Visual significance as a factor influencing perceived risks: cost-effectiveness analysis for overhead high-voltage power-line redesign

Abstract

Residents' concerns about the impact of high-voltage power-lines often lead to conflicts in urban, suburban and rural areas, affecting the acceptance of projects and leading to additional implementation costs. This paper presents analysis which is intended to serve as a useful tool to aid decision-makers in managing these concerns, while taking the economic consequences into account. It was applied in the selection of an alternative to rerouting and/or undergrounding two 220 kV power-lines in the urban fringe. The influence of the power-lines' visual significance on perceived health and safety risks was estimated using visual factors and expert assessment. The estimated effect of visual significance was then integrated in economic analysis that linked the initial investment effort, its effectiveness and potential reinvestment costs. This analysis unblocked the process of selecting routing alternatives, informing the parties involved about the trade-offs of each option. Introducing the above-mentioned variables in the decision-making process helped make decisions more socially sensitive.

Keywords::

• power-lines
• perceived risk
• project acceptance
• cost-effectiveness

Introduction

Ordinary people are unfamiliar with the functioning and effects of technology. They consequently rely on intuitive risk judgements, called risk perceptions (Slovic 1987). Perceived risk is therefore closely related to psychological uncertainty. Risk perception can be defined as the subjective assessment of the probability of a specific type of accident happening and how concerned we are about the consequences (Sjöberg et al. 2004). Because people evaluate probability and the consequences of a negative outcome subjectively, concerns leading to opposition to technologies and demands for risk mitigation are often based more on risks that people perceive to be real, rather than on the real existence of any such risks.

Public opposition consists of rejection of a particular situation, cause or event by society as a whole or in part. Rejection may be based on belief, or on events in the past, present or future, and may have non-immediate consequences. Furby et al. (1988b) reported that, from the 1970s on, in the USA there was a sharp rise in opposition to electrical infrastructures. This was due to the densification of the electrical supply system in order to meet demand, and also to uncertainty about its effects on health and concerns about the likelihood of accidents. Additionally, the author noted that increasingly easy and immediate access to energy resulted in under-appreciation of the resulting services. The ‘invisible’ nature of electromagnetic fields (EMF) makes the nature of risk associated with high-voltage power-lines ‘unknown’, making it impossible to control (Slovic 1987). The unnatural nature of the risk has also been said to be an important factor in the acceptance of technological risk (Sjöberg 2000). Control over the risk source is a key issue that could explain different risk perceptions related to EMF. For example, the EMF strength of a hairdryer (at 30 cm) is comparable to that directly beneath a 275 kV power-line (Elliott & Wadley 2002). However, there is far less public concern about the health effects of hairdryers than there is about high-voltage power-lines. This may be due, at least in part, to the fact that users are able to simply turn off a hairdryer to make the risk disappear. All of these factors, among others, lead society to take a much more critical stance regarding the negative consequences of these infrastructures relative to their benefits.

Nowadays, some communities are exposed to a ‘danger message’ about large electrical infrastructures installed near housing areas which, regardless of its scientific basis, is strongly rooted in the collective unconscious. This message contributes to alarm that triggers public objections, which are sometimes very vocal. Conflicts between residents or organizations and authorities or electricity utilities often lead to complex situations that are difficult to solve, and this strongly influences the planning, design and implementation of energy projects (Shrader-Frechette 1988; Kunreuther et al. 1990; Metz 1992). One of the areas of decision-making in which the opportunity to accommodate social considerations and public participation is clear and relevant is Social Impact Assessment (Vanclay 2003). In Spain, as in the rest of Europe, the legislative and institutional framework promotes a comprehensive approach, and Planning and Impact Assessment processes are evolving to come to terms with these issues (Chaytor 1995; Esteves et al. 2012).

Decision-makers and professionals have become increasingly aware of the influence that social impact and psychological effects may have on project acceptability and, consequently, on total costs (Goodland 1994; Rowan 2009). However, communities often believe they are not engaged enough, or that their interests and concerns are not taken seriously in the decision-making process (Devine-Wright et al. 2010). They may also question the fairness and legitimacy of infrastructure routing processes (Shrader-Frechette 1988; Gross 2007; Devine-Wright 2007; Cotton & Devine-Wright 2011). Spanish laws regulating high-voltage power-lines (BOE 2008, RD 223/2008) only set a minimum safety distance between power-lines and houses that ranges from 4 to 6 m, depending on voltage. It is clear that these specifications do not take into consideration public unease, nor do they reflect a philosophy of seeking to avoid public opposition. As a counter-example, in 2010 the Technical Advisory and Information Service of the Spanish Federation of Municipalities and Provinces created a manual for managing of social alarm and improving risk communication at the local level, focused on mobile phone masts (FEMP 2010).

However, management of the multiple and conflicting needs and demands involved in a routing process faces the difficulty of providing a reliable service that is compatible with economic costs and avoids negative feelings. Public administrations, developers and utility managers often have to face this situation: providing a service that society demands leads to a number of negative psychological effects that lead communities to reject proposals. We refer to the paradigm of ‘risk society’, the contradiction of a society that constantly needs more material and technological development which, at the same time, it considers to threaten human well-being (Beck 1992). Once the conflict is created, perceived risk may become more difficult to manage and control than real risk, given that it is often internalized and amplified by the individual (Kasperson et al. 1988; WHO 2005). Taking into consideration the degree of concern and the attitude stakeholders adopt would prevent conflicts from arising, while enabling the optimized implementation of high-voltage power-line projects in both social and economic terms (Ciupuliga & Cuppen 2013). The framework presented by Sumper et al. (2010) allows the broad participation of stakeholders in the impact assessment of existing high-voltage power-lines in urban areas. The methodology described was based on the numerical evaluation of several impacts combined with weighting factors. Its strength did not lie in absolute objectivity, but rather in the participation of different entities and strong citizen involvement. Wlodarczyk and Tennyson (2003) presented a theoretical methodology in which changes in attitudes towards risk regarding a nuclear generation project were related to change in behaviour, as a pathway to assess social and economic impacts. Cain and Nelson (2013) developed an integrated, multilevel framework for the siting process that extended the analysis of public opposition mechanisms, including individual attitudes, social interaction and institutional context influences.

The lack of empirical evidence about how people interpret and react to high-voltage power-lines introduces a high level of uncertainty in decision-making. Personal, social–psychological and contextual factors combine to shape public understanding and acceptance of energy technologies (Slovic & Peters 2006; Truelove 2012). Project characteristics and those of the decision-making process and the location have been proven to determine public perceptions and attitudes regarding these facilities (Devine-Wright 2007). The particularities of each case are difficult to detect unless specific public consultation takes place. However, social perception assessment is sometimes difficult or impossible to conduct owing to practical or economic limitations. In the absence of conclusive social information, decisions aimed at overcoming social impact become complex, and contrasting estimations lead to a deadlock in project implementation. Neutral, objective and technically prepared mediators are then essential to strengthen the confidence of all parties involved in the decision-making process. The search for solutions thus becomes a matter of socio-economic balance while assuring that the technical solution adopted guarantees the quality and reliability of the power supply (Woldemariam & Simpson 2008). Multicriteria techniques are often necessary in order to provide the decision-maker with the necessary tools to allow her to progress in solving a problem (Vincke 1989; D'Avignon & Sauvageau 1996; Roy 1996).

This paper investigates a real experience of the management of negotiations for high-voltage power-line rerouting and/or undergrounding. The power-lines were located in a suburban area, where future residents would be likely to feel unease about electrical infrastructure in close proximity to their homes. Criteria to include this social dimension in the decision-making process were therefore required in order to prevent social rejection of the solution. This case was unique as it was not possible to conduct a public consultation (as the community did not yet exist), so the decision had to be grounded on objective-expert assessment. A model for the assessment of alternatives was thus proposed to the parties involved in the process, dealing with the effect of proximity and visual significance of the power-line in terms of perceived health and safety risk, while analysing its economic implications. The lessons learned from this process and the trade-offs of each proposed alternative are discussed.

This model does not cover all causes of perceived health and safety risk, and nor can it replace important aspects of Social Impact Assessment such as public consultations, participatory processes or psychometric studies. It is conceived as a useful tool in some phases or aspects of Social Impact Assessment: it would be operational in initial negotiating phases and would assist in assessing the visual dimension of perceived health and safety risk. Visual factors were the only relevant and available variables in this case study. In other cases, especially if a proper consultation were possible, it would have to be combined with other types of analysis.

High-voltage power-lines: perceived impacts

In the mid-1980s a series of studies, many of them promoted by utilities, began to examine public objections to electric facilities with the aim of improving the conceptual and empirical methods applied (see e.g. Market Trends, Inc. 1988; Rhodeside & Harwell Inc. 1988; Priestley & Evans 1990; Entre les Lignes 1991; Kroll & Priestley 1992). Analysis of the responses to surveys or interviews from the most important studies published to date, the International Electric Transmission Perception Project (Priestley 1996), identified perceived impacts on human health, safety, property value and aesthetics as the most important. Biophysical impacts have been also increasingly denoted as primary concerns in rural areas. Potentially negative effects on human health (stress, fatigue, headache and cancer related to EMF) and safety (electrocution, the fall of pylons, fire, etc.) are frequently considered to be the most critical issues, as several studies have found them to be the most commonly mentioned and discussed (Furby et al. 1988b; Rhodeside & Harwell Inc. 1988; Priestley & Evans 1990; Priestley & Evans 1996; Bond & Hopkins 2000; Jay 2007; Soini et al. 2011).

The perception of health and safety risk is related, sometimes very subtly, to other considerations or interests. For example, in the case studied by Cotton and Devine-Wright (2011), interviewed residents stressed their preference for higher pylons if they were very close to their homes, despite their possible visual impact, arguing that in this way EMF sources would be more distant. Furby et al. (1988a) noted that, in some cases, the focus on health effects increased as the conflict continued, perhaps because negative health effects have a significantly greater weight in regulatory and legal battles than other considerations. The effect of overhead high-voltage power-lines on the value of real estate often influences owners' attitudes, consciously or unconsciously. This impact has attracted the attention of many studies, although no conclusive results have been drawn (Furby et al. 1988a; Kroll & Priestley 1992; Elliott & Wadley 2002; Sims & Dent 2005; Chalmers & Voorvaart 2009). Kinnard and Dickey (1995) noted that ‘fear (whether reasonable or not) is (legally) admissible as an explanation of why diminution in property value has occurred’ (p. 25). These authors referred to several legal cases in which financial compensation for loss in property value was demanded, in which the mere existence of fear was accepted as evidence. Even when no evidence supports such fear, the ‘stigma effect’ may affect property value. McDonough (2003) also cited some of these cases when establishing the ‘fear in the marketplace’ theory regarding transmission power-lines as having an adverse effect on appraised valuation.

Visual significance as a factor influencing perceived health and safety risks

Physical proximity and visibility make the public more aware of the presence of high-voltage power-lines. Negative attitudes are more likely to be generated when undesirable impacts are directly experienced. This is not to say that concerns about perceived health and safety are only explained by external stimuli, as risk perception has to do with thoughts, beliefs and constructs (Sjöberg 1979). However, of the complex variables that affect such perception, visual presence and proximity are two of the factors that occur the most frequently, and this is also easy to generalize.

Boyer et al. (1978) found that the nearest residents were the most sensitive to power-line construction, and this attitude was maintained over years. The survey carried out by Economics Consultants Northwest (1987) in Montana described how only 9% of respondents who lived further than 1.6 km from a power-line thought it might affect their health, compared with 24% of those who lived closer to it. The survey conducted by Priestley and Evans (1988) showed that the majority of respondents who lived 270 m from a power-line showed varying degrees of concern about its health effects, or had some kind of concern about associated accidents. The study conducted by Market Trends, Inc. (1988) concluded that, even when informed that underground power-lines cost from 3 to 10 times more than overhead power-lines to lay, 56% of the urban population and 60% of the people living in close proximity to the power-lines or substation indicated that they would have preferred underground facilities. Devine-Wright and Batel (2013) found that burying power-lines and routing pylons away from homes and schools received the highest levels of support from consulted public compared with other mitigation measures.

When analysing the effect that seeing close-by electrical infrastructure has on residents, it is important to take into account the fact that human beings interpret visual stimuli and form an idea of what is happening around them in relation to everything in the scene. It is therefore necessary to consider the difference between visibility and visual significance. While the fact that a power-line is visible simply implies that it can be seen, the fact that it may be a significant element in the everyday visual experience of residents has more to do with visual significance (Priestley 1996). The visibility of power-lines can be easily and accurately calculated using Geographical Information Systems. In the study of power-lines' visual significance, other factors that determine visual context should be included, to offer a more realistic estimate of how humans perceive them. Some of these factors are related to the characteristics of the elements observed (power-line design factors), distance from the observer, the prominence of the elements in the territory and elements that form the context in which these facilities are positioned (Higuchi 1988; Priestley 1996).

A model based on proximity and visual significance to inform negotiation in a conflict of interests

General description of the negotiation in a conflict of interests

The case study affected an area where several high-voltage power-lines ran in different directions from an electric substation that was an important power supply source for the city of Madrid. When the urban fringe of the nearby town approached these pre-existing infrastructures, it was decided to develop the free areas surrounding them. A conflict then arose between the utility and the developer, and this also involved the municipality and the regional government. This conflict arose owing to the likely objections of future residents to the presence of high-voltage power-lines close to their homes, which the utility demanded be minimized.

Consequently, the utility and the developer, assisted by the regional government, undertook an analysis of six alternatives for rerouting and/or undergrounding two 220 kV power-lines, while maintaining the substation facilities and the route of the 400 kV power-line. This case study was unique as it was not possible to consult residents, given that the community did not yet exist. The parties involved did not agree on how the alternatives would impact the community, and when the negotiations stalled it was decided to resort to external assistance to conduct the assessment. A model to assess the alternatives was then designed, to create a framework in which the conflicting parties could agree on arguments as legitimate means of reaching an agreement. The steps followed to manage the process and the model itself are presented in Figure 1.

Figure 1 Framework for the assessment of alternatives.

Description of alternatives

The electrical infrastructure consisted of a substation from which two corridors started, one running to the West and the other to the South. One 400 kV and two 220 kV overhead power-lines crossed the area through the corridors. Another 220 kV power-line was already underground and ran from the substation to the Southeast. Only the 220 kV power-lines were subject to change, since modification of the overhead 400 kV power-line was too costly to be considered a viable option. Relocation of the substation was considered over the mid to long-term, although there was no planned schedule for this. This process will presumably take time, and the substation had to be considered as permanent in the area for at least several decades.

The area was located in close proximity to the West of the town. The planned residential area surrounding the electrical substation and corridors was confined to three housing development areas. These were already plotted but no houses had yet been built (a total of 45 ha, with planned construction of over 750 houses). It was a nearly flat area, except for a 10 m high hill. The zone was devoid of woody vegetation so that the power-lines could be seen with the naked eye. The surrounding areas were predominantly farmland.

The six different options proposed were distinguished mainly by the overhead or underground length of the two 220 kV power-lines, the distance from the development area and the number and specific locations of pylons. A sketch depicting the approximate layout of elements is shown in Figure 2. A summary of the characteristics of the proposed alternative, as provided by the utility and approved by all the parties involved, is shown in Table 1.

Figure 2 Sketch showing the alternative power line rerouting and/or undergrounding (the dotted line corresponds to underground power lines), development areas, substation and terrain elevation.

Table 1 Summary of the power-line design characteristics for each alternative

Design characteristics and costs of the alternatives of two 220 kV power-lines rerouting and/or underground
Alternative		Aerial total length	Underground total length	Pylons (sum of two power-lines)	Implementation costs (million Euros)
Alternative 1	Two overhead power-lines in the west corridor	2500 m	0	4+5	3
Alternative 2	Two overhead power-lines in the south corridor, linking the west corridor	3250 m	0	7+5	4
Alternative 3	Two partially underground power-lines in the W corridor, going overhead in the proximity of the substation and 100 m from the house fronts	1200 m	1300 m	3+3	8
Alternative 4	Two underground power-lines in the west corridor, going overhead 100 m from the house fronts	650	1850 m	2	12
Alternative 5	Two underground power-lines in the west corridor, going overhead 500 m from the house fronts	0	2500 m	2	16
Alternative 6	Two underground power-lines in the south corridor, going overhead 100 m from the house fronts	700	2000 m	2	15

Description of the parties and interests involved

Prior identification of the parties involved and their relationships was necessary, in order to form a clear idea of the conflict of interests. In the case study, the developer and the utility were the directly conflicting parties, while the municipality and regional government were indirectly involved. The future residents and the general public were identified as indirectly involved, since their interests had to be considered in the decision adopted even though they could not be consulted.

Several meetings with the developer and the utility then took place, in order to clarify their points of view. Both parties therefore had an opportunity to express their aspirations and constraints. On the one hand, the promoter was responsible for power-line redesign costs, as the electrical infrastructure was in place before the building plan was approved. Unblocking the situation allowed them to build the houses and recoup their initial investment. However, they could not accept very high implementation costs. On the other hand, the utility would manage the electrical infrastructure once the rerouting project was implemented and the community established. As the managing body, the utility did not want to take on a high risk of social opposition that would probably demand a redesign, as they would have to manage the situation and pay for the extra costs. The regional administration risked becoming involved in a long legal battle in which it may finally be said to have a pecuniary responsibility. The municipality was underfunded and saw the development plan as a source of income. Future residents would move to the area only after the rerouting alternative had been implemented, and would be directly affected by the decision made. Finally, it was important to consider that extra costs may eventually be borne by general power consumers, through an increase in electricity charges.

The assessment of the alternatives was consequently conducted by taking into account all the interests involved, while trying to balance the trade-offs accepted by all parties. Once the analysis was completed, a final meeting was held in order to present the results and collect impressions.

Identification of influential variables

Four general types of variables were analysed in terms of their influence on the decision-making process: biophysical impacts, technical requirements, social impacts and economic constraints.

Biophysical impacts were not considered to be significant in the case study, since the power-lines were confined to a suburban area surrounded by farmland and wasteland, crossed by recently constructed roads and with housing development areas ready for building work. No outstanding value was threatened and no fauna seemed likely to be very much affected by the change.

Technical requirements involved the reliability and quality of the power supply. The technical department of the utility expressed no concerns or preferences in this respect when consulted. The quality of supply was assured in all of the alternatives. Only the higher cost of operating and maintaining underground power-lines was mentioned, while acknowledging that savings owing to their higher reliability often compensate for these extra costs.

Of the social impacts, perceived health and safety effects were identified as critical, as opposed to visual impacts or effects on property values. The substation and the 400 kV overhead power-line, which will not be altered, had the greatest visual impact. New residents will take the pre-existence of electrical infrastructure into account when they decide what to pay for a house. Probable public objections related to perceived health and safety risk were then said by all parties to be decisive for project acceptance, grounded on previous experience and given the proximity of the development areas to power-lines. The actual health and safety risks were said to be low. The potential effects of EMF exposure on human health depend on their frequency and strength. It has been proven that the strength of an EMF falls sharply with increasing distance from the source (WHO 2005). For a 400 kV overhead or underground power-line, EMF strength is not significant beyond around 60 m (Andreu et al. 2003). As no houses will be located less than 80 m from the power-lines, there were no real health risks caused by EMF exposure in the case study. Safety risks are only critical when overhead components are in place and in close proximity to public gatherings. In the case study this was associated with pylons (falling or accidental contact) and where power-lines cross roads. However, this risk was considered to be low and additional measures could be taken to increase public protection (structural reinforcement, perimeter fences or walls, elements to deter climbing, etc.). Lines breaking or fires were considered non-significant risks, given the climatic conditions and the dominant land cover.

Economic constraints were a critical aspect in considerations, as the conflicting parties were liable for a range of high costs which varied significantly among the alternatives, depending on the overhead/underground power-line ratio.

It was therefore necessary to select the factors that made it possible to identify the alternative that mitigated the perceived health and safety risk, making the investment cost-effective. In the absence of empirical evidence (the community could not be engaged), it was necessary to draw on factors that were as objective as possible, as well as to assess their influence by an expert weighting process. Factors relating to the visual significance of the power-line were then proposed, acknowledging that perceived risk could only be partially predicted. These were the only available factors in connection with perceived health and safety risks, and the conflicting parties agreed on their importance. This was based on the assumption that the closer and more visually outstanding a power-line is, the stronger the awareness of its presence and, consequently, the greater the sense of a threat to health and safety.

Development of the model to assess the alternatives

Once the interests involved and the factors influencing the decision-making process had been clarified, a model was developed to compare the trade-offs of the alternatives. This was structured in two interrelated phases. In Phase A the likely effect of visual significance as a daily reminder of a possible health risk was assessed. The results of this were then included in Phase B, which aimed to analyse the cost-effectiveness of each alternative.

Phase A: visual significance assessment

Characterization of factors

The visual significance of power-lines was characterized by three interrelated visual/proximity factors: factors in connection with power-line design; critical areas where viewers concentrate; and zones of visual significance.

The first step was the selection of power-line design factors that affect observers. These were related to the number and combination of the different components of power-lines (Table 2).

Table 2 Power-line design factors

Power-line design factors	General criteria
Number of pylons visible	Residents become more aware of the presence of the power-line as it is directly visible and relatively close.
Length of power-line visible	Residents become more aware of the presence of the power-line as it is directly visible and relatively close.
Pylon density effect	Areas where the number of pylons is dense, especially where they are very clearly visible (e.g. on a hill), making them more noticeable.
Distance to nearest pylon/power-line	The nearest elements potentially have a significantly higher impact on the viewer.
Overhead road crossing	Residents are more aware of the presence of a power-line owing to its direct visibility, its proximity and perceived noise.

The second step was to determine the visual significance of power-line design factors. The Viewer Critical Concentration Areas (VCCA) were then identified as the vantage points from where the greatest number of potential observers would directly and frequently see the power-lines. The outer perimeter of each developable area and the roads were deemed VCCA in the case study. These locations were considered to hold the greatest number of potential observers, and they certainly had a direct view of the facility.1 Roads were also considered critical areas since some sections were very close to pylons, and overhead power-lines passed over them at several points. The VCCA served to determine the Zones of Visual Significance (ZVS). A map of zones of visual significance was therefore drawn up, according to distance from VCCA and visual context. The VCCA and a sketch of the ZVS are depicted in Figure 3, based on the criteria listed in Table 3.

Table 3 Delimitation criteria for zones of visual significance

Distance zones	Distance from VCCA	Comments
Zone 1 (no power-lines in the band)	0–50 m	While some authors have stated that the significant effect of high-voltage power-lines on the observer occurs up to a distance of 800 m, some believe that this extends out to where they are visible (Kinnard & Dickey 1995). In the case study, it was considered that there were no significant differences in the effect at 500 m and over.
Zone 2	50–100 m
Zone 3	100–250 m
Zone 4	250–500 m
Zones of special visual context	Visual context within the distance zones
SE zone	100 m around the substation	The substation and the 400 kV power-line both greatly influenced the scenic background of the two 220 kV power-lines. Also the elevation of the terrain (a hill between two development areas) heightened the prominence of the power-lines and consequently their visual significance.
Hill zone	Elevated area

Actual safety risks were considered to be so low that they did not need to be taken into account in the analysis. Nevertheless, they were implicitly included in the assessment, as they depended on factors already included in the visual significance analysis: overhead road crossings, number of pylons or proximity to areas were people gather. Owing to the visual characteristics of the area (which is highly visible), the actual risk and visual significance effects followed the same pattern of variation for all of the alternatives.

Figure 3 Viewer critical concentration areas and zones of visual significance defined in the case study.

Factor weighting

The relative contribution of each factor to the overall effect was weighted by a panel of six experts. All of the experts were selected from a scientific-academic background and had experience in spatial planning and environmental impact assessment. Their independence was assured as none of them were connected with the interested parties (promoters, managing body, regional administration or municipality) and they were not informed about who the conflicting parties were, nor about the interests involved.

In order to assist the experts in their weighting process, an objective and clear description of the power-line characteristics, layout and location relative to VCCA was provided. The information was supported by maps, photos and simulations (Figure 4). The experts had to resolve the relative importance of the electrical elements, distance and visual context using a linear weighting scale from 0 to 10, applied to ZVS and power-line design factors. The results of the weighting process are summarized in Table 4.

Figure 4 Example of the images shown to the experts during the evaluation process.

Table 4 Mean weightings assigned by experts to power-line design factors and zones of visual significance

Zones of visual significance	Mean weighting (Wz)
Zone 1 (0–50 m) (no power-lines in the band)	0.0
Zone 2 (50–100)	0.28
Zone 3 (100–250)	0.18
Zone 4 (250–500)	0.11
Substation zone	0.18
Hill zone	0.25
Power-line design factors	Mean weight (Wp)
Pylon density effect	0.25
Distance to nearest pylon/power-line	0.22
Number of pylons visible	0.21
Overhead road crossing	0.19
Length of power-line visible	0.13

As expected, the experts assigned a significantly greater weighting to the presence of power-lines in the closest band to viewers, at a level equivalent to that assigned to the visual significance highlighted by an elevated position on the hill located between the houses. However, the presence of the substation in the scene was considered to have a variable effect. Some evaluations highlighted the negative effect of adding a new structure to a scene where a similar infrastructure already exists. Others tended to consider that the presence of the power-line was somewhat ‘diluted’ in a scene saturated with facilities.

Regarding the contribution of each power-line design factor, the presence of pylons was considered to have a significantly higher negative effect compared with that of power-lines. This result is consistent with the findings of Chalmers and Voorvaart (2009), who noted that viewers rarely perceived power-lines clearly unless their supporting structure was visible. Concerning the arrangement of pylons, their densification was found to be of greater relative importance than distance from the nearest element or the number that were visible. With regard to overhead power-lines crossing roads, experts assigned a higher weighting to this factor than they did to length of power-line visible, stressing the importance of the proximity effect and perceived noise at these points.

Index calculation

The visual significance of power-lines for each alternative was calculated as the weighted sum of partial indices, which estimated the effect of each power-line design factor, taking into account its location in each ZVS:

where I_factor is the effect raised by each power-line design factor considered and W_factor are the weightings assigned by experts to each factor.

In some cases the estimate made by the partial index was based solely on quantitative data, such as the visibility of pylons/power-lines from VCCA. For other indices, the use of systematic calculations was either impossible or insufficiently descriptive. In these cases the experts had to make a qualitative assessment by weighting each alternative, assisted by an objective description of data and each visual situation. Table 5 shows the estimated visual significance of the power-lines, as well as the relative contribution of each factor to the overall effect as assessed by the group of experts. As this estimation is a comparative analysis of options, the results simply show a relative effect that lacks significance unless it is related to the other alternatives.

Table 5 Assessment of likely power-lines visual significance for each alternative considered. Partial factors and index calculation are presented (ZVS = Zones of Visual Significance; VCCA = Viewer Critical Concentration Area).

Factor	Partial index calculation (Ifactor)	Factor Weighting (Wfactor)	Weighted Results
Alternative 1	Alternative 2	Alternative 3	Alternative 4	Alternative 5	Alternative 6
Number of pylons visible	, normalized on a linear 0–10 scale; Nz, number of pylons visible in each ZVS/Wz, weight assigned to each ZVS (see Table 4)	0.21	2.10	1.68	1.26	0.53	0.21	0.63
Length of power-line visible	, normalized on a linear 0–10 scale; Lz, length of power-line visible in each ZVS/Wz, weight assigned to each ZVS (see Table 4)	0.13	1.30	0.85	0.33	0.13	0.00	0.20
Pylon density effect	; We, weight (linear 0–10 scale) assigned by each expert to each alternative, considering the number of pylons accumulated, position and direct/indirect vision of the pylon	0.25	2.20	1.95	1.40	0.10	0.10	0.10
	Alternative 1: a group of five pylons located between two fronts of development areas, directly viewed (150 m away)
	Alternative 2: a group of six pylons on the hill, partially viewed
	Alternative 3: a group of four pylons in front of the electrical substation, directly viewed
	Alternatives 4–6: minor accumulation (no more than two pylons)
Distance to nearest pylon/power-line	; We, weight (linear 0–10 scale) assigned by each expert to each Alternative considering distance, VCCA length and direct/indirect vision of the pylon/power-line	0.22	2.16	1.72	1.58	1.14	0.26	0.35
Overhead road crossing	; We, weight (linear 0–10 scale) assigned by each expert to each Alternative considering	0.19	1.56	1.67	0.00	0.00	0.00	0.00
	Alternative 1: four overhead road crossings
	Alternative 2: two overhead crossings and a power-line running 150 m parallel to the road
	Alternatives 3–6: no overhead road crossings
	Estimated Visual Significance Index		9.32	7.87	4.57	1.90	0.57	1.28

Phase B: cost-effectiveness analysis

The effect of the visual significance of power-lines was included in cost-effectiveness analysis, in order to show its full practical significance. The interests of all parties involved in the negotiating process, as well as future residents and electricity users' concerns, could thus be analysed.

Characterization of factors

The economic analysis was divided into three components, to clarify the current and future economic implications for both of the parties which are directly involved (the promoter and the utility), as well as for future residents and electricity users:

• Initial investment effort – the initial cost of implementing each alternative takes into account the relative economic effort in power line redesign undertaken by the developer. As the result of negotiations, the initial investment did not correspond to the utility, as the electrical infrastructure was already in place when it was decided to develop the area. Consequently, these costs will never be borne by electricity users. On the other hand, this may affect property values: future residents will eventually pay a higher price for their houses as a consequence of benefiting from a higher-quality residential environment.

• Initial investment effectiveness – the usefulness of the initial investment was evaluated by considering the degree to which it reduced the visual significance of power lines. The maximization of this variable is, after all, a profitable result for both the promoter and the utility. Future residents would also be beneficiaries, as this factor takes into account cost optimization while improving their living environment.

• The cost of risk taking – this component takes into account the economic effort of the holder of the infrastructure after it has been installed (the utility), in terms of reinvestment costs in the case of power line redesign to reduce visual significance in the future. As a variable which covers future extra costs that could eventually be transferred to users, its minimization responds to the interests of general customers since it prevents an increase in electricity bills.

Regarding the cumulative cost that the utility and general electricity consumers may have to pay over the long term, the costs of regular actions involved in operation and maintenance were analysed to assess their relevance. These would vary depending on the ratio of overhead/underground power-line in the alternatives. Based on the data provided by (Andreu et al. 2003), the approximate costs of overhead and underground power-lines would be 1100 and 1700 Euros/km per year, respectively (excluding regular tree pruning). This amounts to at least 65% of additional cost for underground power-lines. Nevertheless, as the maximum difference of underground length between alternatives was 2500 m, the maximum difference in operating/maintenance costs would be 4250 Euros per year. In any case this would result in a substantial additional cost for the managing body (and eventually for customers). Even over the long term, these costs would be minor compared with the investment required to redesign the power-lines, so they were not included in the analysis. Operation and maintenance costs only would represent a significant economical factor for larger power-lines.

Factor weighting

The experts had to weight the relative effect of each economic factor on a linear scale from 0 to 10. The mean weightings assigned are shown in Table 6.

Table 6 Results of the cost-effectiveness analysis showing economic factors and index calculation

Input Parameters		Alternative 1	Alternative 2	Alternative 3	Alternative 4	Alternative 5	Alternative 6
CostAlt_i: Initial investment required to implement each alternative, millions of Euros (see Table 1)		3	4	8	12	16	15
Visual Significance Index: IVisualAlt_i (see Table 5)		0.93	0.79	0.46	0.19	0.06	0.13
	Factor Weighting	Factor Calculation
Economic Factors (Ifactor)	(Wfactor)	Weighted Factor (Ifactor·Wfactor)
Initial Investment Effort
Cost of each alternative relative to the most expensive alternative, normalized to a linear 0-10 scale		1.9	2.5	5.0	7.5	10.0	9.4
maximum effort (most expensive alternative 10 ––––––––––– 0 no cost, no effort	Wini = 0.4	0.8	1.0	2.0	3.0	4.0	3.8
Initial Investment Effectiveness
Relative efficacy of investment in reducing visual significance, normalized to a linear 0–10 scale
		Eff = 2.3	5.3	6.8	6.8	5.9	5.8
		10.0	3.4	0.0	0.0	2.0	2.2
minimum effectiveness 10 –––––––––––––––––– 0 maximum effectiveness	Wief  = 0.2	2.0	0.7	0.0	0.0	0.4	0.4
Cost of Risk-Taking
Combination of the likelihood of redesigning each alternative and costs of reinvestment,^* relative to the highest value among the proposed alternatives, normalized to a linear 0–10 scale		redesign to Alternative 5 = 16 million Euro extra cost	redesign to Alternative 6 = 15 million Euro extra cost	redesign to Alternative 5 = 8 million Euro extra cost	redesign to Alternative 5 = 4 million Euro extra cost	–	–
		CRT = 14.9	11.9	3.7	0.8	0.0	0.0
maximum cost of risk taking 10 –––––––––––––––––– 0 no cost, no effort		10.0	8.0	2.5	0.5	0.0	0.0
	Wcrt = 0.4	4.0	3.2	1.0	0.2	0.0	0.0
Cost Effectiveness Index
		6.8	4.9	3.0	3.2	4.4	4.2

^*The reinvestment cost corresponds to the extra cost of power-line undergrounding in order to adapt it to the alternative with lowest triggering effect, being Alternative 5 or 6 depending on the layout.

Index calculations

The cost-effectiveness of the alternatives was calculated as the weighted mean of each economic factor:

where I_ini is the index of initial investment effort, I_ief represents the relative effectiveness of the initial investment, I_crt is the index of cost of risk-taking and W_xxx represents the weight assigned by experts to each economic factor. The contribution of visual significance to generating public awareness of the presence of power-lines corresponds to calculating the second and third economic factors. The selection of the alternative was based on the lowest result in I_economic. The contribution of each economic factor to the final outcome is shown in Table 6.

Analysis of results

The results show Alternative 3 to be the one that best balanced the economic interests of all parties while sufficiently reducing the effect of visual significance on viewers. Indeed, it contained the initial cost and brought it closer to the effort involved in accepting the reinvestment risk. In addition, the initial investment effort was the most effective, that is, it was the alternative in which visual significance of the power-lines decreased the most for every million Euros invested. Alternative 3 was therefore shown to be the most favourable. The graph in Figure 5 clearly shows this balance, as well as highlighting the factors that decisively penalized the other alternatives.

Figure 5 Graph of each factor's contribution to the assessment of the alternatives considered.

Thus although Alternative 4 seems to be a solution that is similar to Alternative 3, it was penalized by high initial investment costs. Alternatives 5 and 6 were also strongly penalized by the initial investment costs of undergrounding the power-lines. The above-mentioned costs would hardly be found acceptable by the promoter. However, the risk of extra costs incurred by a possible redesign of power-lines would be minimal. Conversely, Alternatives 1 and 2 showed relatively low implementation costs, although they involved running a high risk of power-line redesign owing to public concerns deriving from their visual presence. This risk could lead to a very high extra cost of reinvestment. Additionally, the initial investment would be very inefficient, since both alternatives hardly reduced the visual significance of the power-line.

The detailed procedure and the results were presented to the parties involved, which had the opportunity to express their objections. Finally, Alternative 3 was recognized as the one which best balanced trade-offs, and the methodology successfully served to unblock the negotiating process.

Conclusions and lessons learned

The methodology presented was conceived as an instrument to allow all parties to deal with social concerns, relating them to their economic consequences. The framework proposed allowed them to clarify the implications that negative feelings arising owing to the presence of power-lines may have. In the case study, this impact could not be gauged by means of a proper public consultation or participatory process. Estimation of the same therefore had to take place by considering only those variables that clearly influence public concerns and are measurable, acknowledging that only some aspects and not the overall effect were being addressed. In this particular case, only proximity and visual significance were identified as available factors in connection with perceived health and safety risks. The model was therefore intended to assess only the indirect effect of the visual dimension in creating concern. In other cases it would be possible to conduct a proper Social Impact Assessment, including a community consultation and a broader set of factors deriving from influential variables and constraints analysis.

As noted by Elliot and Wadley (2002), there is a lack of information about the conflicting situations in connection with high-voltage power-lines and how they are resolved. The experience described could be helpful in this regard, and the lessons learnt could inform future actions. To date, information on the subjective considerations of residents regarding the impact of electric facilities on their safety and health is neither proven nor sufficiently consistent. The variables affecting public attitudes are diverse, and there are complex relationships between them. A further improvement of the study would be to collect future resident impressions in order to monitor the actual effects of the selected alternatives. This post-construction evaluation would make it possible to design a more accurate image of social concerns and to compare the opinions of experts, utilities and government against public perceptions, thoughts and beliefs. It would clarify several uncertainties arising in situations of this type.

An important value arising from this experience is the recognition that strategic planning considering the full range of social impacts (including perceived impacts) and engaging all stakeholders would prevent conflicting situations that are detrimental for everyone. At very early phases of the decision-making process, analysing community impact prior to actually engaging with a community may be a very useful starting point. The methodology proposed could pre-evaluate some of the implications related to perceived impacts, in addition to real ones, undertaking an initial analysis of influential variables to guide further discussions with communities. The study case dealt with high-voltage power-lines near housing developments, one of the facilities that most often gives rise to public concerns. Moreover, by introducing certain adjustments in its predictive parameters and procedure, this model could be adapted to other types of facilities, such as mobile phone masts, landfills and wind farms.

It is clear that undergrounding high-voltage electrical facilities greatly increases costs in comparison with the maintenance of overhead power-lines. Nevertheless, it is also far more effective in reducing likely concerns, and it also leads to a number of other benefits. For example, the study carried out by Johnson (2006) for the Edison Electric Institute showed that underground power-lines cost significantly more than overhead ones, and that their advantages in terms of reliability are unclear. However, this study acknowledged the existence of substantial benefits which are harder to quantify (the study focused on visual improvement), which means that many communities prefer underground power-lines. Undergrounding power-lines significantly increases the likelihood that a project will be socially accepted and, as has been shown, this will prevent further cost overruns. This can additionally allow a greater use of the housing area and a higher-quality environment for life. It would therefore result in greater benefits for the municipality and the promoter, while contributing to the well-being of residents. It is also necessary to consider that public opposition to power-lines in a particular area could have a rebound effect and trigger negative attitudes towards other nearby power-lines.

In the case study, there would be additional measures to reduce the impact of power infrastructure once it had been constructed. The type and arrangement of houses in each of the plots could not be considered in the study, but these would be complementary factors that would modify the visual salience of power-lines. Likewise, landscaping public land and using it to provide compensating amenities can positively affect the perception of residents regarding the risks of these infrastructures (Priestley & Evans 1996).

Acknowledgements

The authors would like to thank the Industry, Energy and Mines General Office of Madrid for the support of this project. The authors also thank the two anonymous reviewers for their useful comments.

Notes

^1. While the layout of houses significantly determines the proximity and the visibility of power-lines, this could not be considered in the study. At the time, the arrangement of the blocks of buildings was not defined, since the developable areas still lacked the construction project.