城市的間隙建筑
——基礎設施下方棄置空間的再利用

古斯塔夫·安布羅西尼/Gustavo Ambrosini

黃華青 譯/Translated by HUANG Huaqing

“高速公路可能會切斷重要的視覺及符號聯(lián)系：破壞優(yōu)美的景觀，或是切斷區(qū)域之間的心理可達性，如同在觀感上打斷一條習慣性線路或是某種連續(xù)性活動……我們可以采用多種策略將其破環(huán)程度降至最低：控制高架橋的高度，或是重新鏈接從路面上方或下方穿過的結構、活動以及通道”[1]。

重型交通基礎設施疊加在城市形態(tài)之上，形成了一種最容易被忽視的城市空間類型：即城鎮(zhèn)的高架高速公路、地鐵及鐵路線路下方未被充分利用或被浪費的區(qū)域。這些空間對城市使用者很不友好。它們代表了兩種尺度之間的轉變：一邊是人的尺度，另一邊是“空降”在場地上的大型混凝土或鋼鐵構筑物的尺度。這些空間常被認為是衰敗之地，突如其來的黑暗和不間斷的噪音令人感到不安、壓抑乃至焦慮。它們是城市肌理中將街區(qū)或景觀分割的切口。

因此，當今城市面臨的挑戰(zhàn)之一即為如何利用和管理基礎設施下方的公共空間。換言之，即如何真正修復這些空間——不僅是從美學角度，還要將其轉化為有價值的社區(qū)資產。

1 分離/互動

如今，交通基礎設施與城市之間的關系似乎受到一種分離邏輯的統(tǒng)攝：基礎設施基于工程和道路系統(tǒng)的效能準則，建立并傳達其作為自治空間的屬性。道路功能維度從整個城市設計范疇中的分離可追溯至20 世紀初，當時運輸和交通被作為“獨立”科學學科而設立。

從這個意義上說，高架道路或鐵路僅被視為一種依賴自持的原則、由極為有限的建筑語匯庫所規(guī)約的技術性構筑物。大多數(shù)情況下，其形式來自于交通流理論、橫縱面校準、橫截面和交叉道口的幾何構型。但也關乎彎矩與撓度—跨度關系、預制與預應力技術、施工與維護理念等。因此，在對交通網絡進行改造干預時，它們往往被認為是一種無異于水力學原理的簡單更新，從而失去了自身的表現(xiàn)性、象征性和典型性力量。

此外，現(xiàn)代主義運動形成的城市規(guī)劃理念恰恰也遵循了這種分離原則，表現(xiàn)在對工作、居住、休閑和交通四大關鍵職能的定義中：根據(jù)功能主義城市規(guī)劃原則，交通系統(tǒng)的自治性反映了都市機體的抽象功能性理念，這種功能性基于車輛交通、建筑朝向以及土地的自由使用。眾所周知，這條路徑受到了極大的重視。正如勒·柯布西耶曾寫到的，傳統(tǒng)的城市街道——通路——是難以忍受的：他曾公開爭辯卡米洛·西特在1889 年出版的《城市設計》一書中提出的關于“中世紀城市中異規(guī)且曲折的街道的空間及表現(xiàn)潛力”的觀點，嘲諷地將其定義為“馱驢之路”[2-3]。

值得一提的是，在勒·柯布西耶的作品中，道路的意義呈現(xiàn)出一種矛盾特征。在巴黎瓦贊規(guī)劃中，道路的形式存在消隱了，而削弱為一種交通流：人們可以在“寬敞的路面上行駛，道路表面恰當?shù)貏澐譃闄C動車道和步行道”，也可以在“寬敞的公園里散步，遠離公路的嘈雜聲”[4]。相反，在他為一些南美城市和阿爾及爾所做的規(guī)劃中，道路的意義發(fā)生了轉變：作為在更大范圍內出現(xiàn)的一種形態(tài)，道路在城市的秩序系統(tǒng)中被重新定位。類高架橋結構支撐起幾公里長的連續(xù)高架路，契合城市的地理尺度，同時也是可滿足居住及辦公功能的巨構物。勒·柯布西耶在1929 年蒙得維的亞和圣保羅方案中勾勒出的中軸線結構，及1932 年里約熱內盧方案和1933 年阿爾及爾方案中穿越景觀的蜿蜒巨構，均是從鳥瞰視角規(guī)劃項目的結果。這些構筑物相互交疊，同時又從所在環(huán)境抽離?，F(xiàn)存的城市肌理被削弱為一個抽象的背景。幾乎成為悖論的是，在他重塑可居住的高架橋這樣一個強有力形態(tài)時，竟沒有考慮人們如何真正使用基礎設施下方的空間。即使是在最廣為人知的“炮彈計劃”草圖中，盡管他近距離描繪了基礎設施下方的可居住空間，卻也沒有刻意呈現(xiàn)該空間與地面的關系，只見一些仿佛懸浮在景觀之上的陽臺。

1960 年代，諸多項目在這樣的“高架橋”式城市愿景下孕育而生，構想著通過建造超級巨構以塑造大都市的尺度。但在同一時期，多個研究領域中均出現(xiàn)了反對將道路分離的聲音，他們希望強化道路是連接人類活動的途徑這一理念，關注人對基礎設施景觀的感知。

諸多研究中的方向之一，是源于英國雜志《建筑評論》所呈現(xiàn)的文化途徑。其中，西爾維婭·克洛所作的《道路的景觀》（1960 年）一文，表明景觀設計師的工作范圍已從傳統(tǒng)的公園和花園擴展到了流動性空間的尺度：這一趨勢不僅關注如何在不破壞環(huán)境的情況下置入基礎設施，也注重如何塑造基礎設施自身的形象及造型特征[5-7]。另一發(fā)展趨勢來自麻省理工學院和哈佛大學的城市研究聯(lián)合中心，他們重點研究交通基礎設施使用過程中的視覺及感知層面：旨在理解基礎設施的規(guī)模和技術如何重塑環(huán)境中的象征性及表征性結構。出于將觀察者所接收的新視覺材料重新組織的意圖，他們利用視覺形式感知的理論，建立了與運動相關的感知性導則[8-10]。

2 圖像

除學術文獻之外，或許有必要分析幾個現(xiàn)實案例，幫助我們更好地理解與基礎設施“之下”和“之中”的空間相關的形象化潛能，并指出幾個關鍵話題。

1 墨西哥城起義者廣場，薩爾瓦多·奧特加，1969（攝影：古斯塔夫·安布羅西尼）/Plaza de los Insurgentes, Mexico City,Salvador Ortega, 1969 (Photo: Gustavo Ambrosini)

2 洛迦諾公路環(huán)島，奧雷里奧·加爾菲蒂，2001（攝影：古斯塔夫·安布羅西尼）/Locarno roundabout, Aurelio Galfetti,2001 (Photo: Gustavo Ambrosini)

2.1 宜居性：墨西哥城起義者廣場

1969 年，隨著地鐵線路的建造，城市近中心區(qū)的一個主要道路樞紐經歷了徹底的改造和轉型，成為一組立交橋，解放了大面積步行空間（圖1）。由建筑師薩爾瓦多·奧特加設計的這個項目使得在基礎設施下安置商店、酒吧、餐廳和公共服務成為可能，這些設施將朝向內部的步行區(qū)域開放：這是一片生機勃勃的現(xiàn)實綠洲，密布著休息座椅、街邊攤販和樹木。地鐵站位于并不中心的位置，外圍環(huán)繞一道曲墻，墻上點綴鏤空的混凝土砌塊，每個空隙間皆鑲嵌著來自瑪雅文化象形刻版中的圖樣。地鐵站是人流匯聚之處，但所有活動都被安置于立交環(huán)島之下，因此道路才是真正的空間塑造者；然而，車輛交通并未干擾這里的活動，因為它完全被隱藏在一道清水混凝土護墻背后，墻上裝飾了彩繪的護欄。這道護墻持續(xù)彰顯著道路環(huán)島的存在，同時也扮演著廣場“立面”的對應角色。最引人注目的形象并不來自周遭建筑，而是由腳手架結構高高懸掛起來的巨型廣告牌，形成一道由層層疊疊的彩色亮板構筑的風景。

2.2 標志性：洛迦諾公路環(huán)島

這座由建筑師奧雷里奧·加爾菲蒂設計的環(huán)島，建于2001 年，標志了這座城市的高速出口（圖2）。設計意圖是將一處嚴格意義上的技術設施轉變?yōu)橐惶幩叫缘牡貥恕鼞鹾匣A設施的尺度，能夠長期作為這座城市的“門戶”。同時，地段下挖4m 以承載公共及休閑活動（國際電影節(jié)亦在眾多活動之列），并提供不同城市區(qū)域之間的步行連接。內部墻體是由清水混凝土曲面隔斷組成的，按照高低錯落的交替韻律布置。這些要素不僅起到隔音作用，同時也作為綠植的生長地：這一混凝土邊界由此成為一個具有厚度的空間元素，由規(guī)律的虛實序列構成，其中的綠植面向場地內部盛放傾展。這座新“廣場”的極少主義立面構筑起一座垂直花園，它表征了基礎設施的人工性，同時從中建立起一種獨特的表現(xiàn)性語言。這道混凝土環(huán)墻就像是內側環(huán)島邊緣道路的褶皺。這一道鋸齒形的環(huán)墻讓公路上的車行者亦可半遮半掩地瞥見內部空間；同時，它也增強了混凝土這種道路建設典型材料的柔性。該項目強化了這一場所作為高速出口的價值，提出了一種利用基礎設施素材來生成新建筑語言的形象邏輯。

2.3 再自然化：巴塞羅那特立尼塔公園

這座公園于1992 年由恩里克·巴特和胡安·洛瓦設計，位于一個大型交通樞紐——兩條高速路、城市環(huán)路、鐵路和地鐵線在此交匯（圖3）。公園設計為一個同質化的整體，植栽、水體、地形、公共空間和設施都是其整體的一部分。項目從將高速公路部分遮蔽起來開始——通過一個新建停車場和大型架空平臺將周邊社區(qū)連接起來——一系列退臺將不同要素組織起來，其中亦容納了體育設施；這條坡道通往公園的核心區(qū)，緊靠一片半圓形水池。在這個案例中，基礎設施的環(huán)形結構并未被隱藏，而是成為場所地形塑造的基礎；公園中的所有元素都順著這一曲線形式來安排。大片樹叢和水體隨之強化了這一基本形式，同時又消解了公路的重量感。場所的尺度由植物韻律界定，提升了本地植物種類（柏樹、白楊、懸鈴木或果樹），并由高度接近公路的山體所強調出來：在此，視線被成排的白楊引導上升，白楊樹叢圍合而成的柔和曲面也可作為高速公路的屏障。由此，基礎設施成為塑造場所、為新型社會空間賦形的元素，重新將自然和地形引入城市。

這些案例展現(xiàn)了基礎設施的建設如何強烈地與一種城市空間使用觀念相關聯(lián)；但它們也可以為當下某些情境提供詮釋——即除了關注基礎設施的新建，更主要的問題似乎是尋求現(xiàn)存基礎設施再利用的策略。

城市轉型的現(xiàn)象早在1980 年代的歐洲就已浮現(xiàn)在學術討論中——大片工業(yè)用地遭到閑置、土地消耗亟需限制、基礎設施老化廢棄，這極大吸引了人們對于城市邊緣或冗余區(qū)域的再利用問題的關注。諸如再利用、再開發(fā)、回收利用這樣的詞匯，證實了一個如今已在歐洲文化語境下完成的范式轉型，即從基于“新”的概念，轉而認可一個持續(xù)更新現(xiàn)有材料的過程。由此，即便是在土地開發(fā)過程中通常被視為廢料之物——無論是基礎設施還是棄用區(qū)域——都可以成為更新項目的契機：它們借助特定的行動，通常是自下而上的路徑操作，能夠激活城市或區(qū)域中的廢棄機體[11]。

分離和沖突——體現(xiàn)在基礎設施尺度與人體尺度的關系中——證實了城市作為一個由碎片組成的整體的理念，需要一種間隙式的介入過程?！伴g隙”這一概念源于馬丁·布伯的哲學話語，最早于1950年代由阿爾多·凡·艾克引入，用來定義在社區(qū)空間和概念領域之間互動作用的中間區(qū)域[12]。對凡·艾克而言，對間隙的關注意味著調動兩個相鄰的元素，由此達到一種互惠的成效：并不是常見的非此即彼，而是借助其彼此間的張力來創(chuàng)造一個作為第三空間的縫隙。這便是赫曼·赫茲伯格定義為“限閾”之物：“具有不同領域特征的區(qū)域之間的過渡和連接，一個自持之所，它在本質上構建了不同秩序的區(qū)域之間會面和對話的特定情境”[13]。

3 加密/開放：案例研究和策略

3 特立尼塔公園，巴塞羅那，恩里克·巴特，胡安·洛瓦，1990-1993（攝影：古斯塔夫·安布羅西尼）/Trinitat Park, Barcelona, Enric Battle, Joan Roig, 1990-1993 (Photo:Gustavo Ambrosini)

"An expressway may break off important visual and symbolic connections: destroy a fine view, or shut off psychological access between one section and another, as by visually disrupting a customary line of approach, or a continuous linkage of activity…Various devices may be used to minimise the damage:manipulating the elevation of the roadway, or reconnecting structures, activities, and pathways over or under the roadway"[1].

The superimposition of heavy transportation infrastructures on the form of cities produces one of the most common types of neglected urban space:the underutilised or wasted areas below elevated freeways, subways and railway lines inside towns.These spaces are quite unwelcoming for city users.They represent a shift between the human scale and the scale of the large concrete or iron structures"landing" on the ground.They are often perceived as places of decay, where sudden darkness and incessant noise cause feelings of unease and oppressiveness,when not anxiety.They are cuts in the city's pattern dividing neighbourhoods or landscapes.

Therefore, one of the challenges today facing cities is to take charge of public spaces at ground level below infrastructures.In other words, how to really recover them, not only from the aesthetic point of view, in order to transform them into valuable community assets.

1 Separate/Interact

Nowadays the relationship between the transport infrastructure and the city seems to be dominated by the logic of separateness: the infrastructure establishes and communicates its own nature as an autonomous space, derived by engineering and road system efficiency criteria.The isolation of the functional dimension of the road from the overall design of the city dates back to the beginning of the 20th century, when "autonomous"scientific disciplines regarding transport and traffic arose.

In this sense, an elevated road or a railway is intended as mere technical structure that depends on self-referential discipline, regulated by a limited syntax coming from building repertoires.The form derives in most cases from traffic flow theories,horizontal and vertical alignments, cross-section and intersections geometries.But also from bending moment and deflection-span relationship, precast and pre-stressed techniques, construction and maintenance concepts.Hence, when modifying interventions of the transport networks occur, they are often supposed to be a simple update, assimilated to the principles of hydraulics and consequently deprived of their own expressive, symbolic and representative capacity.

Furthermore, it is precisely the conception of urban planning developed within the Modern Movement that follows a logic of separateness, when defining the four key functions – work, residence,recreation and transport: the autonomy of the transport system, as established in the Functional City principles, reflects the idea of an abstract functionality of the metropolitan body, based on vehicular traffic, on the orientation of buildings and on the free land use.As it is well known, this approach had a great emphasis, for example, in the writings of Le Corbusier, in which the traditional city street – the rue corridor – was considered no longer tolerable: he openly argued with the approach that Camillo Sitte proposed in his 1889 book Der St?dtebau, about the spatial and expressive potential of irregular and curving streets in Medieval cities, mockingly defining them as pack donkey's way (the "chemin des ane")[2-3].

It is interesting to remark that in the works of Le Corbusier the meaning of the road takes on an ambivalent character.In Plan Voisin it disappears as a form itself and is reduced to a traffic flow canal:people were intended to drive along "roadways of ample dimensions and a proper division of their surface as between motor-transport and footpassengers" and walk "among spacious parks remote from the busy hum of the highway"[4].On the contrary in the plans for some South American towns and for Algiers it undergoes a shift in its meaning:it appears as being repositioned in the ordering system of the city by acting as a form at a larger scale.Viaduct-like structures perform as continuous elevated roads several kilometres long, in relation to the geographical dimension of the city, and in the meantime as giant buildings that host housing and offices.The straight axes sketched in the proposals for Montevideo and S?o Paulo in 1929 as well as the serpentine mega-structures winding through the landscape of the plans for Rio de Janeiro (1932) and Algiers (1933) are the result of a project conducted from a bird's eye view, which overlaps them and at the same time detaches them from the context.The existing city's patterns are relegated to an abstract background.It almost seems a paradox that the reinvention of such a powerful image, the inhabited viaduct, does not take into account how people would really use the space underneath the infrastructure.Even the most famous sketch of the Plan Obus that closely represents the inhabited spaces below the infrastructure does not intentionally represent the relationship with the ground, leaving the balconies as if suspended above the landscape.

In the 1960s many projects came up from that"viaduct" city vision, envisaging the construction of large mega-structural forms as a generating element of the metropolitan scale.But in the same period,a reaction against that condition of separateness of the road emerged in several fields of study, aiming at enhancing the idea of a road as a mean of connection of human activities, which therefore focused on the human perception of the infrastructural landscapes.

One of these lines of research arose in the context of the cultural approach expressed by the British magazine Architectural Review.There were several contributions, such as The Landscape of Roads by Sylvia Crowe (1960), which showed a widening of the landscape architect's traditional field of work – the park and the garden – to the scale of mobility spaces: this approach focused on how to insert the infrastructure without damage in the environment, but also how to give it its own physiognomy and figurative personality[5-7].Another trend developed from the studies of the Joint Centre for Urban Studies of the Massachusetts Institute of Technology and Harvard, focusing on the study of the visual and perceptive aspects in the use of traffic infrastructures: the purpose was to understand how the scale and the technologies of the infrastructures modify the symbolic and expressive structures of the environment.The intention of re-organising the new visual materials that are offered to an observer led to building an inventory of perceptual principles related to movement, making use of the theories on the perception of visual form[8-10].

2 Figures

Alongside the disciplinary literature, it may be useful to analyse some real cases that help us to better understand the figurative potential linked to the spaces "below" and "inside" the infrastructures,pointing out some key topics.

2.1 Liveability

4 鐵路橋更新項目，蘇黎世，2004-2010（攝影：拉爾夫·胡特）/Im Viadukt, Zurich, 2004-2010 (Photo: Ralph Hut)

5 黃金町中心，橫濱，2012（攝影：工作站）/Koganecho Centre, Yokohama, 2012 (Photo: Workstation)

6 生活方式百貨商店，福爾堡，1998-2002（攝影：漢斯·帕提斯）/Life Style Department Store, Voorburg, 1998-2002(Photo: Hans Pattist)

以下幾個案例的綜述將縱覽多種路徑和策略——從室外休閑空間到容納服務設施及文化活動的新體量。在某些案例中，這些策略的目的是提升空間密度，嵌入功能和體量，提出與基礎設施相抗衡的形式和材質，在完善與地面的連接的同時，將它們從抬高的道路及視線中脫離開來，以確認其自身的材料自治性。相反，其他的案例則呈現(xiàn)了一個清空和重塑場地的過程，將自然重新帶回城市，開辟了順沿或穿越基礎設施的路徑以作為城市的慢行空間，加強它們作為帶頂?shù)氖彝饪臻g的獨特屬性。

加密的路徑可以借助多種表達性策略來實現(xiàn)。

2004 年，EM2N 建 筑 事 務 所 與Zulauf Seippel Schweingruber 景觀建筑事務所贏得了一項建筑競賽，是針對瑞士蘇黎世一座19 世紀鐵路橋遺產的修復更新（圖4），這座橋曾割裂了一片成熟的住宅區(qū)和一片老工業(yè)區(qū)。設計挑戰(zhàn)是如何將一座受保護的遺產重新納入城市系統(tǒng)的一部分來使用。它由兩條交匯軌道組成：較低的一條軌道被改造為一條自行車及人行道，較高的一條則繼續(xù)用作鐵路。在兩條軌道之間的三角區(qū)域建造了一座新建筑，以容納大約30 間商店、小餐館和一家雜貨市場。這座建筑建于2010 年，它是一組由三元乙丙橡膠覆蓋的體量，分成一系列上下起伏、擁有圓形天窗的單體建筑；支撐體系采用預制木架結構，一體化的膠合板木格架體系固定在兩層鋼格柵構件之間。屋頂翻折的韻律順應橋梁拱券的節(jié)奏，視覺上仿佛連接了兩座高架橋：新建筑就像是拱券之間的帶狀商店，刻意的形式約束凸顯出宏偉的石柱結構。這樣的建筑選擇表達出高架橋模棱兩可的屬性：既是一座超大尺度的連接器，又是一座線性的公共建筑。

日本橫濱的黃金町歷史上曾是非法犯罪活動的集聚地，在21 世紀最初10 年的一項城市更新計劃中經歷了深度轉型（圖5）。2008 年以來，黃金町區(qū)域管理中心、一家當?shù)胤菭I利性組織、橫濱市政府以及九州島鐵路公司開啟了一項合作，試圖以公共事件及藝術活動為契機，推動社會的再發(fā)展。2012 年，一片大約100m 長的鐵路橋下土地被徹底更新，容納了一家畫廊、一間咖啡廳、一座圖書館、一間藝術家工作室、一處會面場所，還有一塊擁有階梯座位的帶頂廣場。設計工作委托了7 家建筑事務所共同完成，包括Contemporaries, Studio 2A, SALHAUS, Workstation, Koizumi Atelier,Sogabe Laboratory-Matidesign, Nishikura Architectural Design Office：每家都借助不同的形式語言以及木材、玻璃和素混凝土等簡單材料，與現(xiàn)存的厚重混凝土柱建立了各自的對話。最終的設計結果呈現(xiàn)出一種折衷的多樣性，當人們漫步其間，能夠激發(fā)一種充滿活力的感受；同時，洗練的建筑體量維持了整體上的感知一致性，吸引社區(qū)居民來使用這些失而復得的空間。

在荷蘭沃爾堡，NIO 建筑事務所為“生活方式”百貨商店設計了一座新建筑，建筑位于一座公路鐵路雙線高架橋的下方（圖6）。建筑體量占據(jù)了高架橋下約50m 的全部進深空間，并在端部懸挑至室外。建筑側面采用大跨度的不規(guī)則拱結構，表面覆蓋小塊玻璃馬賽克：在南端，建筑結構凸出至高架橋外，懸挑在公園前的一塊步行區(qū)域上，形成了巨大的入口雨棚。建筑室內是一個大空間，采用白色天花和黑雜色混凝土地面，其中陳列著五彩斑斕的各品牌服裝、鞋履、配飾和化妝品。這是一個彎曲的、近似動物形態(tài)的形式，與它并置的是高架橋的筆直線形：厚重的拱形體量幾乎是紀念性的，它也在體量上與上方橋梁的巨大尺度形成對比。同時，圓潤的外形和綠色瓷磚的多種細膩色差——配合櫥窗的垂直木分隔——使它成為一個“柔軟”的客體，具有極大的觸覺表現(xiàn)力，陪伴著路過的行人。

7 斯坦尼加S2劇場，日利納市，2009（圖片來源：斯坦尼加檔案館）/S2 Theatre Truc Spherique, Stanica Zilina, 2009(Source: Stanica archive)

Plaza de los Insurgentes, Mexico City.In 1969,during the construction of the metro line, one of the intersection of the main avenues in a semi-central area of the city was completely remodelled and transformed into an elevated road junction that freed up a large space for the pedestrians.The project by architect Salvador Ortega made it possible to locate shops, bars, restaurants and public services under the infrastructure, open towards the inner pedestrian area: this is a real oasis of liveliness, with crowded benches, street vendors and some trees.The subway station is located in a non-central position and is characterised by a curved wall lined with concrete hollowed-out blocks, each one containing pictograms inspired by the stone carved glyph boards of the Maya culture.The station is a hub of pedestrian flows,but the activities are all placed under the avenue ring,so it is the road here that really shapes the space;however, the vehicular traffic does not disturb its activities, as it is almost completely hidden by the exposed concrete parapet crowned by a painted guard rail.That parapet is the continuous mark revealing the presence of the road ring and acts as a counterpoint to the "fa?ades" of the square.The prevailing image is not given by the architecture of the surrounding buildings, but by the giant advertising signs hanging on them with their structures, that form a scenery of overlapping coloured and shining surfaces.

2.2 Iconicity

Locarno highway roundabout.The roundabout designed by architect Aurelio Galfetti, completed in 2001, marks the arrival point of the motorway in the city.The intent was to transform a strictly technical element into a horizontal landmark – related to the scale of the infrastructure – capable of perceptually acting as a "door" to the city.At the same time, the site is excavated 4 metres lower than the road level to host public and entertainment activities (among various events, the International Film Festival) and provides a pedestrian connection between different urban areas.The internal walls are made up of curved partitions in exposed reinforced concrete, arranged according to an alternate sequence of high and low walls.These elements constitute a noise protection wall but at the same time they act as a support for the vegetation: the concrete edge becomes a thick element, consisting of a regular sequence of solids and voids, which incorporates the plants, shows them outwards and pours them out into the inner space.The minimal language of the fa?ade of this new "square" constitutes a vertical garden which expresses the artificiality of the infrastructure and builds a specific expressive language from this.It is as if this concrete profile constituted a corrugation of the road along the edge of the inner ring.A builtup crenellated wall protects but allows motorists to glimpse the interior space; at the same time, it enhances the plasticity of concrete, a material typical of road construction.The project emphasises the value of the place as the arrival point of the highway,proposing a figurative logic that uses the materials of the infrastructure to generate a new syntax.

2.3 Re-naturalisation

Trinitat Park, Barcelona.The park was built in 1992 on a project by Enric Battle and Joan Roig and is located within a large circular interchange where two motorways, the city's ring road, the railway and the subway converge.The park is designed as a homogeneous entity, in which vegetation,water, orography, public spaces and facilities are part of a whole.Starting from the covering of a part of motorway – which allows to connect the neighbouring district through a new parking lot and a large terrace-bridge – a series of terraces arranges the various essences, hosting sports services; this sloping course leads to the heart of the park, bordered by a semi-circular water basin.In this case, the circular sign of the infrastructure is not hidden, but rather constitutes the foundation trace that establishes the topography of the place; all the elements of the park are put in place following this curvilinear pattern.The large plant masses and the water system consequently underline this foundation mark, counterbalancing at the same time the visual weight of the roads.The scale of the place is marked by vegetation rhythms,enhancing local plant species (cypress, poplar, plane,or fruit trees) and emphasised by the hill that reaches the level of the highways: here the view is directed upwards by the rows of poplar trees creating gentle arching lines and acting as screen for the freeway.Infrastructure can thus be the element that shapes the place and gives form to new social spaces,reintroducing nature and orography into the city.

These are examples in which the construction of the infrastructure was strongly connected to a concept regarding the use of urban space; but they can offer some interpretations in present time when,rather than the construction of new infrastructures,the main question seems to be the setting up of strategies for recycling the existing ones.

The phenomena of urban transformation that were already emerging in the debate of the eighties in Europe – the dismissing of vast industrial areas, the need to limit land consumption, the obsolescence of infrastructures – had progressively drawn attention to rehabilitation issues envisaged for marginal or residual areas of the city.Terms such as reuse, redevelopment, recycling testify to the now completed paradigm mutation, in the context of European culture, from a concept based on the idea of the "new", to an awareness of the process of continuously remodelling existing materials.In this sense, even what is commonly considered the waste of a territorial development process – whether they are infrastructures or abandoned areas – could become an opportunity for regeneration projects: by means of specific actions, often carried out according to bottom-up interventions, able to innervate the obsolete body of cities and territories[11].

Separateness and conflict, expressed by the relationship between the infrastructure scale and the human scale, certify the idea of the city as a complex made up of fragments that requires an in-betweening process.The "in-between" concept, taken from Martin Buber's philosophy of dialogue, was introduced by Aldo van Eyck in the 1950s, to define intermediate zones that interact between communicating spatial and conceptual areas[12].For Van Eyck, to drive attention to the in-between means employing two elements in conjunction so that to obtain a reciprocal effect: it is not the prevalence of one over the other,but their mutual tensioning to create a gap as a third space.It is what Herman Hertzberger defined with the term "threshold": "the transition and connection between areas with divergent territorial claims and,as a place in its own right, it constitutes, essentially,the special condition for the meeting and dialogue between areas of different orders"[13].

3 Densify / Open: Case Studies and Strategies

A review of several projects offers an overlook of several approaches and strategies, from outdoor leisure spaces to new volumes for facilities and cultural activities.In some cases, these are strategies that densify the space, adding functions and volumes,proposing shapes and materials that counterpoint the infrastructure, complete its connection with the ground but at the same time detach themselves from the elevated track from the perceptual point of view,affirming their own material autonomy.In other cases, it is, on the contrary, a process of emptying and re-modelling the ground, which brings nature back into the city, which promotes paths along or through the infrastructure, as places of slow journey within urban space, enhancing its uniqueness of covered exterior space.

The densifying approach can be carried out by means of multiple expressive strategies.

最后是斯洛伐克日利納市的斯坦尼加文化中心S2 劇場，這個案例絕佳地表達了將高架路下方的消極空間轉化的回收策略（圖7）。非盈利組織“Truc Spherique NGO”此前就曾將臨近一座仍在運行的火車站更新植入了多媒體的文化活動。2009 年，該組織建造了一座用于戲劇表演和公共活動的社區(qū)空間，建筑是由120 名志愿者在3 個月內建成的，由土草建造體系專家湯姆·萊文指導。這兩座相交的圓柱體嵌入高架路之下，墻體由3000 個啤酒箱組成，填充物是混入干草的粘土；建筑入口是嵌入圓柱體基礎部分的一個藍色集裝箱。建造過程同時是一項完全采取可回收地方材料及廢品的實驗性工程，無需任何復雜技術。不幸的是，這座建筑在10年后因火災嚴重損毀。

另一類建筑策略試圖將場地重塑為宜居的城市通道，也提出了多樣化的休閑功能。

在美國的某些實驗案例中，這類通常在城市擴張中殘剩的棄置空間的再利用，最先是由一些面向滑板、自行車等青年非主流運動的自組織團體發(fā)起的。例如，波特蘭的伯恩塞德滑板公園（圖8），是在1990 年由一群滑板青年在未經允許的情況下建造的，他們“重新收復”了這片曾經為癮君子和賣淫者所統(tǒng)治的區(qū)域。項目一開始只需將混凝土澆筑在墻體邊以形成堤岸，然后慢慢塑造出現(xiàn)代滑板公園所需的隆起、下凹、塔尖、垂面等地形特征。這個公園未從城市官方得到任何贊助，但借助著志愿者和捐獻者的付出，它成為一個名副其實的公共空間，得到當?shù)厝说膹V泛接受和歡迎，被視為城市景觀活力的杰出案例。

西雅圖的“I-5 柱廊”項目也經歷了一個類似的轉型過程。20 世紀之交，這塊位于市中心北部I-5 高速公路下方坡地的廢棄區(qū)域，吸引了一個當?shù)刈孕熊嚿缛旱淖⒁猓弧班l(xiāng)野自行車越野俱樂部”于是被引進至此，借助資助、贊助和捐助建造起一座自行車公園，于2008 年建成。在高速公路巨柱之間蛇行穿梭著自行車道、越野道以及遛狗區(qū)，如今已成為自行車運動的熱門場地，吸引著專業(yè)運動員、初學者和家庭出行者。

滑板或自行車運動者對空間的使用與常規(guī)的城市使用之間的潛在矛盾亦不可低估：空間的塑造必須讓滑板的空中騰躍等最具“攻擊性的活動”與兒童老人等使用者的需求毫無危險地共存。SCOB 建筑與景觀事務所在巴塞羅那設計的兩個項目，就致力于將滑板公園塑造為城市街道的公共場所，與城市景觀緊密互動。

奧萊亞—夸德拉多城市運動公園被設計為一個滑板廣場，提供了一處基礎設施高架下方的連續(xù)公共場地（圖9）。直線元素根據(jù)某種分段式肌理而彎折，伴隨著景觀的重整，塑造出傾斜的人工及自然表面。高差變化和連續(xù)坡道加強了場所的連續(xù)感，滑板的要素序列與植物相融合：墻體、傾斜表面、臺階、臺地、平臺、座椅、扶手等皆由混凝土和耐候鋼板建造，共享同一種語言。

9 奧萊亞—夸德拉多城市運動公園，巴塞羅那，2014（攝影：安德瑞亞·古拉）/Aureà Cuadrado Urban Sports Park,Barcelona, 2014 (Photo: Adrià Goula)

10 巴羅—德韋維爾城市體育公園，巴塞羅那，2016（攝影：安德瑞亞·古拉）/Baró de Viver Sports Urban Park,Barcelona, 2016 (Photo: Adrià Goula)

8 伯恩塞德滑板公園，波特蘭，1990（攝影：泰德·恩斯特·薩爾維塔）Burnside Skatepark, Portland, 1990 (Photo: Ted Ernst Sarvata)

In 2004, the bureau EM2N architects and Zulauf Seippel Schweingruber Landscape Architects won the architectural competition for the refurbishment of a XIX Century monumental train viaduct in Zurich,Switzerland, separating the developed residential area from the old industrial district.The challenge was to re-use a protected monument as part of the urban system.There were two converging tracks: the lower was transformed into a cycle-pedestrian path,the higher kept its railway use.In the triangle space between the rail tracks, a new building took place, in order to host around 30 shops and cafés and a market hall for groceries.It has been completed in 2010 as a folded volume covered with black EPDM rubber, made of a series of rising and falling segments punctuated by roof-light domes; the supporting framework is made of pre-fabricated timber panel elements with integrated glue-laminated timber brackets, clamped between steel lattice elements.The rhythm of the roof folds follows the rhythm of the arches and visually interlace the two viaducts: the new structures appear as band-like shopfronts between the arches,deliberately restrained so that to emphasise the giant stone pillars.The architectural choices express the ambivalent character of the viaduct: a large-scale connecting machine and a linear public building.

The district of Koganecho in Yokohama, Japan,historically devoted to illegal activities, was deeply transformed through an urban renewal plan in the first decade of the 21st century.Since 2008, a collaboration was started between Koganecho Area Management Centre, a local non-profit organisation,the City of Yokohama and the Keikyu railway company, in order to foster events and art activities as an opportunity for social re-development.In 2012,an about 100 metres stretch of land under a train overpass was completely transformed to host an art gallery, a café, a library, an artist's atelier, a meeting space and a covered piazza with stepped seats.The work was commissioned to seven architectural offices(Contemporaries, Studio 2A, SALHAUS, Workstation,Koizumi Atelier, Sogabe Laboratory-Matidesign,Nishikura Architectural Design Office): each of them has established their own dialogue with the concrete thick existing columns, by means of different shapes and simple materials – wood, glass, metal and pale concrete.The overall result expresses an eclectic multiplicity, generating a dynamic feeling as people walk along and through the complex; at the same time, the clean-cut volumes maintain an overall perceptual coherence, welcoming the community to utilise the regained space.

In Voorburg, the Netherlands, NIO Architecten designed a new building for the Life Style Department Store under a double viaduct carrying motorway and railway tracks (1998-2002).The volume occupies the entire depth of the viaduct, about 50 metres, and continues outside with curvilinear ends.The sides are made up of large irregular arches covered with small glass mosaic tiles: at the southern end, this structure literally juts out from the viaduct, overhanging a pedestrian area in front of a garden and forming a large entrance canopy.The interior is one large space with white ceilings and black-pigmented concrete floor, where colourful brands of clothing, shoes,accessories and cosmetics are displayed.It is a curved,nearly zoomorphic form, which is juxtaposed with the straight lines of the viaduct: the dimension of the thick arches, almost monumental, compare in scale with the large size of the bridge above.At the same time, the rounded profile and multiple green colour variations of the tiles – counterpointed by the vertical wooden partitions of the shop windows – make it a"soft" object, of great tactile expressiveness, which accompanies pedestrians as they pass.

Finally, the S2 theatre built for Stanica Cultural Centre in Zilina, Slovakia, represented an outstanding example of recycling strategies to convert inhospitable areas below the road overpass.The non-profit organization Truc Spherique NGO had previously regenerated a nearby still operating railway station for multi-media cultural activities.Then in 2009, this NGO set up the building of a community space for theatre and events through a collective work carried out by 120 volunteers in three months, following the teaching of Tom Rijven, an expert of working systems with clay and straw.Two intersecting cylinders, whose walls were made of three thousand beer crates, filled with straw mixed with clay, were inserted under the motorway bridge; the entrance was provided by a blue shipping container wedged at its base.The building process consisted of experimental work with fully recyclable local material and waste, that didn't need any kind of sophisticated technology.The structure was unfortunately seriously damaged by fire 10 years later.

The strategies aiming at the requalification of the ground as a liveable urban path propose multiple leisure functions.

In some experiences in the USA, the first step towards the reuse of these derelict spaces, considered leftovers in ordinary city growth, was taken by selforganised communities dedicated to youth and nonconventional sports, such as skateboarding or bike.The Burnside Skatepark in Portland, for instance,was created without permission in 1990 by a group of skaters that "re-conquered" an area once overrun with drug addicts and prostitutes.It started by simply pouring some concrete against a wall to make a bank,till reaching the modern skate-park features required as hips, pools, pyramids, and vertical sections.It received no funding from the city, but thanks to the commitment of volunteers and donors it has become a veritable public place, well established and accepted by the locals, perceived as an exemplary case of the vitality of the urban landscape.

The so-called I-5 Colonnade in Seattle underwent a similar transformation process.The dead zone located on a slope under the I-5 freeway north of downtown had drawn the attention of a community of local bikers at the turn of the past century; the Backcountry Bicycle Trails Club was then brought in to build a bike park thanks to grants, sponsorship deals and donations, which was completed in 2008.The winding series of bike paths, trails and an offleash area running under the high motorway columns is now a very popular place for bike activities, used both by expert free-riders and by beginners and families.

The potential conflicts in the use of space between skaters or bikers and the ordinary city users is not a matter to be underestimated: the space must be shaped so that the most "aggressive activities",such as jumping and twirling in the air with a skateboard, can coexist without danger with the needs of other users such as children or the elderly.Two realisations in Barcelona from SCOB Architecture& Landscape office aimed at the creation of skate parks as city street public areas, strictly interacting with the urban landscape.

Aureà Cuadrado Urban Sports Park (2014)is conceived as a skate square that provides a continuous public ground under some elevated infrastructure tracks.Straight lines bend according to a pattern of segments and accompany the modelling of the landscape, shaping inclined artificial and natural surfaces.Changes in level and retaining slopes strengthen the feeling of a continuous place,where the sequence of skate elements blends with vegetation: walls, inclined planes, stairs, steps,platforms, benches, handrails, made by concrete and Corten steel, share a common language.

巴羅—德韋維爾城市體育公園建在特立尼達公路樞紐東部的一塊剩余區(qū)域（圖10），它被鐵道與現(xiàn)有公園分隔開來：在周邊居民看來，這個棄置空間是不安全的，它是速度規(guī)則和公路交通尺度的直接結果。由于道路樞紐的存在，交織的大尺度曲線元素將空間切開，這也成為滑板道的幾何構形的靈感來源?；逭咴诓煌氖覂拳h(huán)道上滑行，伴隨著車輛和基礎設施的曲線運動，在某種程度上將后者融入體育運動實踐。特定的元素——如所謂的“起伏道”“彎曲壽司盤”“鬣蜥尾”等，也被引入以塑造這座新滑板公園的個性特征。在這些項目中，諸多新元素的設計構建了一套獨具識別性的特定視覺語言，同時處理了與基礎設施及景觀元素的互動關系：質地、圖樣、色彩共同形成一套與現(xiàn)存道路和植被相勾連的句法系統(tǒng)。它們不是分離的運動區(qū)域，而是街景的一部分，激發(fā)不同城市使用者之間的互動。

在更大尺度上，某些實驗案例展現(xiàn)了高架基礎設施下方場地的再利用如何促進了線性公園的形成，它們意圖作為一種綠色基礎設施，能夠激活大范圍的城市區(qū)域，支撐新的公共生活形式；同時，它們也印證了公私合作過程的復雜機制。

加拿大多倫多市正在進行一項再開發(fā)計劃，面向的是加德納高速公路下方1.6km 長的廢棄土地，項目設計者是城市設計師肯·格林伯格與公共工程景觀建筑事務所（圖11）。設計方案的構思和形成經過了高強度的、環(huán)環(huán)相扣的多方咨詢過程，參與者包括周邊居民、潛在使用群體、多倫多城市理事會、項目支持者等，還特地成立了一個非盈利獨立慈善機構“彎道守護者”來管理該項目的實施。長約600m 的第一階段工程在2018 年完工。一條新的人行和自行車道穿梭在支撐高架橋的厚重混凝土梁柱序列之間；其中一些柱子高達15m，提供了紀念性的開放“房間”；其他一些柱子則界定出更親近尺度的空間。高架橋之下的空間轉型為一個由景觀化的公園和公共藝術作品構筑的連續(xù)公共場地，提供了多樣化事件與活動的靈活場地；而對坡地的重塑以及棄置泥土的再利用則創(chuàng)造出新的地形。這項共享的公共場地的新模式，為臨近湖岸的多倫多市民提供了一處充滿活力的聚集場地。

一個類似過程也發(fā)生在邁阿密。非盈利組織“橋下之友”與邁阿密戴德郡政府合作，提出一項計劃以改造一段約16.09km 長的鐵路軌道下方，485,622m2的未充分利用的空間。這段軌道是于1984 年投入使用的雙軌高速鐵路系統(tǒng)，穿過城市中心運行（圖12）。詹姆斯—科納—菲爾德景觀設計事務所做了概念規(guī)劃，設想了一條可持續(xù)、多模式廊道，以呈現(xiàn)南佛羅里達的藝術、文化和植被。第一階段建設是北部一條0.8km 長的地段，名為“布里克爾后花園”，于2021 年2 月完工。其設計理念是作為一系列室外的“房間”，每個都有獨一無二的個性：“河流廳”擁有欣賞邁阿密河的景觀視野；“健身房”是由體育場地組成的休閑空間；“散步道”則是一條行人和自行車道，中途穿插面向社區(qū)的空間，如一塊演出廣場，還有一張15m 長的社區(qū)餐桌；“雞蛋石廳”是一塊擁有4 個蝴蝶花園的自然化區(qū)域。新的橋下空間被設計為一個連續(xù)的大尺度社區(qū)公園，同時也在其各個部分提供了一種態(tài)度統(tǒng)一卻又適于各自地段的解決方案，以適應和反映獨特的社區(qū)情境。

11 彎曲之路，多倫多，2018（攝影：尼克·勒胡斯）/The Bentway, Toronto, 2018 (Photo: Nic Lehoux)

12 橋下之友，邁阿密，2021（攝影：羅賓·希爾）/T he Underline, Miami, 2021 (Photo: Robin Hill)

4 結語

最后，這里必須引用一份由紐約公共空間設計信托與紐約市政府交通局聯(lián)合開展的研究。研究的出發(fā)點是意識到，在紐約市共有數(shù)以萬計未充分使用的公共空間，位于共1126.54km 長的高架路之下?；诖嗽掝}而開展的專門研究，試圖理解如何通過回收利用高架交通基礎設施相關的空間來提升社區(qū)韌性。研究報告發(fā)表于2015 年，題為《高架之下：收復空間，鏈接社區(qū)》，提供了此類空間轉型利用的設計提案以及功能與政策建議：包括紐約市橋下土地的詳細目錄、地塊物質環(huán)境的編目、不同場地的參與式工作坊、為具體地段定制的裝置、基于文脈的設計以及功能設置的建議[14]。

總而言之，上述案例研究提供了針對基礎設施沿線下方的未使用空間再開發(fā)的多種設計策略。原本廢棄的場地、空置的土地、現(xiàn)代性的殘余，如今都能經由意義的轉換以吸引公眾的注意，同時也是對城市居民群體的自發(fā)活化。因此，這類空間極其適合轉變?yōu)闀嫦嗑?、社會交往和集體共享的場所。□

The Baró de Viver Sports Urban Park (2016) was built within a residuary area in the eastern part of Trinidad road junction, separated from the existing park by the railway line: it was an abandoned space that neighbours perceived as unsafe, a direct outcome of speed rules and motorway traffic scale.The presence of the highway junction, which cuts through the space with large intertwined curved gestures,served as inspiration for the general geometry of the skate track: skaters move by recreating different interior circuits, which accompany the curvilinear movement of cars and infrastructures, incorporating them, in a certain way, into sports practice.Particular elements – such as the so-called pump track, curved sushi plate, iguana tail – are introduced in order to give personality to the new skate park.In these projects the design of the many elements establishes a specific visual language, with its own identity, but which settles a mutual relationship with the elements of the infrastructure and the landscape: textures,patterns, colours generate a syntactic system connecting with the existing routes and vegetation.They are not separated sports areas but part of the streetscape, encouraging the interaction between different city users.

At a larger scale, some experiences show how the reuse of the ground under high infrastructure has been driven to the creation of linear parks, intended as green infrastructures able to innervate wide urban areas, supporting new forms of public life; they testify as well the complex set up of public-private partnerships processes.

In Toronto, Canada, a redevelopment process of a mile-long stretch of neglected land under the Gardiner Expressway is underway, according to the project of the urban designer Ken Greenberg and the landscape architecture firm Public Work.The design vision and the programming approach were developed through an intense and articulated phase of consultations with neighbours, potential user groups, City of Toronto boards, supporters, and the creation of a not-for-profit independent charity,Bentway Conservancy, in charge of carrying out the project.The first stretch of about 600 metres has been completed in 2018.A new pedestrian and bicycle trail runs between the dense series of supportive portals made by heavy concrete columns and beams; some of them reach the height of 15 metres, providing monumental open "rooms", others define more intimate spaces.The underside of the motorway is transformed as a continuous public ground made of landscaped gardens and public artworks, providing flexible spaces for a multiplicity of events and activities; the remodelling of the slopes, reusing displaced soil, establishes a new topography.This new model of shared public terrain offers a vibrant gathering place for Toronto's population close to the lakeshore.

A similar process is ongoing in Miami.The non-profit association Friends of the Underline, in partnership with Miami-Dade County, envisaged the programme for the transformation of 120 acres of underutilised space below a 10-mile portion of Metrorail, a dual track rapid-transit system that opened in 1984 and runs through the city's urban core.James Corner Field Operations designed a framework plan envisioning a sustainable multimodal corridor inspired by the arts, culture, and flora of South Florida.The first phase regarded a halfmile stretch in the northern part, named Brickell Backyard, and was completed in February 2021.It has been conceived as a series of outdoor "rooms",each one with its own identity: the River Room with views of the Miami River; the Gym, a recreation space with sports courts; the Promenade, a walkway with pedestrian and bicycle paths punctuated by community-oriented spaces, such as a performance plaza and a 50-foot-long communal table; the Oolite Room, a naturalised area with four butterfly garden.The new Underline is designed as a continuous large scale neighbourhood park, offering in each section, at the same time, a common attitude and a site-specific solution able to adapt and reflect specific community issues.

4 Conclusion

In the end, a study by New York Design Trust for Public Space, together with the NYC Department of Transportation, must be cited.The starting point was the awareness that, in the city of New York, hundreds of thousands square metres of underutilised public space are lying under 700 miles of elevated infrastructures: the carrying out of specific research on this topic was aimed at understanding how to increase the resiliency of neighbourhoods by reclaiming the spaces associated with elevated transportation infrastructure.The study released in 2015, Under the Elevated:Reclaiming Space, Connecting Communities, offered design recommendations as well as programming and policy proposals to envisage the transformation of such areas: it included an inventory of land under NYC's bridges, categorisation of physical conditions,participatory workshops at different sites, sitespecific installations, context-specific design and programming recommendations[14].

To conclude, the case studies cited offer multiple design strategies aimed at the redevelopment of unused spaces along and under the infrastructures.Formerly waste areas, vacant lands, leftovers of modernity, now can undergo a reversal of meaning in order to bring about public attention, as well as the spontaneous activation of urban populations.Therefore, they are spaces susceptible of becoming places of meeting, social communication and collective sharing.□