24 C O N T E X T 1 4 4 : M A Y 2 0 1 6 the village of Norton,Worcestershire, and a town house in the city of Bath. Taken as a whole, the eight case studies contained in the two reports simply do not fully support the report’s conclusion that HGV traffic vibration was not a factor in the structural damage caused to these buildings. In purely statistical terms, 25 per cent of the structural engineers’ reports agreed that traffic-induced, ground-borne vibrations would ‘affect buildings’ and that ‘vibration will be a possible cause of damage’ and might ‘exacerbate the already damaged areas’. A further 25 per cent of the engineers’ reports stated that, on the evidence presented, the case for groundborne vibrations causing damage to historic buildings was neither proved nor disproved, and suggested the need for further testing and monitoring. Therefore while the conclusions of the two reports may have been factually correct in stating that there was no ‘direct evidence’ for ground-borne vibrations being the direct cause of major structural damage to historic buildings, a far better reflection of the engineers reports would be the conclusion that, based on the findings presented in the case studies, there was insufficient evidence to make a firm judgement either way – and that further detailed study was required before the matter could be determined. This statement, that more detailed study was needed before any firm conclusion was drawn, was further strengthened by the additional information contained in the third report. As well as detailing the results of the two earlier reports, TRRL Research Report 246 also contained a short summary of a review of data of vibration damage in heritage buildings. This review, undertaken under contract by Brian Morton and Partners, involved approaching over 500 individuals and organisations across the world requesting information on possible cases of damage to historic buildings that could be attributed to traffic vibrations. The survey also investigated the claims made in earlier decades (Crockett, 1973) that ecclesiastical buildings subject to heavy vehicle vibrations showed structural damage as a result. The results of this survey were largely inconclusive. While there were a number of cases where it was claimed that traffic vibration was responsible for structural damage, definitive data was unavailable, and the survey results described the claims as unsubstantiated. There were only two specific cases where traffic vibrations were deemed to be having a direct and negative effect on the structures. However, in both cases the report concluded that the structural damage was the result of site-specific conditions.The report concluded that ‘there were many studies where vibration was thought to be a possible cause of damage either directly or in combination with other factors but no evidence was available to confirm or deny these impressions’. What the actual data from all three reports makes clear is that the oft-quoted conclusions were not a true and accurate reflection of the survey work undertaken, or of the views of those professionals who undertook the work. The majority of their individual conclusions, taken across the physical surveys and the examination of the anecdotal evidence, were that, in certain specific cases and circumstances, HGV vibrations did cause damage to historic buildings. In most of the other cases they could neither confirm or deny the suggestion, and consistently suggested that further study was required before drawing any meaningful conclusions. Since these reports were compiled over quarter of a century ago there have also been a number of other changes that call into question the validity and continuing relevance of the 1980s tests.The most significant of these is undoubtedly the increase in the maximum permitted weight of HGVs on roads in the UK. At the time of the initial surveys the majority of HGVs on UK roads still conformed to the pre-1982 maximum weight of 32.5 tonnes. The surveys were undertaken at a period of transition, subsequent to the new 38-tonne limit being introduced in November 1982, but before many road hauliers had upgraded and enlarged their transport fleets. Since that time there have been two further increases: from 38 tonnes to 40 tonnes in 1999, and increased again to 44 tonnes in 2001, representing an overall increase since the time of the initial surveys of more than 35 per cent.While it was argued that a larger maximum weight limit would result in few individual vehicle movements, this has also proved not to be the case.There has been an overall increase in vehicle movements in each decade since the original surveys were undertaken. In effect, the situation is now that historic buildings are subject to an increased number of vehicle movements by larger and heavier multi-axle vehicles. It is becoming increasingly clear that a number of historic building specialists no longer place a great deal of faith in the current guidance. In a number of key projects and decision making processes local planning authorities have chosen to set aside the current advice, and have implemented specific projects and policies based on the belief that traffic-induced ground-borne vibrations are a significant factor in causing damage to historic buildings. The whole city of Bath has been a world heritage site since 1987, recognised as a place of outstanding universal value for its architecture, town planning, landscape and archaeological remains, and for its role as a setting for social history. However, the popularity of the city has resulted in heavy congestion within the city centre and a large number of HGVs travelling through its streets. According to the world heritage site management plan, adopted by the city authorities in 2012, ‘Traffic can intrude on the enjoyment of sites, damage the built fabric, inhibit free movement of pedestrians and create pollution. Air pollution and the weight and vibration of the vehicles are threats to those who live in Bath and visit it, and to the historic buildings, townscape and landscape’ (City of BathWorld Heritage Site Management Plan, 2012). In 2007 the council worked with four other historic European cities to submit a bid to the European Commission’s CIVITAS Plus programme.The successful bid secured €3.975 million to implement new transport options in Bath.The four-year programme, which began
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