Developing a holistic tranquillity assessment method from a sound- scape design approach Adam Thomas 1 Arup 10th Floor, The Plaza, 100 Old Hall Street, Liverpool, United Kingdom, L3 9QJ. David Owen 2 Arup 8 Fitzroy Street, London, W1T 4BJ, United Kingdom. Sarah Drysdale 3 Arup 8 Fitzroy Street, London, W1T 4BJ, United Kingdom.

ABSTRACT Standardised soundscape methodologies are now being commonly applied to measure and in- terpret the perception of acoustic environments, in context. Different tranquillity assessments exist that make use of objective measurements of sound levels, interpretation of the sound sources present, and visual features in the surroundings. These have been shown to work well but with the advancements in soundscape research is it possible to improve or supplement these methodologies through the addition of a specific soundscape assessment oof the tranquillity of a space? Using the data collection methods of soundscape principals defined in ISO 12913-2:2018 the proposition was to develop a supplementary assessment method for small urban spaces that could be valued for their tranquillity by local communities and individuals. The method considered existing research on Attention Restorative Theory and optimum tran- quil spaces to identify a set of perceptual variables, or attributes, for use during a ‘Tranquillity Soundwalk’ in a related questionnaire. The methodology was tested by the authors as a pilot study by conducting a Soundwalk at a set of heritage locations within the Knowledge Quarter of London. The findings are supportive with recommendations for further development of the method that should be tested with a statistically significant sample of participants.

1 adam.thomas@arup.com

2 david.owen@arup.com

3 sarah.drysdale@arup.com

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1. INTRODUCTION

The health and wellbeing benefits of providing restorative environments for communities and indi- viduals is well understood. Hartig, Mang & Evans (1991), Ullrich (1991), Abkar et al (2010) and Kuo (2010) all give evidence demonstrating that natural tranquil surroundings have profound beneficial physiological effects on people’s health and wellbeing. Furthermore, Pheasant et al (2009) believed that the restorative urban environment, which help people to escape stress of modern urban living, are more important than rural tranquil space for the nation’s wellbeing. This is ratified by the signif- icant urban expansion of modern times. The UN Department of Economic and Social Affairs predicts that it will exceed 6.5 billion by 2050. This seismic expansion puts pressure on all land space in urban environments, as the requirements for urban housing increase. The importance of urban settings that can provide such restorative effect through respite is now being recognised by policymakers and planning authorities. They hold an increasing responsibility to pro- tect and enhance ‘ tranquil places ’ that serve the wellbeing of local communities.

1.1. Literature interpretation In the field of psychology, tranquillity has been defined as ‘how much you think this setting is a quiet, peaceful place, a good place to get away from everyday life’ emphasizing the restorative effect of a certain place or set-up (Herzog and Bosley, 1992). A number of research projects tranquillity have been completed by government bodies. The Civil Aviation (ERCD Report 1207) authority provides ‘the quality or state of being tranquil; calmness; serenity, a disposition free from stress or emotion and a state of peace and quiet’. The Campaign to Protect Rural England (2006) provides ‘the quality of calm experienced in places with mainly natural features and activities, free from disturbance from manmade ones’. The Welsh Government (2012) provides an expanded definition in comparison to other: provides ‘An untroubled state, which is peaceful, calm and free from unwanted disturbances. This can refer to a state of mind or a particular environment. Tranquillity can be measured in terms of the absence of unwanted intrusions, or by a balancing of positive and negative factors. These include the presence of nature, feeling safe, visually pleasing surroundings and a relaxing atmosphere.” This definition combines both the engagement with the environment, the state of one’s mind and the avoidance (instead of absence) of human intrusions and arguably provides the most detailed definition that could be used for the purposes of assessment. Whilst none of these definitions are exactly alike, when reviewing definitions four common qualita- tive themes were found to prevail: • a personal quality or state of mind; • calmness; • the absence of human intrusion, free from disturbance; and • human focus on natural, or contextual, features.

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2.2 Policy inclusion and interpretation The White Paper, The Natural Choice: Securing the Value of Nature 2011 committed the UK Gov- ernment to “work with local authorities to establish mechanisms for formally identifying and protect- ing urban quiet areas, so that people living in cities can benefit from access to areas of relative quiet for relaxation and contemplation”. Following the publication of the White Paper, the UK government published the National Planning Policy Framework (NPPF) 2012, introducing Local Green Space designation, which permits a local authority to protect spaces close to the community with particular local significance, beauty, historical significance, recreational value, tranquillity or richness of its wildlife. The most recent update to NPPF is even more specific in defining tranquillity and what elements of the soundscape that should be protected. It states that: “For an area to justify being protected for its tranquillity, it is likely to be relatively undisturbed by noise from human sources that undermine the intrinsic character of the area. It may, for example, provide a sense of peace and quiet or a positive soundscape where natural sounds such as birdsong or flowing water are more prominent than background noise, e.g. from transport.” The inclusion of the term soundscape, and the phrase ‘sense of peace and quiet’ indicate that the perceptual qualities of a location in its surroundings is as important as the objective measurements that are historically used in acoustic assessment. The Rural White Paper, Our Countryside: The Future – A fair deal for rural England (DEFRA 2000), acknowledges the value of the countryside as a recreational resource. The paper acknowledges the importance of tranquillity alongside other perceptual characteristics by stating “It is not just its phys- ical features which gives the countryside its unique character; there are also less tangible features such as tranquillity and lack of noise and visual intrusion, dark skies and remoteness from the visible impact of civilisation. ” Tranquillity is mentioned in the National Planning Policy Framework (NPPF, 2012) under two sec- tions: ‘Promoting Healthy Communities’ (paragraphs 76 and 77) and ‘Conserving and Enhancing the Natural Environment’ (paragraph 123). In the NPPF, the concept of tranquillity is closely correlated to the landscape (local green space) and it is acknowledged that by protecting important green areas and restricting noise, tranquillity is maintained. Also, in the NPPF, tranquil spaces are not restricted to quiet places, but also include visual aspects such as the intrusion of man-made structures into a perceived natural landscape. 2. LITERATURE

Two significant studies from environmental psychology are summarised here. The construct of soundscape, and a summary of its established assessment methods, are provided in section 2.3. 2.1. Attention Restorative Theory Kaplan & Kaplan (1989) emphasized the significance of natural environment in restoration of human being in the modern life in Attention Restorative Theory (ART). The basis of ART is that exposure to nature is not only enjoyable but can also help us improve our focus and ability to concentrate. Payne (2008 and 2010) explored how the soundscapes of urban parks and other places can provide restora- tive effect by applying this theory to more urban contexts. The basis of ART is that there are four proposed cogitative states, or states of attention, along the way to restoration (Kaplan & Kaplan

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1989). These are fascination, being-away, compatibility and extent (being made up of scope and co- herence). The utilization and application of ART to restorative soundscapes has been extensively explored by Payne (2008, 2010 & 2013). The four cogitative components listed above are broken down and ex- plored in detail to provide 19 Perceived Restorativeness Soundscape Scale items between these cog- nitive groups. This work provides precedence in the of ART cogitative components being applied as perceptual attributes. Here attributes are defined as a 2perceptable characteristic2 (ISO 5492 (2008). 2.2. Optimum tranquil spaces In the field of optimum ‘tranquil space’ Herzog & Bosley (1992) provides five informational de- scriptors. These are mystery, focus, coherence, unstructured openness and surface calmness. Herzog and Bosley’s work is based upon visual data, mainly of natural rural landscapes but they do explicitly mention that “Whilst the last two [coherence, unstructured openness] are useful in understanding how wider views of the rural landscape are interpreted, mystery, focus and coherence are particu- larly useful when attempting to interpret urban environments. ” 2.3. Soundscape assessments. Soundscape is defined in ISO 12913-1:2014 as “ an acoustic environment as perceived and experi- enced and/or understood by a person or people, in context ”. Part two of the ISO series (ISO 12913- 2:2018) provides three methods of data capture that can be used to assess soundscapes. These are: • Gathering participant responses through a survey questionnaire (either in-situ or where sound is reproduced by headphones or loudspeakers); • Gathering participant responses through a guided soundwalk where the investigator is present and able to gain an enhanced understanding of the locations features and context; and • Gathering responses through guided interviews to explore associations, feelings and emotions more deeply. In addition to the participants self-reported perceptual responses, when in-situ responses are gathered through a questionaiirre or a soundwalk, high quality audio and visual data is simultaneously cap- tured. The minimum requirements of soundscape data capture are set out in Appendix A of ISO 12913- 2:2018 and include; the selection and classification of participants; the characterisation of the studied acoustic environment (including sound source composition, sound level metrics and details on the location and conditions); and the human perceptual response data from participants. Informative examples are provided in Appendix C which include questionnaire structure and exam- ples. A set of attributes (perceptual variables) are provided that are taken from the circumplex model that has been applied to soundscape research by Axelsson (2010). This circumplex is based upon a dimensional model of emotion theory which can be traced back as late as Wundt in the 19 th Century. Russel (1981) provided a circumplex model of affective states elicited by environments using a 2D bipolar space based on pleasure/displeasure and arousal/sleep which has been given a lot of empirical support. A recent and efficient account of this history is provided by Fiebig (2020).

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4. ASSESSMENT METHODS

Three developed assessment methods that are applied to environmental assessments of tranquillity are outlined below. In each case, the prediction method is based predominantly on objective data. They are summarized only briefly here, with the intent of providing an understanding how sound- scape methods could be used to complement and enhance these existing applied methodologies, in order to meet any future policy needs that are expected to contain stronger reference to the importance of soundscapes in assessment. 4.1. NPPF In the context of Environmental Impact Assessments, tranquillity is typically assessed by landscape professionals who refer NPPF. This type of assessment is typical for large scale infrastructure schemes have the potential to impact on rural settings, particularly where an effect is potential within an Area of Outstanding Natural Beauty (AONB). One example of this approach, is The Campaign for Rural England produced “Tranquillity Map for England” (2006) which was then followed by “Tranquillity Mapping: Developing a Robust Method- ology for Planning Support” (2008). These are large scale methods that provide maps of tranquillity on a national scale. The mapping is aimed at the protection and enhancement of rural areas and works at a grid resolution of squares covering 500m x 500m areas with an individual tranquillity scoring. Whilst this is no doubt an excellent resource for large scale assessments for infrastructure schemes it is not possible to apply the mapping to the urban setting where, as discussed above, smaller locations have been reported to provide value for their tranquillity by individuals and communities. 4.2. The University of Bradford Method The method known as The University of Bradford Method predicts perceived tranquillity as a com- bination of two factors: the level of man-made noise (based on road traffic noise level) and the per- centage of natural and contextual features (NCF) in the visual scene. Considerable work has been completed to refine, develop and validate this procedure by Watts and Pheasant (2013), Watts and Pheasant (2015) & Watts and Marafa (2017). The method provides a very easy to implement proce- dure using noise level data from road traffic and visual imagery. 4.3. The Natural Tranquillity Method The Natural Tranquillity Method derived by Bentley (2019) originally aimed to build on The Univer- sity of Bradford Method but following some extensive fieldwork research, a new method was derived that was non-linear, removed the NCF and included three new parameters; Percentage Only Natural Sound (PONS), Natural-Man Made (NAMM), and a correction for the amount of noise from road and rail sources. 5. SOUNDSCAPE METHOD

The concept of a Soundwalk has been around for over 40 years and its method has been applied to many different uses. The soundwalk method (ISO 12913-2:2018) provides a structured soundscape data collection methodology. Two significant benefits of the soundwalk method when assessing an environment are:

1. The experience can be curated to suit the needs of the assessment in the context of a design

project with a related research question; and

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2. The method provides an ecologically valid data collection environment where self-reported

responses can be gathered in situ. The first point is an important practicality when working to assess a specific location or design inter- vention. The second point provides an improved data set. Not only because of the ecological validity of the visit to the location by participants, but also because instantaneous self-report measure- ments are barely influenced by memory distortions. Gärling et al. (2020) 5.1 Pilot Soundwalk A pilot soundwalk was undertaken by the research team to test the process of gathering data on peo- ple’s perceived tranquillity and any perceived restorative effect, based upon the data capture methods defined in ISO 12913-2:2018. Unfortunately, the pilot was not sufficiently large to provide a robust data set, but the process was evaluated and the data capture method for a future more rigorous tran- quillity assessment improved. The future study shall be conducted with a statistically significant num- ber of participants; made up from local exports and potentially project stakeholders. The pilot soundwalk test data collection method aimed to:

1. Curate a Soundwalk with a small group of subject matter experts across a number of known

and pre-chosen sites that feature historical assets or heritage features that may be valued for their perceived tranquillity or restorative effect; 2. Achieve the minimum requirements of soundscape data capture as detailed in ISO 12313-2; 3. Capture data at each location on participants perceived ‘tranquillity’ and ‘restorative effect’; 4. Capture data from participants on a set of perceptual attributes that are derived from the re-

viewed research strands of Restorative Attention Theory, and the literature on optimum tran- quil spaces; 5. Evaluate the data collection process within the group to identify any strengths and weaknesses

within the method for further development; 6. Review responses to explore potential relationships between the standard soundscape circum-

plex and the perceived ‘tranquillity’ and ‘restorative effect’; and 7. Explore the use of a set of perceptual attributes that relate to the Cogitative components from

Attention Restorative Theory research; and/or the environment psychology concepts from Optimum Tranquil Spaces research. An example of the questionnaire used on the pilot can be found here . Stereo audio recordings and sound level measurements were made alongside still photography to document the conditions at each location. This was deemed as being satisfactory to provide the audio-visual references to each loca- tion for the pilot study. 6. DISCUSSION

Following the pilot soundwalk test a ‘lessons learnt’ reflective session was held with the participants and test co-ordination team to discuss and evaluate the process and responses, which are summarized in the following sections.

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6.1. Tranquillity and emotion theory The comparison of a set of agreed tranquillity attributes to the dimensional circumplex model (Axel- son, 2010) is useful. This allows for comparison of the discrete set of perceived tranquillity attributes against a widely used and well understood dimensional model. Whist direct comparisons of the tranquillity data cannot be made to other soundscape surveys, it is deemed to be potentially useful to use circumplex results to consider the locations assessed against other soundscape data and contexts. Calmness is an obvious dimension where similarities were no- ticed even in the small number of results obtained during the test pilot. Further work could explore how tranquillity attributes could be incorporated better into a dimensional model. 6.2. Quantitative and qualitative data The collection of quantitative perceptual data using the attributes defined provides a useful, and fast method of interpretating data from the field. The questions that asked for text responses resulted in either single word responses or passages of text. In terms of streamlining the process so that it can more easily and efficiently be applied to project work within the built environment it may be better to limit the qualitative responses to people providing several single words that they feel represents the participants responses to the soundscapes experienced. This will not provide as deep and rich data that can be gathered through purely qualitative means, but it was found that participants were incon- sistent in what they wrote in these sections and there was a general need to shorten the questionnaire process to control the timing of the activity. More detailed qualitative data could be gathered as required through guided interview techniques later, possibly using the immersive audio-visual stimuli to reproduce the soundscape in a laboratory environment. 6.3. Misattribution Misattribution, defined as people mis-interpretating or mis-understanding the attribute and their def- initions used in a study, is considered to be the biggest risk to the perceptual data collection of the exercise. The survey team had undergone some attribute training prior to the soundwalk but even after this training several participants struggled to interpret the attribute in relation to the attribute description and comfortably rate their own response in situ. Attributes that were found to be particularly difficult were mystery, compatibility, coherence and extent. Since the pilot was completed some further reading on the origin of these components has been completed. Kaplan & Kaplan (1989) do suggest that the variables used in Attention Restorative Theory can be categorised into ‘comprehension variables’ and ‘exploration variables’. This division may be useful in determining a single set of attributes that can be used for the tranquillity soundwalk assessment method. Another comment from the lessons learnt session was that there were woo many of them and the distinction between some attributes was hard to determine. For example, coherence and compatibility. More work is required to understand and better define a set of tranquillity attrib- utes that can be easily interpretated and are distinct in their meaning and contribution to the tranquil- lity of an environment. Additionally, it would be useful to explore the importance of attributes and if any weightings should be applied to ascertain their importance in overall contribution to the perceived tranquillity of a location and context.

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6.4. Pilot soundwalk results The Pilot Soundwalk results generally align with calculated predictions of tranquillity rating using the TRAT tool and the Natural Tranquillity Method. There is also general agreement between the results of places providing a restorative effect and being perceived as Tranquillity. Whilst this is not surprising it does seem to provide some evidence that the use of Attention Restorative Theory attrib- utes are promising. The results are not published here as they only represent a snapshot of the potential perception of the locations and a more detailed study is required. 7. CONCLUSION

Tranquillity defined usually include perception-based qualities which are less tangible and so difficult to measure objectively. The growing field of soundscape research provides assessment methods of human perception of environments that could be useful in adding context to the assessment of tran- quillity. Literature related to soundscape and restorative environments features cogitative states or qualities that could be developed into a set of perceptual attributes. This is explored through the development of a soundwalk questionnaire which was tested as a pilot study. The method shows promise in potentially supplementing and enhancing the existing objective assessment methods. Recommendations are to simplify the questionnaire to improve the data capture quality and for the exercise be repeated at scale with a larger number of participants where objective measurements are made to determine tranquillity predictions using the known methods of assessment. 8. ACKNOWLEDGEMENTS

We gratefully acknowledge Arup University for funding this research and Historic England for en- gaging with us on the importance of tranquillity and the provision of tranquil spaces to people through the protection of historic assets in the urban setting. 6. REFERENCES

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