Trees and the Public Realm - Westminster City Council
Trees and the Public Realm - Westminster City Council
Trees and the Public Realm - Westminster City Council
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Appendix C - 2<br />
<strong>Trees</strong> <strong>and</strong> <strong>the</strong> <strong>Public</strong> <strong>Realm</strong> (Draft)<br />
These required minimums are very useful when planning <strong>the</strong> development of large sites, with new streets, but<br />
<strong>Westminster</strong> has few areas where such development is likely to occur in <strong>the</strong> short or medium term. Many of<br />
our existing streets were not designed to modern st<strong>and</strong>ards, <strong>and</strong> <strong>the</strong>re is simply insufficient width to provide a<br />
minimum of 2m clear for pedestrians. Never<strong>the</strong>less, this is our aim, balanced against <strong>the</strong> benefits of<br />
providing street trees, in order to avoid not only inconvenience, but danger that can occur by encouraging<br />
stepping into <strong>the</strong> carriageway.<br />
Where this is not practical, we revert to The DfT’s Inclusive Mobility, which states:<br />
“A clear width of 2m allows two wheelchairs to pass one ano<strong>the</strong>r comfortably. This should be regarded<br />
as <strong>the</strong> minimum under normal circumstances. Where this is not possible because of physical<br />
constraints 1.5m could be regarded as <strong>the</strong> minimum acceptable under most circumstances, giving<br />
sufficient space for a wheelchair user <strong>and</strong> a walker to pass one ano<strong>the</strong>r. The absolute minimum, where<br />
<strong>the</strong>re is an obstacle, should be 1m clear space. The maximum length of restricted width should be 6<br />
metres. If <strong>the</strong>re are local restrictions or obstacles causing this sort of reduction in width <strong>the</strong>y should be<br />
grouped in a logical <strong>and</strong> regular pattern to assist visually impaired people.<br />
It is also recommended that <strong>the</strong>re should be minimum widths of 3m at bus stops <strong>and</strong> 3.5m to 4.5m by<br />
shops though it is recognized that available space will not always be sufficient to achieve <strong>the</strong>se<br />
dimensions.”<br />
<strong>Trees</strong> <strong>the</strong>refore will never be planted in <strong>the</strong> footway when <strong>the</strong> tree (taking account of any expected<br />
incremental enlargement of <strong>the</strong> trunk) is likely to reduce pedestrian clearances to less than 1m. The tree pit<br />
itself cannot be included in <strong>the</strong> measurement of clear width unless <strong>the</strong> surface is useable by a wheelchair. If<br />
resin-bound aggregate is used as a pit surface, <strong>the</strong>n it can be classed as clear width, o<strong>the</strong>rwise <strong>the</strong><br />
measurement must be taken from <strong>the</strong> edge of <strong>the</strong> pit to <strong>the</strong> edge of <strong>the</strong> public highway (not necessarily <strong>the</strong><br />
building façade).<br />
<strong>Trees</strong> should not obstruct pedestrian sightlines. In general driver sightlines also need to be maintained,<br />
although avenue planting can be used as a tool to increase perceptions of speed <strong>and</strong> <strong>the</strong>reby limiting traffic<br />
speeds.<br />
New planting should consider <strong>the</strong> function of existing street furniture such as street lights <strong>and</strong> CCTV cameras,<br />
as foliage can block lights <strong>and</strong> images. Tree planting should respect <strong>the</strong>se primary functions, <strong>and</strong> where<br />
street furniture cannot be relocated, <strong>the</strong> location of planting should be reconsidered.<br />
Over <strong>the</strong> page are <strong>the</strong> arrangements found in typical streets in <strong>Westminster</strong>, <strong>and</strong> where trees could be<br />
planted within <strong>the</strong>m. Fur<strong>the</strong>r detail can be found in <strong>the</strong> <strong>Westminster</strong> Way public realm manual.<br />
When choosing a specific location in <strong>the</strong>se streets an important consideration is how content <strong>the</strong> tree will be.<br />
This includes how close to its natural proportions can it grow (it should be able to grow to at least look<br />
‘natural’), <strong>and</strong> what will it contribute to, or harm, in <strong>the</strong> street scene when fully grown, for example shade,<br />
pedestrian impediment, colour, obstruction of views or important buildings, or habitat for particular fauna.<br />
The ability of <strong>the</strong> tree to co-exist alongside services is a crucial factor. The size of <strong>the</strong> space available above<br />
<strong>and</strong> below ground will be a key factor in species choice. Pit dimensions should provide <strong>the</strong> tree with as<br />
much space to become established as far as is possible <strong>and</strong> practical given its location. New planting<br />
techniques have been developed to assist street tree planting where <strong>the</strong>re are space limitations, as is <strong>the</strong><br />
case in much of <strong>Westminster</strong>. Such techniques include <strong>the</strong> use of root barriers, or specially formulated<br />
topsoil allowing <strong>the</strong> creation of larger planting pits, essential for <strong>the</strong> planting of what could become a<br />
characterful tree. Detailed advice on this issue is contained in Tree Roots in <strong>the</strong> Built Environment (June 2006 -<br />
References in Appendix H).