The proportion of the world's population living in large towns or cities has grown from around 5% to 50% over the past two centuries. Demographers estimate that by 2030 approximately two-thirds of all people will live in large towns or cities. The human population is thus becoming urbanized (Anthony, 2000). Through the recent process of urban development, characterized by urban expansion and redevelopment, industrialized countries have witnessed a surge in the number, scale and complexity of urban structures. However, it has become difficult to ensure that urban space meet the demands of society. These demands include upgrading social infrastructure in a sustainable manner and the regeneration of attractive urban space that is not only safe and highly efficient, but also conscious of psychological impact.

In contemporary urban spaces, large-scale high-rise buildings are profuse. The massive construction of high-rise buildings is continuing so that there are more than 500 buildings in Japan whose height exceeds 100 meters (Munakata, 1998; Otobe, 2006). High-rise building clusters increase the usability of urban space but on the other hand they make oppressive cityscapes, which are visually sensed by residents and visitors. These cityscapes bring feelings such as discomfort, oppression and invasion of privacy (Hwang, 2007). The term "oppressiveness" is coined as a translation of the Japanese word "圧迫感" (appakukan). This word refers to cityscapes that feature high-rise buildings which cause negative psychological pressure on residents. In previous research in Japan, "圧迫感" has been referred to with these words: "Oppression", "Sense of Oppression", "Oppression Feeling" and "Sense of Physical Oppression". The word "Oppressiveness" is said to contain the hidden meaning of physical magnitude. Oppressiveness is a barrier to achieving sustainable urban development.

Neuman (2005) reviewed empirical evidence as to whether compact cities represent a form of sustainability while others have shown a negative relation. These inconsistent relationships may be partly due to methodological problems. Different studies have used different indicators for compactness and sustainability, and many studies have suffered from a lack of control over potential confounding factors. However, aside from these methodological issues, it seems apparent that compact buildings have not always fulfilled its promise of attaining a shift in community development toward more complete sustainability. Explanations of the un-sustainability of compact cities have focused mostly on the ineffectiveness of urban management (Jenks & Burgess, 2000; Williams, Burton, & Jenks, 2000). In particular, there is increasing recognition that psychological factors play a role as well. It has been argued that there is an inherent tension or paradox between the notion of the compact city and people's desire for a spacious, green, and quiet environment (cf. Wiersinga, 1997).

academics (Hwang, 2007; Byun, 2009; Takei 1979; Hirate, 1995). Through a research project aimed towards measuring the oppressiveness of buildings, Takei et al (Takei, 1977.9, 1977.11, 1978.9) concluded that the parameters of the physical shape of buildings is the driving factor of oppressiveness. Takei suggested that the solid angle and configuration rate of buildings are the best indicators for oppressiveness. The research determined that the permissible value of oppression is up to 8% building's configuration factor. In the case of a building with a configuration factor of over 4%, the building should be discussed as an influential element in the urban environment (Takei, 1978.1).

Hwang (2007) added the distance of viewer to the building (r) and developed the formulation to where O is the "Oppressiveness Perception".

buildings as producing an alleviating affect on oppressiveness. (Takei, 1981) Takei et al (1983) in his research showed "tree-planting in the area around single-standing building has an impact on reducing the feeling of oppressiveness". To-date, the mitigating effect of trees on oppressiveness of cityscapes remains "unmeasured".

This research was conducted to clarify the effect of trees in "real" urban environments, to examine the different distances from trees and buildings and different kind/percent of urban greenery in the field of view. Also to assess the influence of trees in narrow sidewalks on oppressiveness (圧迫感:appakukan) and on the feeling of freedom experienced in open spaces or 'openness' (開放感:kaihoukan) as well as to assess the relation between the effect of trees' and sky in terms of oppressiveness of cityscapes. The end goal of this research is to facilitate decision making of urban policy makers by creating a formula that included the influence of urban trees'. This research also looked at the accuracy and applicability of findings in different countries. The research findings from the cross-cultural comparison on oppressiveness show that further research is needed in this area.

The first experiment was conducted in the real urban environment of Hongo area in the center of Tokyo. Hongo Street was chosen for this experiment due to its characteristics that resembles a typical Japanese street with narrow sidewalks and high-rise buildings. This experiment was done to clarify the effect of trees on oppressiveness and assess the compatibility of Takei et al.'s (1983) research on Greenery's effect on oppressiveness in the "real urban area". Five building compounds were selected, all located in the Hongo area and twenty people were asked to sit on small chairs in front of the buildings and fill-in the pre-designed questionnaire. The mathematical value of "Solid Angle" was evaluated for all urban elements of each of the 15 cityscapes. This included trees, buildings and sky. Results showed that trees significantly reduced the oppressiveness of cityscapes. The results of the experiment were in accordance with Takei et al research but they showed more complexity relating to the effect of trees on human psychology. The perception of oppressiveness and openness are inter-connected. When an urban element successfully reduces oppressiveness (e.g. trees), it simultaneously reduces the perception of openness. The secondary effect of reducing openness is undesirable for the urban environment. Through the research it could be understood that in the urban area, many factors are influencing people and investigating the effect of only one or a few elements on human psychology is complicated. The similar effect of trees and sky on human psychology in terms of oppressiveness and perception of openness as well as the complicated effect of trees, observed in urban area led this research to do the second experiment in a more controlled environment.

The second experiment was conducted to assess the relation between the effect of trees and sky in terms of the perception of oppressiveness in urban environment. The fact, observed by many researchers including first experiment of current research showed that sky and trees have a similar mitigating effect on oppressiveness. In terms of environmental psychology trees could be addressed as pieces of sky on the streets. The second experiment was conducted to clarify this relation in a controlled experimental room. The other aim of this experiment was to separate trees, sky and buildings from other urban elements and study their effects on each other in a controlled environment. One of the cityscapes of Hongo Street was chosen and reconstructed utilizing 3D-Computer Graphics. Different "numbers" of trees in different "distances" from the observer as well as different "building heights" were adding, in total 48 photos were generated for the assumed to have a similar effect with trees, and thereby mitigate the oppressiveness, but results showed the opposite. The impact of greenery on the facade of the building is either not significantly positive or totally negative. The location of greenery on the facade of the building showed significant impact on the perception of oppressiveness. The higher the greenery is on the building's facade, the better the impact is on oppressiveness. This shows that not all types of greenery would contribute to the urban environmental psychology in the same positive way. It is possible that the impact of greenery on the facade could be improved if a more aesthetically pleasing design was applied to the greenery on the facade.

The results of this experiment challenge the part of the idea of green urbanism, which focuses on increasing the quantity of greenery in the urban area in order to achieve a better urban environment. In fact, this research shows that further research on the assumptions of green urbanism theory is necessary. This research aims to provide a tool to assist policy decision makers improve the urban environment and therefore needs to be applicable in different cities and countries. The next experiment looks at whether oppressiveness could be different from nation to nation. This question led current research to the next and final experiment of this thesis.

The fourth experiment was conducted to assess the influence of nationality and cultural background on the perception of oppressiveness.

So far, the research about oppressiveness and openness in the urban environment has been conducted only in Japan. That is also why the word "圧迫感" (apakukan) and "開放感" (kaihoukan), which are equivalent to "oppressiveness" and "openness" respectively, are Japanese concepts. Other nationalities might also feel this oppressiveness even if they don't have specific words or research. Therefore proving the applicability of these concepts to other nations would prove the transnational nature of the problem. Twelve photos from the "Marunouchi" area in central Tokyo and twelve photos of the area around "Victoria Street" of London were selected and shown to twenty Japanese and twenty British nationals in Tokyo and London respectively. Results showed that while there are differences in perception of oppressiveness, British perceive a significant amount of oppressiveness, however, the oppressiveness perceived by British nationals is significantly less than Japanese nationals. Through the analysis, a significant difference between females and males was also observed. Women showed more sensitivity to oppressiveness than men and their responses changed dramatically when greenery was introduced to the scene.

Results showed that the difference between the Japanese males and females was less than the difference between British males and females. These results show the importance of introducing and defining oppressiveness in other countries and addressing the problem in order to make the urban environment more livable.

In conclusion, this research is a step towards identifying the key parameters of healthy urban landscape. This in turn will help researchers and urban policy makers to understand which kind of landscapes have the strongest positive psychological effects, and therefore, from a health and well-being perspective, what can be done to improve urban settings in terms of research and regulations. Further development of the formulation can give concrete decision-making power to policy makers in terms of legislating regulations for the construction of cityscapes that are less oppressive. Such an understanding would then contribute to the search for functional urban architecture beneficial to human health and environmental sustainability.

本論文は,最近の急速な都市化において,社会的インフラストラクチャーと都市建築は,安全で効率的であるだけでなく,持続可能な方法に展開することで,魅力的な都市再生を目指すべきであるとの基本的な認識のもと,都市空間の圧迫感は持続可能な都市の発展への障害になるという観点から,都市空間における圧迫感への緑の視覚的効果を明確化にするための一連の実験をまとめたもので,この緑の効果を明確にすることで都市政策立案者の意思決定を容易にすることができるとしている。

本論文は,6章から構成されている。

第1章は,研究の背景などの導入部分で,都市の持続可能性,安全性,美しさという基本的な問題意識から,都市景観における圧迫感を取り上げて論じ,さらに既往研究の整理をすることで,本論文の位置づけを行っている。

第2章は,第1の実験,すなわち東京の都心部の街路で行った20名の被験者による現場評価実験について述べている。実験によって得られた圧迫感や開放感と樹木,建物,天空の立体角などの物理指標との相関関係を分析している。その結果として,樹木が圧迫感の緩和効果を示すこと。空も同様な効果があること。圧迫感については,視点からの建物への距離が非常に重要な要因であること。開放感と圧迫感な知覚が互いに関係していること。樹木などの都市の要素が圧迫感を減らすと同時に開放感を減らすこともあること。などを導き,効果的に圧迫感を減少させて,開放性を増大させるために都市環境を管理することで,持続可能な都市建築を生み出すとしている。

第3章は,第2の実験,すなわち都市環境における圧迫感の知覚に関して,樹木,建物,天空などの効果をより系統的に検討するために,コンピュータ・グラフィックスにより建物高さ,樹木までの距離,樹木密度を変化させた48実験対象を用いた,40名の被験者による統制実験について述べている。その結果として,樹木が天空と同じように圧迫感の緩和に効果があり,その緩和効果は建物が高いほど大きいこと。樹木の効果は天空の効果より小さく複雑であること。樹木の効果は視距離によって影響されないこと。建物の前面を覆う樹木は圧迫感を減少させる効果があること。開放感への樹木の効果は建築物の高さによって影響を受けること。天空を覆う樹木は,開放感を減らすことに関係する。などを導き,圧迫感と開放感の知覚に関する定式化を行い,開放感を減少させないように天空を避け建物の前面だけを覆う緑が,圧迫感を減少させる選択肢としては望ましいとしている。

第4章は,第3の実験,すなわち建物の壁面緑化の圧迫感に対する効果を測定し,第3章において得られた建物の前面の樹木の効果と比較するために,コンピュータ・グラフィックスにより建物壁面における緑化割合,割付法,葉密度,および建物高さを変化させた51実験対象を用いた,20名被験者による実験室実験について述べている。その結果として,建物の壁面緑化が樹木とは異なり圧迫感の緩和効果が見られなかったことを導いている。また都市の緑の効果を考える上で,植物の種類やデザインの検討が重要であるとしている。

第5章は,第4の実験,日本独特の概念されている圧迫感に関して,文化的背景の影響を評価するために,東京とロンドン都心部の街路写真24枚を対象として,日本と英国でそれぞれ20名の被験者で実施した,画像評価実験について述べている。その結果として,本実験の範囲内という限定的な条件のもとではあるが,英国人も圧迫感を感じておりその程度は日本人より少ないこと。緑による圧迫感の緩和効果が確認されたこと。などを導き,圧迫感の概念は国境を越えた普遍性を有し,この問題に対処する重要性が示されたとしている。

第6章は,結論に相当し,前章までのまとめを行い,持続可能性のある都市開発には,緑が有する視覚的効果の測定や都市景観における適切な規則を持つことが重要であり,この問題に対する包括的な理解と国際的な研究が必要であると結んでいる。

このように,本論文では,現実の都市景観を対象とした現場実験と要因を制御した実験室実験を通して,都市景観における緑の視覚的効果を定量的に説明したこと。圧迫感の低減について緑の重要性を示したこと。異文化間の比較を行い国際的な観点での研究の必要性を示したこと。など持続可能な都市建築をデザインをするための重要かつ有益な知見を導き出しており,建築学および工学に対する寄与は大きいといえる。

よって本論文は,博士(工学)の学位請求論文として合格と認められる。