for the construction and operational phases.

The proposed frequency of the Gautrain Rapid Rail Link during an average day has trains running at a minimum of 10 minutes headway in both directions. This further highlighted the need for a Noise and Vibration Specialist Study. The study was guided by the principles of the internationally accepted Integrated Environmental Management (EIM) process and the requirements of the South African Bureau of Standard’s codes of practice relevant to noise and vibration assessments. It was also undertaken in accordance with South Africa’s EIA regulations under the Environment Conservation Act.

Overall Findings

No major ground-borne noise and vibration impacts are predicted at the surface when the line is in tunnel. The noise and vibration limits set for the Gautrain will also not be exceeded along most of sections of the rail corridor. Where impacts may occur, mitigation measures such as sound barriers have been recommended.

Low frequency noise due to ground-borne vibration may possibly be audible in the area above the tunnel along the section in the area of the Parktown ridge. Methods to ease the impact are available and the bidders’ attention has been drawn to this matter.

The draft EIA report recommends average and maximum noise and vibration levels that must be observed where the Gautrain passes residential, educational and other noise sensitive areas. These levels (standards) are based on best international practice. Where necessary, mitigating measures will be implemented to ensure that noise and vibration levels are kept within acceptable limits. This will ensure that there is no damage to property and/or disruption to normal activities.

‘Worst case’ scenarios have been adopted in the study. There is thus a strong possibility that the real situation will be better than predicted. Even so, the successful bidder has to prepare a Noise and Vibration Mitigation Plan to manage and reduce foreseen noise and vibration problems.

The Air-borne Noise Impact Assessment

The intention of the Air-borne Noise Impact Assessment was to identify any potential problems and then to make recommendations to minimize potential air-borne noise impacts during the design, construction and operation of the Gautrain. In taking these aspects into consideration at an early stage, such a carefully designed, modern train will not only have reduced wayside, station and coach interior noise levels, but it will also produce less noise impact on the surrounding communities than other commuter trains operating in South Africa. Within these communities the following noise sensitive areas were defined for special mitigating measure attention:

• Outdoor noise areas such as parks, cemeteries and historical sites;
• Residences of single and multiple families; and
• Indoor noise areas including places of worship, libraries, educational facilities, hospitals, etc.

The study, which used international railway noise criteria, focussed on the immediate environments of the proposed railway up to a distance of 300 metres left and right of the centreline of the track. Other areas of potential noise, such as that generated by traffic accessing the stations, were also taken into consideration.

As an overall guideline, based on international standards, for a train passing by, the maximum daytime noise level proposed at the Gautrain railway reserve boundary is 85 decibels. The ambient (average) daytime level was set at 60 decibels. A railway reserve boundary is the interface between the reserve and the first row of impacted properties. The land use of the noise sensitive site must however also be taken into consideration and the appropriate maximum noise levels must be exceeded.

Findings of the Air-borne Noise Impact Assessment

At the time of the noise study, the average air-borne noise level in many of the areas along the planned rail corridors was already relatively high. This indicates that much of the area through which the Gautrain will pass is already significantly affected (degraded) by noise from urban activities, road, rail and air traffic as well as factory operations.

The Gautrain Rapid Rail Link has the potential for significant noise impact in the immediate environments along some sections of the railway lines, if not mitigated. The findings of the Noise and Vibration Specialist Study however show that the potential air-borne noise impact is of such a nature that appropriate measures can be taken to ensure that noise standards are not exceeded. The noise will furthermore reduce naturally with increasing distance from the line.

This scenario will be relevant during all the phases of the project although the impacts during the construction phases will be of relatively short duration. Air-borne noise impact in potential problem areas during the operational phase will be more permanent if not mitigated.

Ground-borne Noise and Vibration Impact Assessment

Human response to vibration is a complex and still developing field of study. Many countries, including South Africa, are only now realising the impact of vibration on humans. There are no official standards and impact assessment criteria in South Africa. International standards on how to assess human response to vibration are available but they do not include explicit vibration exposure limits.

The impact from ground-borne vibration from rail transit systems manifests in two main effects:

• Perceptible vibrations which are physically perceived by humans, or sometimes observable through secondary effects such as the rattling of windows.
• Low frequency noise – sound waves caused by ground-borne vibration which are perceived by the human ear as sound.

The ground-borne vibrations caused by rapid rail systems are initiated mainly by the interaction between the train’s wheels and the track. Vibrations are further influenced by variables such as the:

• speed of the train;
• condition of the wheels and track;
• construction of the track and tunnel;
• depth and geology of the soil;
• depth of tunnel and distance away from it; and
• type and construction of the building where the receiver of the vibration is positioned.

Areas of concern for this study included critical working areas such as hospitals and laboratories. Residential areas, offices, auditoriums and other noise sensitive activities were also considered. The ground-borne noise and vibration levels were calculated along the entire alignment of the track. In order to do this the speed of the train, the geology of the area and construction of the buildings on the surface were considered. In these calculations a conservative approach was taken which included that no vibration mitigation elements, such as resilient pads, will be installed between the track and the foundation. This enables the successful bidder to reduce the ground-borne noise and vibration impact where necessary by making use of appropriate track construction and tie-down methods.

The Gautrain’s Vibration and Ground-borne Noise Impact Assessment was mainly based on the methodology proposed by the US Department of Transport in the document ‘High-Speed Ground Transportation Noise and Vibration Impact Assessment’ of 1998. The impact criteria were set according to other standards such as the ISO Standard 2631, Guide for the evaluation of human exposure to whole body vibration.

Findings of the Vibration and Ground-borne Noise Impact Assessment (PDF-533KB)

The suggested alternative alignments for the Gautrain all have similar vibration impacts when the train is in tunnel, however, where the track is placed on surface the impact will be more significant.

It is probable that isolated areas along the Johannesburg and Pretoria corridor may be impacted by ground-borne noise and vibration emanating from the Gautrain project. The impact during the construction phase is more probable than that of the operational phase of the train.

Along most of the alignment where the track is in tunnel the ground-borne noise and vibration levels are predicted to be so low that it will not be perceived by the average human. In areas where the track is on surface the air-borne noise will dominate the impact.

During the construction phases of the Gautrain Rapid Rail Link, vibration impacts are highly probable directly above and adjacent to the proposed route. This will mainly be due to the drill and blast tunnelling operations. The impact can be lessened by selecting specific construction methods and limiting blasting events to specific times of the day.

Vibration and low frequency noise caused from the train when in operation will be permanent but limited to the immediate area above and adjacent to the track dependant on whether the track is respectively in tunnel or on surface. The nature and degree of the impact will be different according to whether the train is in tunnel, in cut or at grade. The impact can be alleviated by the initial design of the track bed and the track tie-down system, proper maintenance of the wheels and track as well as controlling the speed of the trains.