刊首语

刊首语

割裂与缝合

北京林业大学与清华大学之间仅隔着一条铁路，这就是京张铁路。20世纪80年代时学校的周边还是农田和村庄。那时京张铁路上火车很少，我们步行或骑车去一趟清华没什么不便，但是封闭的铁路线所形成的物理隔离，还是在无形之中拉大了两个学校之间的距离。

后来快速的城市化迅速波及学校的周边，曾经的城市边缘地带突然成为城市的繁华地区，不断扩展的城市将京张铁路包围起来。与此同时，小汽车开始进入了千家万户，自驾车成为市民交通出行的主要选择之一。经济的发展使得人流和物流剧增，京张铁路也繁忙起来，于是铁路与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为拥堵的地段，每当我要去相邻的清华大学，想到恶劣的交通环境，便会有不小的心理压力。

不仅仅是铁路，当代城市中修筑的大量宽阔的封闭或半封闭的机动车快速路也会对城市环境和社会生活造成阻隔。随着汽车工业的发展和私人轿车的普及，汽车主导了中国城市的发展，北京就是一个典型。我们学校南面的四环路，北面的五环路，东面的京藏高速公路都是近20年来陆续建成的，而西边正在建设四环路通往京新高速公路的通道。这些快速路试图在城市不同区域之间建立起快速的联系，但是由于路宽、封闭和过街设施缺乏等原因，道路两侧的联系却极其困难，近在咫尺的目的地都难以到达。

城市交通是一个非常综合和复杂的问题。现代化的城市需要现代化的交通基础设施，但问题是，许多交通基础设施的建设是以增加机动车的通行量为导向，在提高机动车通行效率的同时，却造成了非机动交通环境的严重恶化，以步行和自行车为代表的“低效”慢行通行方式逐渐被忽视和淘汰。这就形成了一个可怕的怪圈：车越多，越需要修路；路越宽，越需要开车；开车越多，路就越拥堵，于是需要更宽的路。不仅是城市快速路宽阔得可以称得上“壮观”，6车道或8车道的城市道路也屡见不鲜，而非机动车道和人行道却被不断缩减。这种趋势不仅在大城市中蔓延，甚至开始影响中小城市。

现代城市中被用来满足交通需求的空间数量非常惊人。交通空间的无限制扩张不仅带来城市的割裂，而且造成大量土地资源的浪费。但问题的另一面往往也是机遇，随着中国未来城市化由粗放型扩张向精细化更新的方向发展，这些空间都能被看作是建成区可以被利用的重要空间资源，通过创造性的设计，就能够实现多种公共功能与交通服务功能在同一个城市空间的共生。未来的城市将有可能在机动交通网络之上，叠加一个可以承载慢行交通等多种功能的景观系统。

60年前，梁思成先生曾设想保留北京的老城墙并建造环城公园。今天，城墙已经消失，取而代之的是分割北京老城内外的二环路。但如果我们有创造一个更好城市的决心，并以新的思路来看待城市交通基础设施，未来环城公园就有可能实现——它将位于今天的二环路之上，重新缝合老城内外的空间。护城河也可以恢复，并成为抵御雨洪威胁的城市水系的重要组成部分。这样一个环城公园将成为市民出行、游憩和运动的公共空间，也将是北京重要的生态廊道。再大胆设想一下，如果北京的环路都整体或部分地成为地下和半地下设施，上面是环绕城市的绿环和开放空间，那么这个城市与我们今天看到的北京城将会完全不同。

再回过头看我身边的京张铁路。北京成功申办冬奥会后，京张铁路升级改造并在城区段采用地下线的方式也逐渐明确。随着铁路的停运和改造工程的展开，我们学校与清华大学之间的道路拥堵情况有所缓解。然而我更关心的是这条废弃的地面铁路线未来的命运。随着铁路下地，我看到了一条从城市北郊向南，连接五环、四环和三环，并一直延伸到二环路西直门的潜在的绿色廊道，看到了长期隔离的铁路线两侧的城市重新被连接和缝合在一起的可能。如果真的能够实现这条绿色廊道，它将提供一条9km长的环境优美的城市慢行系统，极大地鼓励绿色交通方式；它将创造人性化的城市环境，提供更多的公共空间和休闲娱乐功能；它可以带来周边地区更多的商业机会，促进周围社区的活力；它可以成为一条生态廊道，为生物提供栖息场所，增加城市中的生物多样性；当然，它也能够加强周边不同人群的交往和融合，包括促进两侧诸多高校师生的交流和往来。

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