刊首語(yǔ)

割裂與縫合

北京林業(yè)大學(xué)與清華大學(xué)之間僅隔著一條鐵路，這就是京張鐵路。20世紀(jì)80年代時(shí)學(xué)校的周邊還是農(nóng)田和村莊。那時(shí)京張鐵路上火車很少，我們步行或騎車去一趟清華沒什么不便，但是封閉的鐵路線所形成的物理隔離，還是在無(wú)形之中拉大了兩個(gè)學(xué)校之間的距離。

后來(lái)快速的城市化迅速波及學(xué)校的周邊，曾經(jīng)的城市邊緣地帶突然成為城市的繁華地區(qū)，不斷擴(kuò)展的城市將京張鐵路包圍起來(lái)。與此同時(shí)，小汽車開始進(jìn)入了千家萬(wàn)戶，自駕車成為市民交通出行的主要選擇之一。經(jīng)濟(jì)的發(fā)展使得人流和物流劇增，京張鐵路也繁忙起來(lái)，于是鐵路與道路平交形成的四道口、五道口和六道口等路口成了北京市最為擁堵的地段，每當(dāng)我要去相鄰的清華大學(xué)，想到惡劣的交通環(huán)境，便會(huì)有不小的心理壓力。

不僅僅是鐵路，當(dāng)代城市中修筑的大量寬闊的封閉或半封閉的機(jī)動(dòng)車快速路也會(huì)對(duì)城市環(huán)境和社會(huì)生活造成阻隔。隨著汽車工業(yè)的發(fā)展和私人轎車的普及，汽車主導(dǎo)了中國(guó)城市的發(fā)展，北京就是一個(gè)典型。我們學(xué)校南面的四環(huán)路，北面的五環(huán)路，東面的京藏高速公路都是近20年來(lái)陸續(xù)建成的，而西邊正在建設(shè)四環(huán)路通往京新高速公路的通道。這些快速路試圖在城市不同區(qū)域之間建立起快速的聯(lián)系，但是由于路寬、封閉和過街設(shè)施缺乏等原因，道路兩側(cè)的聯(lián)系卻極其困難，近在咫尺的目的地都難以到達(dá)。

城市交通是一個(gè)非常綜合和復(fù)雜的問題?，F(xiàn)代化的城市需要現(xiàn)代化的交通基礎(chǔ)設(shè)施，但問題是，許多交通基礎(chǔ)設(shè)施的建設(shè)是以增加機(jī)動(dòng)車的通行量為導(dǎo)向，在提高機(jī)動(dòng)車通行效率的同時(shí)，卻造成了非機(jī)動(dòng)交通環(huán)境的嚴(yán)重惡化，以步行和自行車為代表的“低效”慢行通行方式逐漸被忽視和淘汰。這就形成了一個(gè)可怕的怪圈：車越多，越需要修路；路越寬，越需要開車；開車越多，路就越擁堵，于是需要更寬的路。不僅是城市快速路寬闊得可以稱得上“壯觀”，6車道或8車道的城市道路也屢見不鮮，而非機(jī)動(dòng)車道和人行道卻被不斷縮減。這種趨勢(shì)不僅在大城市中蔓延，甚至開始影響中小城市。

現(xiàn)代城市中被用來(lái)滿足交通需求的空間數(shù)量非常驚人。交通空間的無(wú)限制擴(kuò)張不僅帶來(lái)城市的割裂，而且造成大量土地資源的浪費(fèi)。但問題的另一面往往也是機(jī)遇，隨著中國(guó)未來(lái)城市化由粗放型擴(kuò)張向精細(xì)化更新的方向發(fā)展，這些空間都能被看作是建成區(qū)可以被利用的重要空間資源，通過創(chuàng)造性的設(shè)計(jì)，就能夠?qū)崿F(xiàn)多種公共功能與交通服務(wù)功能在同一個(gè)城市空間的共生。未來(lái)的城市將有可能在機(jī)動(dòng)交通網(wǎng)絡(luò)之上，疊加一個(gè)可以承載慢行交通等多種功能的景觀系統(tǒng)。

60年前，梁思成先生曾設(shè)想保留北京的老城墻并建造環(huán)城公園。今天，城墻已經(jīng)消失，取而代之的是分割北京老城內(nèi)外的二環(huán)路。但如果我們有創(chuàng)造一個(gè)更好城市的決心，并以新的思路來(lái)看待城市交通基礎(chǔ)設(shè)施，未來(lái)環(huán)城公園就有可能實(shí)現(xiàn)——它將位于今天的二環(huán)路之上，重新縫合老城內(nèi)外的空間。護(hù)城河也可以恢復(fù)，并成為抵御雨洪威脅的城市水系的重要組成部分。這樣一個(gè)環(huán)城公園將成為市民出行、游憩和運(yùn)動(dòng)的公共空間，也將是北京重要的生態(tài)廊道。再大膽設(shè)想一下，如果北京的環(huán)路都整體或部分地成為地下和半地下設(shè)施，上面是環(huán)繞城市的綠環(huán)和開放空間，那么這個(gè)城市與我們今天看到的北京城將會(huì)完全不同。

再回過頭看我身邊的京張鐵路。北京成功申辦冬奧會(huì)后，京張鐵路升級(jí)改造并在城區(qū)段采用地下線的方式也逐漸明確。隨著鐵路的停運(yùn)和改造工程的展開，我們學(xué)校與清華大學(xué)之間的道路擁堵情況有所緩解。然而我更關(guān)心的是這條廢棄的地面鐵路線未來(lái)的命運(yùn)。隨著鐵路下地，我看到了一條從城市北郊向南，連接五環(huán)、四環(huán)和三環(huán)，并一直延伸到二環(huán)路西直門的潛在的綠色廊道，看到了長(zhǎng)期隔離的鐵路線兩側(cè)的城市重新被連接和縫合在一起的可能。如果真的能夠?qū)崿F(xiàn)這條綠色廊道，它將提供一條9km長(zhǎng)的環(huán)境優(yōu)美的城市慢行系統(tǒng)，極大地鼓勵(lì)綠色交通方式；它將創(chuàng)造人性化的城市環(huán)境，提供更多的公共空間和休閑娛樂功能；它可以帶來(lái)周邊地區(qū)更多的商業(yè)機(jī)會(huì)，促進(jìn)周圍社區(qū)的活力；它可以成為一條生態(tài)廊道，為生物提供棲息場(chǎng)所，增加城市中的生物多樣性；當(dāng)然，它也能夠加強(qiáng)周邊不同人群的交往和融合，包括促進(jìn)兩側(cè)諸多高校師生的交流和往來(lái)。

Separation and Reconnection

A passing through railway is the only partition between Beijing Forestry University and Tsinghua University, which is the Beijing-Zhangjiakou Railway. The campuses were surrounded by farmland and villages in the 1980s. Very few trains was running through the railway then, so it was convenient for us to walk or bike to Tsinghua University, but the continuous railway line still formed physical separation, widening the distance between the two campuses.

Later, rapid urbanization quickly spread to the periphery of the campuses, and the once urban fringe suddenly became busy area, and the sprawling urban area encircled the railway. At the same time, cars began to be owned by thousands of families and driving turned to be one of the main choices for citizens’ commuting. Economic development brought about the soar of population and goods flow, the Beijing-Zhangjiakou Railway became busier, so the grade road crossings of Sidaokou, Wudaokou and Liudaokou became the most congested areas in Beijing. I would be in such a stress whenever I wanted to go to the adjacent Tsinghua University and thought of the poor traf fi c condition.

Not only the railway, but the huge and closed or semi-closed expressways built in cities can also be obstructs in urban environment and social life. With the development of the automobile industry and the popularity of private cars, motor vehicles have dominated the development of cities, and Beijing is a typical example. The Fourth Ring Road at the south of our campus, the Fifth Ring Road at the north and the Beijing-Tibet Expressway of the east were successively built in the past 20 years, and the highway connecting the Fourth Ring Road and Beijing-Xinjiang Expressway is in construction on the west. These expressways are trying to develop rapid linkage between different areas, but due to the considerable road width, closed accessibility and the lack of crossing facilities, the traversing between two sides is extremely dif fi cult, people can hardly reach it even the destination is near at hand.

Urban transportation is a very comprehensive and complex issue. Modern cities need modern transportation infrastructure, but the problem is that many of the transportation infrastructure construction is to increase the traffic of motor vehicles, so that caused serious deterioration of non-motor vehicle traffic environment when improving the efficiency of motor vehicles, quot;inefficientquot; slow-traffic represented by walking and cycling are gradually neglected and eliminated. This creates a terrible cycle∶the more cars, the more need to build roads; the wider the roads, the more people need to drive; the more people drive, the more congestion city would get, and then the city needs wider road. Not only are the city's expressways wide enough to be described as quot;spectacularquot;, but the six or eight-lane urban roads are also common, while the non-motorized lanes and sidewalks are being continuously narrowed down. This trend is spreading not only in metropolis, but even in smaller cities.

The area of spaces that are used to meet traffic needs is staggering in modern cities. The unlimited expansion of transportation space brings about not only the division of cities, but also the huge waste of land resources. But the opportunities often occur on the other side of the problems. As China's future urbanization would go toward elaborate renovation from extensive expansion, these spaces can be regarded as important resources for further reuse, and may achieve the symbiosis of a variety of public functions and services in a certain piece of urban space through creative design. The future city will likely to be able to superimpose a landscape system that can carry a variety of functions such as slow-traf fi c above the motor vehicle transportation system.

Mr. Liang Sicheng once conceived of the preservation of the old city walls and the construction of the surrounding city park sixty years ago. Yet today, the walls have been removed and replaced by the Second Ring Road, which separates the inside and outside of the old Beijing City. But if we have the determination to create a better city, and consider the urban transportation infrastructure in a new perspective, the futurering park is worth expecting— it will be located on the Second Ring Road, reconnecting the inside and outside spaces of the old city. The city moat may also be restored and become an important component of the urban water system which can resist rain- fl ood threats. Such a ring city park will be a public space for citizens’ shuttling, recreation and exercise, and will also be an important ecological corridor in Beijing. Bold to imagine, if the ring roads in Beijing are wholly or partly underground or semi-underground, above which is the green ring and open space loop rounding the city, it would be completely different from the city we see today.

Looking back at the Beijing-Zhangjiakou Railway. After Beijing's successful bid for the Winter Olympics, the upgrading plan of the Beijing-Zhangjiakou Railway which buries partly underground lines in urban areas is gradually clear. The road congestion between our university and Tsinghua University has eased with the suspension and renovation of the railway. However, I am more concerned about the future fate of this abandoned ground railway. With the railway buried underground, I see a potential city green corridor from north to south, connecting the Fifth, Forth and Third Ring Road, and extending to the Xizhimen at the Second Ring Road, and see the possibility of reconnecting the long isolated areas of the city. If this green corridor can be realized, it will provide a ninekilometer-long beautiful urban slow-traf fi c system that encourages green transportation. It will create a humanized urban environment and provide more public spaces and recreational functions. It can bring more business opportunities for the surrounding area and stimulate the vitality of surrounding communities. It can be an ecological corridor to provide habitats for creatures and increase biodiversity in the city. Of course, it can also strengthen the exchange and contact of various groups of people, including promoting the communication between teachers and students of the universities on both sides.

Translator∶ WANG Xi-yue

Chief Editor∶ Prof. WANG Xiang-rong

October 10th, 2017