新型城市設計？香港極端城市布局的啟示

作者：Alain Chiaradia (alainjfc@hku.hk)

張靈珠 (zhanglz@hku.hk)

Authors: Alain Chiaradia (alainjfc@hku.hk)

Lingzhu Zhang (zhanglz@hku.hk)

Institution of the Authors: Department of Urban Planning and Design,Faculty of Architecture, The University of Hong Kong

新型擁擠

中國各主要城市正積極新建和擴張地鐵系統，改善交通可持續性，減少快速機動化對環境和社會造成的負面影響。在中國，33個城市設有地鐵線網，另有16個城市的地鐵系統在建，還有不少城市的地鐵線路正處于規劃和提議修建階段。隨著越來越多的人選擇地鐵作為日常出行的工具，以往只存在地鐵車廂內的擁擠問題，現已普遍存在于很多地鐵站廳和連接車站的通道內。

這一新型的擁擠現象并非中國特有。該現象同樣存在于紐約、倫敦、巴黎等多個城市。這是城市設計還未準備好應對的新型城市狀況。大多數城市設計理論側重于增加城市活力，以及增加行人活動。而有關相反現象—活力過旺—的城市設計文獻和項目則少之又少。然而，鑒于擁擠已成為感性和客觀存在的現象，我們認為城市設計可以在理解如何配置逐步多樣化的城市擁擠方面發揮重要作用。

有組織或逐步的分散如何成為一種行之有效的城市設計策略？

這里所說的并非是人群管理—即重大事件舉行時對人的運動和行為的管理，這個有專門的技術和文獻。某項事件的舉行對某時某地造成的擁擠相對有限，而場所的擁擠或多或少具有時空連續性。擁擠導致人開始避開人群密集和人流量過大的場所。設計漸進式活力是讓活力在限定的水平范圍內增長和擴張。設計漸進式活力需要理解某個地方什么時間以及為什么會受到過度的人流強度和活力的壓力。

取經香港？

香港是一個極端配置的城市，是極端地形、氣候、體制、發展歷史和城市創新的獨特混合。受陡峭地形和水域的影響，香港只有20%的土地坡度低于1:5。就是在這復雜的地形條件上，建成了一個超高密度城市，有著極其成功的以公交為導向的開發（TOD）體系，水域、綠墻般的山體、超高密度、軌道交通和道路基礎設施形成了香港獨特絢麗的城市景觀。

香港是世界上擁有最復雜的TOD系統的城市之一。其公共交通系統屢獲贊譽，公交通勤占總通勤的90%被反復提及，這幾乎是其他城市無法企及的鉑金版的可持續交

通標準。但香港仍是一擁擠的城市，地鐵車廂內、地鐵站和地鐵站周邊的建筑綜合體內高度擁擠。有時，許多街道上甚至都會出現擁擠。香港又有哪些關于擁擠、城市形態和城市設計方面的經驗可供我們借鑒呢？

這是否意味著香港能夠成為我們學習的范例？了解超級擁擠是如何形成的，對我們設計緩解措施會起到怎樣的幫助？人們常常會說“香港土地稀缺”，準確的說法應當是“香港平坦和適宜建筑的土地十分稀缺”。因此，香港模型較適用位于低山丘陵地區的城市，而由于多數大城市地勢較為平坦，香港的空間解決方案可能并不適用。

這是否意味著香港能夠成為我們學習的范例？了解超級擁擠是如何形成的，對我們設計緩解措施會起到怎樣的幫助？人們常常會說“香港土地稀缺”，準確的說法應當是“香港平坦和適宜建設的土地十分稀缺”。因此，香港模型較適用于山地城市，而由于多數大城市地勢較為平坦，香港的空間解決方案可能并不適用。

盡管如此，我們可通過從不同方面分析香港如何應對空間局限性，深入了解擁擠現象及其與城市形態的關系，和如何管理擁擠，從中獲得啟示。在本文中，我們主要概述香港極端布局的特點，如果我們了解極端布局與擁擠的關系，我們或許能夠知道如何設計“多樣化”或“漸進式”的擁擠，從而可能得出一種轉移式的緩解城市擁擠的方法。本文下面部分通過對香港擁擠狀況和城市布局關系的反思和分析探討了城市擁擠在不同尺度層面的一些經驗教訓。有關分析中使用的工具和方法的討論亦列于下文。

啟發1:緊湊并非造成擁擠的前提條件

為弄清緊湊是否是造成擁擠的前提條件，我們在深入觀察局部前，首先觀察香港的整體城市形態，包括地鐵和公交線路網、綠色空間的構成、分布和布局，希望弄清上述因素與擁擠的關系。

在城市形態的討論中，針對緊湊和蔓延的問題尤其突出，猶如完全對立的兩個方面。在探討這個問題的時候，不妨讓我們先問個問題，“香港是緊湊型城市嗎？”如果從地域范圍來看，答案是否定的。香港是個垂直發展的城市，人均占用土地極少；香港雖然是極高密度的城市，但這并不意味著它就是緊湊型的城市。當然，香港也并非典型的蔓延型城市。雖然對城市蔓延并無明確定義，但它通常至少具備三個特點：低密度、分散式的非連續性分布和依賴私家車出行。

緊湊型指密集、緊湊，與分散和非連續性截然相反。我們會直觀地將圓形或方形視作緊湊型。如果我們希望通過量化指標評估，我們可以用景觀研究的形狀指數。圓形的緊湊指數為1，方形的緊湊指數為1.27（圖01-形狀指數）。仔細觀察香港的城市形態，不難發現由地鐵線路和嚴謹設計的公路基礎設施連接起來的帶狀發展態勢。香港的形狀指數為83，遠達不到緊湊型城市形態的標準（圖02）。除九龍的極少數地區外，香港的城市形態不具備緊湊型城市的特點。從整體來看，香港的城市形態是多條獨立條帶狀發展形成的組合，這些條帶由陡峭的山體或山體與河流分隔而成。香港的密度剖面圖，即從城市中心向外的（居?。蜆I）密度橫截面與大多數城市不同，大多數城市的市中心更為稠密，由中心向外或多或少呈逐漸遞減趨勢。對于香港而言，其密度分布呈驟升驟降的趨勢，密度為“零”處是水域或城市公園。香港的城市密度呈現高度的峰值化特點，但波峰的數量卻大大減少了。

香港的例子表明，從“城市化連續性”的意義上說，整體城市形態的緊湊并非造成擁擠的前提條件。實際上，緊湊型城市布局可能會緩解擁擠。

啟發2：大型城市公園式的布局可能是造成擁擠的推動因素

如果香港不屬于緊湊型城市，那么地鐵和公路連接的高密度條帶區之間的區域又被作何使用？這些區域包括丘陵林地、灌木叢和草地，約占香港地域面積的65%。因而，香港可謂是一個處在山地公園之中的高密度城市。在多數其他城市，這些區域將是平坦的土地，大多用作城市建設區，其間點綴著綠地和公園。香港卻與之相反。不少城市自詡擁有大片公園/綠地，但未提及這些綠地大多分布在建成區外圍。從城市密度最高的部分來看，這些綠地的可達性或可視性并不好：它們與香港不同，香港有著城市建成區嵌套于陡峭的大型公園之間的獨特布局。

郊野公園的面積通常較大。這意味著每位香港居民都靠近一處大型公園。這毫無疑問是個優勢。因此，公園的組成、分布和布局可能是造成擁擠的一項推動因素。如果我們將視點拉高，觀察珠三角地區的衛星視圖，香港和中山市的山地是珠江入?？跇酥拘缘拿娣e巨大的兩塊綠地。郊野公園不僅是香港的寶貴資源，也是整個珠三角地區的寶貴資源。

啟示3：地鐵線網的形態造成了擁擠

將TOD定義為圍繞高品質軌道系統創建緊湊、宜步、行人為主、功能混合的社區，本身會造成超高密度峰值。現在讓我們將目光移至港鐵線網系統的整體布局，其形態與擁擠有關嗎？

讓我們從一件趣聞開始說起。據一份有趣的報告指出，港鐵在設計時計劃每平方米車廂容納6位乘客，但最近乘客不愿意搭乘擁擠的地鐵，而愿意等候下一趟地鐵。由此導致運營中的地鐵每平方米車廂僅乘坐了4位乘客。有人指出，這可能是因為乘客需要多余的空間使用移動通訊設備。移動設備同樣改變了人們對交通出行的認識—出行途中的時間不再是靜寂的時間，而是富有成效的時間、應該是舒適的。這其實將簡單的效率問題復雜化，即出行速度越快，出行者的感受越佳。當你沉浸于移動設備之中，你會發現自己的目的地到的太快了……而你最終將和你的移動設備結伴，并根據旅程的長短做好計劃安排。

有多種方式可以減輕地鐵車廂內的擁擠，例如增加車廂數，增加人流密集站點的發車頻率，優化乘客位置分布等等。然而，車廂內擁擠雖得到緩解，但站廳內擁擠將會加劇。調價是減輕擁擠的另一種方式，但這與可持續交通使用的宗旨相違背。鼓勵錯峰出行是另一項策略。部分地鐵線路在非高峰時段提供免費或高折扣票價。倫敦市已嘗試多項獎勵措施，如注明在哪些站點之間步行快過搭乘地鐵，鼓勵市民選擇步行方式，以期減少地鐵擁擠現象。

盡管這些措施可提升地鐵系統的效率，但并未改變地鐵線路的布局，只能算是隔靴搔癢。網絡科學表明，地鐵線網布局的整體結構對線網各部分的使用量分布有著重大影響，進而會影響車廂和站廳內的擁擠情況。將香港與其他大多數城市的地鐵線路布局圖進行比較，不難發現香港的地鐵線網形態十分獨特。對于大部分城市的地鐵系統（圖03）而言，網絡的中間是一個相對較大的環形結構，將多個站點圍繞其中形成一個突出的核心。網絡的支線從這一環形結構向外輻射，延伸至城市的邊緣地區。支線長短不一，可分為短支和長支。對于港鐵（圖04）而言，支線是最突出的組成部分，線路距離長，延伸范圍遠。港鐵線網中的核心換乘站點并不多。相反，只有少數站點可稱作“核心站點”，包括：中環－香港站、金鐘站和尖沙咀－九龍站。然而，幾乎所有的支線均以平行的方式穿過旺角—旺角東—奧運區，在它們最終匯合到那幾個“核心站點”之前未發生任何交匯，以致該區成為高度擁堵和人群過度密集的垂直發展區。我們現在介紹第一個工具sDNA[3]，以便了解地鐵線網形態和擁擠之間的關系：模擬地鐵線網客流量。

圖05是網絡學模擬出的人流量潛力—線條越粗，表明客流量越大。網絡學的實證研究[5]已表明這些模擬與實際客流量密切相關，表明地鐵線網布局對客流量乃至車廂內和站廳內擁擠的影響。圖05顯示了巨量的地鐵客流在中環、九龍和港島東部的分布情況。從直觀上看，如果多條很長的軸向線路在同一個地區匯集，那么在匯集地區很可能形成擁擠。

香港地鐵的布局決定了支線之間的換乘必須經過網絡系統的中心區，這無疑增加了出行距離，并且為中心區帶來了不必要的客流量—環線和環狀放射線的網絡布局將會縮減經過中心區的多余行程，增加外圍線路可達性的同時縮短總體出行時間。

例如，新加坡規劃的地鐵延伸線，將采用主要環線搭配多個遠距離環線的結構，網絡中不存在孤立的盡端線路。盡管新加坡的地形不同于香港，但新加坡對于地鐵網絡布局的某些認識也許值得香港仔細研讀。巴黎的“大巴黎快線”項目目前也正在考慮轉變地鐵網絡的布局。

在香港，由于當前地鐵系統充足的乘坐量和成熟性，鮮有人提出大膽的城市規劃、交通規劃和城市設計方面的構想及其可能為香港帶來的變化?；蛟S深港兩地地鐵系統的對接，會帶來新的轉變；但由于未來對接的可能性較小，會帶來何種程度的轉變尚未可知。

“通過線網形態管理擁擠”作為戰略性的城市設計

回到地面，蜂擁于街道之中的綠色和紅色小巴以及大型雙層巴士在香港的城市出行中發揮著重要的作用。圖06與圖05相似，模擬港鐵、電車、輪渡和公交的客流量。觀察該圖，不難發現地鐵和公交線網的布局是如何引發人流集聚的。

盡管聚集有利于促進社會互動，形成城市優勢。正如我們此前所說，就香港而言，問題在于何種密度分布和布局會使聚集的缺點例如擁擠顯現。解決擁擠問題需要新的方法并進行相關研究。僅就上述討論而言，相關研究需要回答的問題包括：“地鐵和公交系統是否過于集中？”以及“地鐵和公交提供的可達性是否過于集中？”

從通過設立城市副中心，消除城市聚集產生的負面外部效應（擁堵、污染、擁擠和地價過高），改善經濟表現，將香港打造成多中心城市的角度來看，多數新市鎮未能實現合理的的職住平衡，令香港規劃界人士時常嘆息。建立新的城市副中心是一項解決之策，與之相關的另一項策略是城市副中心之間的相互連接，使之在功能上自成一體，獨立于主中心之外。這對香港作為服務型、知識型的經濟體或分散式、清潔型的制造業經濟體而言尤為重要。

何種地鐵線網布局有助于成功創建多中心城市？

TOD城市設計項目應當了解公交網絡流量中至關重要的軌跡分布和擁堵的風險。廣泛和持續的地鐵線路擴展應提前做好規劃。線路擴展不一定會改變各站點的可達性水平、客流量和發展潛力。盡管如此，對于正計劃通過修建新的地鐵系統帶來重大轉變的城市而言，上述前瞻性的發現對其城市設計具有重要的啟示。從城市設計旨在理解多尺度的空間分布、空間組成和空間布局所導致的結果來說，這是一種新型的城市設計。

理解公交可達性與就業區位的關系

分析工作地點的位置與公交可達性的關系，是著手解決該問題的一種方式。盡管并無有關香港工作地點位置分布的詳細數據—僅有區級數據且無更詳細空間層面的的替代數據可供使用—然而可用的信息顯示，港島、九龍、東九龍部分地區、葵芳和荃灣的“地鐵覆蓋區域”的工作地點占比達75%以上。鑒于該區公交可達性分布和建筑物分布情況，這很可能會加劇維多利亞港周邊狹小區域的過度集聚狀況。電信大數據證實了這一情況[7]。

工作地點過度集中并非香港獨有。倫敦、巴黎、紐約也面臨同樣的問題。公交網絡布局和就業區位之間的互動效應推動了兩者極度失衡的分布狀態，可能是造成香港和其他城市面臨這一問題的原因所在。香港的地鐵系統，盡管規模中等，但卻相對成熟；除非日后進行改變性的建設，否則目前計劃到2026年前完成的擴展項目（圖07）不會引發經過現有站點的流量軌跡發生大的變化。圖08顯示了環形線路對重新分布可達性和流量所起的作用。借助網絡科學的設計工具如sDNA完成的草圖規劃，可以對改造項目進行模擬，考察并開始思考如何更好地平衡地鐵網絡的可達性。

思考公交可達性與空間不公正的關系

由于地鐵線網布局是為了公共利益，在考慮設計地鐵網絡的形態時，同樣需要質問公交的可達性分布是否公正。由于40%的人口不居住在地鐵覆蓋區，而地鐵覆蓋區目前和將來都是增量最大的地區，因此我們需要思考如何才能公正地分配香港交通的可達性？即便我們同意地鐵線路建設通常以自上而下的方式完成，但這屬于城市政治經濟的一個重要方面，不應當僅靠港鐵公司一己之力。

總結及對城市設計師的建議

在非高峰時段，避開系統性擁擠區（圖05、06突出顯示部分），乘坐香港地鐵亦是一段愉悅的體驗。放眼世界，不論是在中國，還是倫敦、紐約、巴黎等大都市，都不可避免的存在地鐵系統擁擠的問題。這種擁擠不僅僅發生在地鐵車廂和地鐵站廳里，同樣發生于街道、公共空間和用作公共場所的室內空間 — 例如與地鐵站相伴的眾多商業空間 —“地鐵+物業”模式中的物業，拋開擁擠問題不談，這種模式是港鐵大獲成功的重要因素。

地理，“地鐵+物業”的盛行模式和復雜氣候狀況的組合，形成了香港似乎深不可測的復雜的空間分布、組成和布局形態。香港氣候具有三大鮮明特點：濕熱、臺風季節多強風和降雨、冬季氣候溫和。在這三大氣候特點、狹窄的地形、上世紀人車分流的交通設計理念的影響下，形成了多層次復雜交錯的地下、地面和空中步行系統。行人可從灣仔全程通過地下通道步行至中環，其間無需GPS的幫助，因為GPS無法確定你的位置。若在午餐時間和人流高峰時段選擇步行方式出行，則絲毫感受不到步行應有的暢通性和空間舒適性。

這些是城市設計未能提前作出有效應對的新狀況。多數城市設計理論主要關注增加城市活力，同時兼顧增加行人活動。而有關活力過旺的城市設計理論文獻和項目則少之又少。如何使有組織或漸進式的密度分散成為一種行之有效的城市設計策略？

新的狀況使得城市更新的興趣轉向并行結構城市和立體城市[2、6、9]。但，這是否就是解決問題的答案所在呢？或者，城市應該采用巴塞羅那那樣的超大街區布局[1]，通過預留更多的步行空間進行疏散？鑒于九龍和旺角有著與巴塞羅那相似的網格布局，它們是否應該使用象巴塞羅那那樣的超大網格結構？

暫且不提怎樣采取有效的干預和設計措施，城市設計師怎樣才能準確理解設計的復雜性？無疑可以先從繪圖著手。正如《懸浮城市》[6]一書所述，這些空間外形雖復雜但美觀，而美觀的外形會干擾城市設計師的設計決策，使其難以決定是作出改進、保持中立、小幅改動或與現狀大幅偏離？雖然交通規劃師持有精確的地鐵線路圖、公路網圖、公交線路圖、自行車路線圖和先進的建模技術，但在解決這一問題上，他們并不占優勢，他們手中并無步行網絡圖，并且對如何針對復雜的人行路徑建模并無良策。因此，香港大學已安排專門小組負責繪制香港室外（圖09&10）和室內（圖11）所有的人行通道。室內和室外包括地下、地面或空中。步行路線圖完成后，將成為可被計算機讀取的線性參考系統，當中標注線路的各項屬性特點。繪制步行路線圖旨在通過使用網絡科學的分析技術根據不同標準（圖12）模擬人流情況，了解香港的宜步性，人流擁擠發生的位置及采取干預措施的結果如何。該項目名為“宜步香港”，榮獲Walk21香港城市科技獎。宜步性是一個多維度指標，涉及重要的有形和無形維度。在香港，該指標會隨具體的天氣狀況，行人的個體情況、居住和工作生活軌跡、出行目的和動機而變化，同時受出行便利性和對促成出行而言屬重要的其他無形因素所影響。這對實現積極老齡化而言同樣重要。

《懸浮城市》一書涉及的復雜性和精彩描述并不能讓我們找到擺脫擁擠問題的潛在方法。有不少方式主張僅通過增加人行空間，減少感受到的人流量和實際擁擠情況。上文提到的巴塞羅那的超大網格結構便是其中一種。其他的潛在設計包括增加人行通道的密度，協調地面、地下或空中人行通道的關系。在將擁擠趕至他處之前，理解和預判這些“如果。。。就。。。”之類的設計干預措施如何被察覺、使用和有效緩解現有擁擠，是其中一個主要問題。這將是我們日后的工作。

The new crowdedness

Major cities in China are building and expanding metro systems as a strategy to improve sustainable mobility and reduce the negative environmental and social consequences of fast-paced motorization. In China, 33 cities have a metro network,and metro systems are currently under construction in 16 additional cities with many more under planning and being proposed. As the number of passengers choosing the metro for daily transportation increases, crowdedness, previously a problem on metro trains, are now common in many metro stations and in the approach to the stations.

This relatively new crowdedness phenomenon is not unique to China; it is experienced in New York, London, Paris and many other cities. These are new urban conditions that urban design is not very well prepared to deal with. Most of urban design theory is predicated on increasing vitality, associated with increasing pedestrian activity. Not much is to be found in the urban design literature and projects about the opposite phenomenon: too much vitality. Yet, since crowding is both perceptual and objective, urban design can play an important role in understanding how to con fi gure progressive and diversi fi ed level of urban buzz.

How can organised or progressive dispersion be a meaningful urban design strategy?

By this, we do not mean crowd management–the management of people movement and behaviour during major events, which has its own specialised techniques and literature. Events may induce limited crowdedness in place and time while place crowding is more or less continuous. Crowding is what causes people to start to avoid an area because it is perceived as having too much people intensity and vitality. Designing for progressive vitality is to allow vitality to grow and expand and still offer a range of vitality levels. Designing for progressive vitality entail understanding when an area is stressed by over intensity and vitality and why.

Learning from Hong Kong?

Hong Kong is a city of extreme con fi gurations, which are a unique mix of extreme geography, climate, institutions, development history, and urban innovation.Combining steep geography and water, only 20% of Hong Kong’s territory has a slope of less than 1 to 5. On this has been built a hyper-dense city with an extremely successful Transit Oriented Development (TOD) system, making it an extraordinary and dazzling urban landscape between water, green ‘wall’ hills, hyper density, MTR and road infrastructure.

Hong Kong is one of the most comprehensive TOD cities in the world. It has always received “best of” accolades for its public transport. It is endlessly repeated that public transport accounts for 90% of commuting, a sort of unreachable platinum sustainable transport standard. Yet Hong Kong is a crowded city, with high level of crowdedness within its metro (MTR) carriages, MTR stations and in the complex surroundings of the stations. At certain times, this crowdedness can also be found in many streets. What can we learn from Hong Kong about crowdedness, urban form and urban design?

Does it mean that Hong Kong can be a model to learn from? How does an understanding of how hyper-crowdedness is generated help us design its mitigation?The oft-repeated phrase that “in Hong Kong land is scarce” needs to be quali fi ed:“in Hong Kong fl at and easily buildable land is very scarce”. So, for the Hong Kong model to make sense, one may fi rst have to build some hills, since most large cities are mostly fl at, and Hong Kong’s spatial solutions would make little sense.

Nevertheless, we can gain insight into the phenomenon of crowdedness, and its relationship to shape from analysing different aspects of how Hong Kong has responded to its spatial constraints, and draw insights into how to manage crowdedness. In this paper we aim to sketch out the characterisation of the extreme configurations of Hong Kong, proposing that if we understand the relationship between these extreme configurations and crowdedness we might be able to understand how to design “diversi fi ed” or “progressive level of” crowdedness. This might lead to an approach of city crowdedness mitigation that could be transferable.The rest of this paper discusses some lessons drawn from reflections on and analysis of the relationship between crowdedness and urban con fi guration in Hong Kong, at various scales. Tools and techniques for analysing this relationship are also discussed.

lnsight 1: Compactness is not a requirement for crowdedness

To explore the question of whether compactness is needed to generate crowdedness, we start by looking at Hong Kong’s overall urban form, including the MTR and bus network and green space composition, distribution and con fi guration before zooming in, asking how this may contribute to crowdedness.

In the urban form debate, the question of compact versus sprawl is prominent, as if these were direct opposites of each other. Let us explore this question by asking,“Is Hong Kong compact?” The answer, at the territory scale, is no. Hong Kong is a vertical city with low consumption of land per capita, it is an extremely dense city,yet it does not make it automatically compact. But neither is Hong Kong classically sprawling. Although there is no agreed de fi nition of sprawl, at least three features usually characterise it: low density, scattered, and discontinuous distribution, and association with car dependant transport.

Compactness means close and bounded as opposed to scattered and discontinuous. We intuitively perceive a circle or a square as compact. If we want to give it a quantitative characterisation we could use a shape index used in landscape studies. A circle would have a compactness of 1; the square will be 1.27 in terms of shape index (Fig. 01). Scrutinising the urban form of Hong Kong, one notices ribbon developments linked by the MTR and very engineered road infrastructure.The shape index of Hong Kong is 83, which is far from a compact urban form (Fig.02). Hong Kong’s urban form does not have much of a compact shape except for the very limited Kowloon area. Overall Hong Kong’s urban morphology is an assemblage of separated ribbons framed by steep hills, or between hills and water.Hong Kong density profile, its density transect (resident + work place) from the centre outward, is unlike most cities which are denser at their centre and have a more or less gentle decreasing slope outward. For Hong Kong, density goes from extremely high to “nothing” and then to very high again, then “nothing” whether it is water or country park. Hong Kong density is critically spiky, but the number of spikes is much reduced.

What Hong Kong shows us is that compactness of the overall urban shape in the sense of ‘urbanisation continuity’, is not a pre-requisite of crowdedness. In fact,compactness of shape may actually mitigate crowdedness.

lnsight 2: Large park con fi guration is a possible driver of crowdedness

If Hong Kong is not compact, what happens between all the high-density ribbon linked by the MTR and roads? In between are Hong Kong’s Hilly Woodland, shrub and grass land, which occupy almost 65% of the territory. This is a hyper-dense city in hilly park settings. In most cities, these areas will be fl at land and mostly builtup area interspersed with green spaces and parks. Hong Kong is the reverse. Most cities boasting a lot of park/green space do not mention that these green spaces are mostly at the periphery of the build-up area. These green spaces are not very accessible or visible from the densest part of the city: unlike Hong Kong which has a privileged con fi guration of steep large parks with built-up area nested between them.

The Country Parks are usually large. It means that anyone in Hong Kong is near a very large Park. This is certainly an advantage. So, the composition, distribution and con fi guration of parks are possibly a driver of crowdedness. If we zoom out to the Pearl River Delta (PRD) satellite view, Hong Kong and Zhongshan hills are the giant green areas that mark the Pearl River mouth. The Country Parks are not just precious and valuable to Hong Kong, but also precious to the whole PRD.

Insight 3: Metro network shape underlies crowdedness

The de fi nition of TOD as creation of compact, walkable, pedestrian-oriented, mixeduse communities centred around high quality train systems lends itself to hyper density spikiness. Let us now turn to examining the overall layout of the MTR system. Does the MTR network shape matter for crowdedness?

Let us start with an anecdote. There is an intriguing report that the MTR was designed for 6 people per square meter yet recently people are less willing to board a crowded train and wait to the next one–which lead to train operating at 4 people per square meter only. It has been suggested that this might be due to the space needed to use mobile device. Mobile devices have also changed the meaning of transport journey–it is no more a dead time, it is a productive time that should be comfortable. It complicates the simplistic eきciency story that the faster the transport journey is, the better it is. If you are in the middle of something on your mobile device, you may fi nd that your destination has arrived too soon… You also end up having activity with your mobile devices that are linked to the expected length of the journey.

There are many ways of reducing in-carriage crowding in metros such as making train longer by adding carriage, increasing service frequency on busy sections of the network, distributing better the passenger along the train, and so on. However,in-carriage crowding can be reduced but in-station crowdedness will increase.Pricing is another way to reduce crowding, yet it would be contrary to the objectives of sustainable transport usage. Smoothing the peak time, is yet another strategy.Some metros oあer free or heavily discounted pricing when travelling outside peak hours. London has resorted to various enticements for people to walk more in an attempt at reducing metro crowding by indicating the travel time between stations where walking between stations is faster than taking the metro.

While these measures can be seen as making the system more eきcient, they are‘tinkering at the margin’; they do not change the layout of the network. Network science shows that MTR network layout overall structure has a large impact on usage distribution over parts of the network and as such on crowdedness in-carriage and in-stations. The Hong Kong MTR network shape is unique if we compare a diagram of most metro system lines layout with HK MTR line layout diagram. For most metro systems (Fig. 03), a relatively large ring encircles a prominent core of stations. Branches radiate from the core and reach further areas of the urban system. The branches have diあerent size and can divide in short and longer spur.For Hong Kong (Fig. 04), the branches are the most prominent components. The branches are very long and extend far away. There is not really a signi fi cant number of interlinked cores of stations. Instead, there are only a very small number of core stations, to the extent that these form a ‘point’ comprising just three stations:Central-Hong Kong Station, Admiralty and Tsim Sha Tsui-Kowloon. However, almost all these branches pass through the Mong Kok–Mong Kok East–Olympic area,where they run parallel but do not meet before ultimately ending up in the ‘point’,making this as a very congested and over-crowded vertical extended area.

We now introduce the first tool, sDNA [3] for providing insight into the shapecrowdedness relationship: modelling network fl ows.

Fig. 05 is a network science simulation that shows fl ow potential–the thicker the line the higher the fl ow. Empirical network science studies [5] have shown that these simulations are well-related to actual fl ow, showing the impact of the metro layout on flow and consequently to in-carriage and in-station crowding. Fig. 05 shows how Central, Kowloon and the eastern part of Hong Kong Island are well-served by massive fl ow. Intuitively, this makes sense: if there are very long radials ending up in the same place it is likely to be crowded in the converging area.

The HK MTR layout obliges journey between branches to always go through the centre, making journeys longer and unnecessarily adding the number of passengers going through the centre–circle line and looped radial lines would remove these extraneous journeys through the centre and contribute in shifting accessibility outward but also reducing overall journey time for all.

The planned Singapore metro extensions, for example, will have a major circle line and many more long-range loops resulting in no dead-end line. While Singapore’s geography is different, still there is something they seem to know about metro system layout that Hong Kong may want to scrutinise. Paris with the Grand Paris Express project, is currently also making a transformational change to the metro layout.

In HK, it seems that very little daring conceptual urban planning, transport planning and urban design thought has been given to how this may change given the current critical mass and maturity of the MTR system. Perhaps the connection of Shenzhen metro system with Hong Kong MTR will change these relationships, although to what extent is unknown given that the future connectivity potential is rather minimal.

‘Managing crowdedness by network shape’ as strategic urban design

Coming back to the ground and returning to what plays an important role in moving Hong Kong, are the swarms of small green and red buses and large double decker zipping around all Hong Kong roads. Fig. 06 shows a similar simulation than Figure 05, this time for the HK metro, tramways, ferries and the buses. One can see how the MTR and the bus network con fi gurations induce very concentrated fl ows.

While the bene fi t of agglomeration is what makes the advantage of city, enabling high potential for interactions; as we have already argued, in the case of Hong Kong, the question needs to be reversed as to what configuration of density distribution and composition create agglomeration dis-bene fi t such as crowdedness.A new approach to crowdedness and accompanying research are needed.Following on from the discussion above, the accompanying research will need to answer questions such as, “Is the metro and bus system over centralised?” and “Are accessibility provided by metro and bus over centralised?”

In the perspective of creating a more polycentric Hong Kong, by creating subcentres that will improve economic performance by diminishing the negative externalities of agglomeration (congestion, pollution, crowdedness, and high land prices), planners in Hong Kong always lament of the failure at creating more balanced work place resident ratio in most of the new towns. One strategy is new sub-centres creation; another accompanying one is to inter-link these subcentres in such a way that they can function as a system that is much more independent of the major centre. This is more so in a service, knowledge economy or distributed clean manufacturing economy.

What sort of metro network con fi gurations would support the successful creation of a polycentric city?

Any TOD urban design project should understand the strategic trajectories of public transport network flow and crowdedness risks. Extensive and successive MTR extensions are planned well in advance. They may or may not alter much the accessibility ranking of each station, fl ow potential and thus their development potential. Nevertheless, such forward-looking fi ndings are important to inform urban design in cities that are undergoing massive transformation via new metro system.This is new urban design in the sense that urban design aims to understand the outcomes of multi-scale relation of spatial distribution, spatial composition, and spatial con fi gurations.

Understanding public transport accessibility’s relation to work place location

One way of beginning to address this question would be to analyse public transport accessibility in relation to work place location. While there are no detailed data of work place locations in Hong Kong - the information is at district level and there is no easy alternative to use as proxy at more detailed spatial level - the information available indicates that the “metro area” which comprises Hong Kong Island,Kowloon, part of Kowloon East, Kwai Fong and Tsuen Wan have more than 75% of work places. Given the distribution of the public transport accessibility and the built distribution in that area, it is likely that this is further over-concentrated in a very small area around Victoria harbour. Big data phone traces con fi rm it [7].

Over-concentration of workplace is not unique to Hong Kong. London, Paris, and New York have a similar pattern. In Hong Kong as elsewhere this might be due to the very unbalanced distribution that is fuelled by the interaction of the public transport network configuration and work place location. The Hong Kong metro system, despite its middle size, has become a very mature system, and unless transformational project occurs, the future extension currently projected by 2026 (Fig.07) will not alter much the trajectory of the existing metro station for good or bad. In Fig. 08, one can see the eあect of how looped lines start to re-distribute accessibility and flow. Sketch-planning via network science design tools such as sDNA allow insight by simulating such transformational projects and start thinking how MTR accessibility could be better balanced.

Considering public transport accessibility’s relationship to spatial inequity

In considering the design of the metro network shape, the equitability of distribution of public transport accessibility is also to be questioned, given that the metro layout is meant to be a public good. Given that 40% of the population do not live in the metro area, and this is the area that has and will have the largest growth, how equitable is the distribution of accessibility in Hong Kong? This is an important aspect of urban political economy that can’t just be left to the MTRC even if we agree that metro line building is usually a top down process.

Conclusions and recommendations for urban designers

Experiencing the Hong Kong MTR is extraordinary as long that one stays within the system and avoids peak time. The systematic crowding areas are highlighted in Fig. 05 and 06. Metro crowding is also found in many metro systems in the world whether in China or in large metropolis like London, New York, Paris, etc. Not only crowding is occurring in metro carriages and stations; but also in streets, public spaces and indoor spaces that work as public spaces–for example the many commercial spaces that are associated with MTR stations–the properties that are part of the “rail+property” model and beyond that makes the success of the MTR.

The combination of geography, and the proliferation of MTR “rail+property” formula and Hong Kong climate complex regimes lead to a spatial distribution, composition and configuration complexity that seems unfathomable. The Hong Kong climate has three distinctive regimes, very hot and humid, windy and rainy, typhoon season and agreeably temperate weather in winter. Designing for these three regimes in a tight geography combined with late 20th century traffic ideology of pedestrian segregation has resulted in the multi-level complex entanglement of below, at grade and above ground pedestrian realms. You might walk from Wan Chai to Central,where GPS might not be of help as GPS does not even know where you might be,without setting foot on the ground. Lunch time and certainly peak time walking might verge on nothing near a de fi nition of walkability as moving in an unimpeded manner with much space.

These are new urban conditions that urban design is not very well prepared to deal with. Most of urban design is predicated on increasing vitality, associated with pedestrian activities–not much is to be found in the urban design theory literature and projects about the issue of too much vitality. How organised or progressive density-dispersion can be a meaningful urban design strategy?

These new urban conditions have generated a renewal interest for the parallel cities and the multi-level cities [2, 6, 9]. Yet is it the answer? Or should it be the super blocks like in Barcelona [1], to give much more space to pedestrian–dispersion by allocating more space to pedestrian? Should the Barcelona super-grid be implemented in Kowloon and Mong-Kok given their grid like Barcelona layout?

How does an urban designer start to comprehend such a complexity let alone intervene and design meaningfully? Mapping is certainly a start. As the book Cities without Ground [6] demonstrates so well, these spaces are tantalising yet in their appearance of capturing complexity, the beautiful drawing deceive as to what any intervention might do? Improve, be neutral, marginal change or major departure from the current situation. Transport planners are not better placed while they have very accurate map of the metro network, the road network, the bus network, the cycling network and rather sophisticated modelling techniques, they do not have a map of the pedestrian network and are rather puzzled on how to model the complexity of the pedestrian journey. Therefore a team at HKU [11] has started to do the mapping for all the pedestrian paths of Hong Kong outdoor (Fig. 09 & 10) and indoor (Fig.11). Indoor and outdoor might be below ground, at grade or above ground. Once this map is completed, it becomes a machine readable linear referencing system to which qualities of the journey can be attached. The aim is to use network science and simulate pedestrian fl ow according to various criteria (Fig. 12) to understand how walkable is Hong Kong, where are the crowding areas and what if interventions might change them. The project is called WalkableHK. WalkableHK received the Walk21 Hong Kong CityTech Awards. Walkability is multi-dimensional with important tangible and intangible dimensions. In Hong Kong, it changes according to climate regime of the day and time, individual profile, residential and work life trajectories, purposes and motivations, mixing both convenience and more intangible characteristics that are nevertheless important to incentivise walking. This is certainly also important for active aging.

The complexity involved and beautiful depictions in Cities without Ground do not allow us to assert potential way out of crowdedness. There are many ways to reduce pedestrian perceived and actual crowdedness by simply increasing space for pedestrian. Barcelona’s super-grid mentioned above is such an example.Other potential design exists such as increasing the density of pedestrian ways,coordinate parallel at grade, below or above ground pedestrian ways. One of the key issues is to understand and anticipate how these “what if” design interventions are perceived and lived and how they successfully reduce the existing crowdedness without displacing it. This is our future work.

[1] Barcelona superblock http://ajuntament.barcelona.cat/ecologiaurbana/en/what-we-do-and-why/quality-public-space/superblocks

[2] Blauvelt, A., Yoos, J. & James, V., 2016. Parallel Cities: The Multilevel Metropolis. Minneapolis: Walker Art Center.

[3] Chiaradia, A., Cooper, C., Webster, C. (2010) sDNA, spatial Design Network Analysis, Cardiff University, Hong Kong University

[4] Curtis, C. and Scheurer, J., 2016. Planning for public transport accessibility: an international sourcebook. London: Routledge.

[5] Derrible, S. and Kennedy, C., 2011. Applications of graph theory and network science to transit network design. Transport reviews, 31(4), pp.495-519.

[6] Frampton, A., Wong, C. and Solomon, J., 2012. Cities without ground: a Hong Kong guidebook. Oro editions.

[7] Grauwin, S., Sobolevsky, S., Moritz, S., Gódor, I. and Ratti, C., 2015. Towards a comparative science of cities: Using mobile traffic records in New York, London, and Hong Kong. In Computational approaches for urban environments (pp. 363-387). Springer International Publishing.

[8] Kanga C, Mab X., Tongc T, Liu Y. 2012, Intra-urban human mobility patterns: An urban morphology perspective, Physica A 391 (2012) 1702—1717

[9] Mangin, D., Girodo, M., Eds, (2016) Mangroves urbaines: du métro à la ville (Paris, Montréal,Singapour), Paris: La Découverte, collection Dominique Carré.

[10] Roth, C., Kang, S.M., Batty, M. and Barthelemy, M., 2012. A long-time limit for world subway networks. Journal of The Royal Society Interface.

[11] WalkableHK, (2016) Guibo, S., Zhang, L., Sarkar, C., Zhang, X., Webster, C., Chiaradia, AJF., The University of Hong Kong, Faculty of Architecture

[12] Zhang, L., Chiaradia, A. and Zhuang, Y., 2015. A Configurational Accessibility Study of Road and Metro Network in Shanghai, China. In Recent Developments in Chinese Urban Planning (pp. 219-245).Springer International Publishing.