External circulation and services
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The access system and general circulation pattern of a market will generally be the most critical aspect of its master plan and initially needs to be looked at as a complete entity. In reviewing external circulation components of a market development plan all aspects of transport that might serve the site need to examined. These will include
· road transport, including small-scale electric vehicles;
· rail links;
· rivers and canals;
· air (for export markets); and
· non-vehicular transport (pedestrian head loads and animal carts).
Road patterns. The ideal practice in developing a road layout is to strictly segregate the produce coming in from that going out, usually by adopting a one-way circulation system. Figures 7, 11 and 30 give typical site layouts of small-scale modern market facilities which attempt to meet these general objectives.
A typical approach to establishing the road network for a market site is to provide a continuous peripheral road system or "ring road", with the buildings located within the centre of the block. By using minor loop roads or branches (cur-de-sacs) that penetrate within the block, the size of the area served by the ring road can be increased and individual facilities can be directly served by the road system. An important advantage of the ring road approach is that it enables drivers to search for parking spaces and to correct mistakes.
At this stage in the design process a hierarchy of roads
should be established, reflecting the different intensity of use
of facilities. Junctions and intersections between different
grades of roads will need to be looked at in detail, particularly
in respect of sight-lines and the spacing
between junctions. Grid road patterns may be used, particularly for large scale markets, but loop systems are more suitable for simpler layouts. As a basic principle it will be better to avoid any crossroads within the layout and to make as many of the junctions as possible 3-way (T-junctions).
Site entry and exit One of the most difficult features to achieve in any site layout is sufficient road length at the site entry so that incoming trucks can slow down and be checked-in at the entry gate without causing backing-up onto the public highway. In larger markets a series of entry gates are often located adjacent to each other, served by a single entry road. This problem also occurs on leaving the site and often this is more critical as it may involve handling a peak discharge of small volume vehicles (typically pick-ups). A layout with more than one exit has obvious advantages in terms of traffic control, although this may create problems of security and management of documentation.
Projected traffic flows and parking requirements. The turnover of vehicles in a market, particularly those of retailers, is rapid and it is highly desirable that a sufficient number of adequately sized parking spaces are provided. For a preliminary layout a minimum of around Go m² per truck parking space should be used, excluding the main circulation. An overall minimum standard for the provision of parking places (trucks, pick-ups and private cars) should be 2 - 3 spaces per 100 m² of sales area.
For peak periods, however, this could easily be increased to 4 - 6 spaces per 100 m², which may require the provision of reserve parking areas a little remote from the market facilities. Ideally, unloading and loading facilities need to be directly adjacent to the main market building, but this will not always be possible. In general, the desirable maximum distance from a parking space to a market building should be 100 metres, but it may be necessary to adopt a figure of 200 metres for peak parking in overspill areas. The use of the overspill areas should be confined to market users with small loads to carry.
In preparing more detailed proposals for a site, estimates should be made of the projected traffic flows and distribution by type of vehicle. These may include producers' delivery vehicles, retailers' and other buyers' vehicles, transport for permanent and temporary market staff, and the vehicles of the general public Table ]3.13 gives details for the Kalimati site in Nepal of typical parking requirements for vehicular traffic at the peak period (assumed in this case to be the period when retailers are making their purchases). Appropriate parking and circulation design standards are discussed in Chapter 14.
For very large market sites, traffic models, using computers, are necessary for projecting traffic flows. For smaller markets, however, simpler techniques based on examining the pattern of traffic data from roadside and market surveys (see Chapter 11) can be used. Of particular importance is to understand the types of vehicles that are using a market and when peak periods may occur. Figure 32 shows the pattern of arrival for vehicles using the Birmingham (UK) wholesale market based on a 7-day survey.
13.13 Kalimati wholesale market: estimated number of vehicles per day and peak period parking requirements at ultimate development
|Retailers small trucks & pick-ups:|
|Add 22.5% for suppliers' vehicles/contingency*||17|
|Truck parking spaces required (@ 8m x 4m)||92|
|Add for wholesaler's cars (@ 5.5m x 2.4m)||8|
|Total parking spaces within the market||100|
|Private cars and official vehicles:|
|· One parking space for each senior official||12|
|· Add 150 % for visitors/general public||18|
|Car parking spaces required (@ 5.5m x 2.4m)||30|
|Add 20 % for short term truck parking (e, 8.m x 4m)||6|
|Total parking spaces outside the market||36|
Source: FAO (GCP/NEP/043/SWI)
Note: * Includes allowance for longer vehicles
Other services. Services other than roads can be disregarded in the initial preparation of the overall site plan, but as the site layout is gradually finalized, consideration will need to be given to the location of other service networks.
Because of the scale of open drainage systems and the significant runoff from paved market areas, surface water drainage is likely to be the most important service to consider next. The alignments of channels is likely to be a major constraint on the overall site layout because of the rigidity of design standards that will need to be applied. Invariably, the issue of off-site disposal of surface water and how it can be related to existing natural drainage lines will also have an important influence on the detailed planning of the site.
Figure 32 Mean arrival times for vehicles delivering to Birmingham wholesale market
The majority of other services are likely to be placed underground, but these networks need to be co-ordinated with each other for ease and economy of construction and in order that future maintenance does not disrupt the working of the market. The use of "common" trenches for the distribution of services, which establish precisely both their vertical and horizontal relationships, is often adopted.
Environmental impact and controls
Although the site layout should take into account the servicing requirements of the market there are a number of environmental problems associated with site development which may need to be resolved at the detailed design stage. 1 he following notes review the types of site-level environmental problems and the general solutions that may be encountered in market development. More detailed engineering design criteria are described in Chapter 14.
Surface water drainage. The technical issues associated with the disposal of surface water from market sites are not difficult if tackled properly. The surface water drainage system will need to deal with storm water flows for peak discharge conditions and the method for estimating this is described in Chapter 14. However, severe problems may occur if a substantial amount of filling is required to bring the site above flood level or to provide a more stable base for construction. This will need to be carefully addressed in order to avoid impacting on the adjoining sites, causing backing-up of drainage water at upstream sites or direct flooding downstream.
Information on actual recorded flood levels may not be readily available and an interview survey of local residents may be required in order to establish the level and duration of previous floods and the likely "return periods,' (the time intervals between occurrence of storms of similar intensity). Solving potential flooding problems often requires that off-site works are undertaken These will need to be incorporated into the market development programme.
Market sites must be almost completely paved and the critical factors to take into account when calculating the drain sizes and sections will be the gradients, the need for frequent cleansing of drains which are easily blocked by produce waste (open channels are normally either covered with steel gratings or concrete slabs) and any potential restriction created by the existing site discharge.
Water supply. Water supplies to markets are required for drinking and sanitation purposes, for general cleaning and, in some cases, for the washing of produce. If an existing mains supply is available this would normally be used, although some improvement to the mains may be required in order that the site can be served. Often, the only practical solution to the supply of potable water for a market will be to use a pumped supply from a bored tube well, with an on-site storage tower.
To obtain a guaranteed supply, sample borings may be required. If an adjacent site is already occupied then useful information can be obtained by discussions with the adjoining owners to investigate what problems, if any, they have experienced. A water-quality analysis of any existing supply may be required to test for the presence of pollutants, particularly faecal coliform bacteria (Escherichia coli).
Techniques for the construction of tube wells and other small-scale supplies, which may be appropriate for secondary wholesale markets, are given in the Ross Institute Bulletin No. 10 (Cairacross, S. & Feachem, R. 1978. Small wafer supplies. London School of Hygiene & Tropical Medicine). Usually a drilling or excavation permit will be required before constructing a new well or other form of supply.
Sewage treatment. Markets, like any other facility used by the public, will require the provision of toilet facilities A conventional water-borne sewerage system using an existing mains connections is often not available for market sites and some form of on-site treatment will be necessary. The purpose of the system will be to remove organic (excrete) waste so as to prevent infection transmission, pollution of receiving water courses, development of odours and breeding of files, typically Psychoda. National effluent guidelines frequently require that markets install their own treatment systems and this is usually enforced through building permits. Market sites, however, arc normally not large enough to justify a mini-treatment plant and there are major ¿difficulties in the maintenance of such complex electrical and mechanical systems
Other options available include waste stabilization ponds, aerated lagoons and oxidation ditches These are unlikely to be appropriate for the relatively small-scale requirements of a market. They may, however, be warranted if the market is to be developed in conjunction with other facilities, in which case their economic viability will need to be assessed Suitable design criteria are given in Overseas Building Note No. 174 (Mare, D. 1977. Sewage treatment in ho' countries. Garston, Building Research Establishment).
In many cases, a septic tank system, with leach fields and partially treated effluent going to surface water drains is likely to be the most practical, economic and environmentally satisfactory solution. An agreement will need to be made with any local sanitary board for the collection of solids and periodic cleaning of the septic tank. The location of the septic tank should be away from any adjacent sensitive uses and close to the existing surface-water discharge A minimum distance of 30 metres should be maintained from any wail, 7 5 metres from streams, 3 metres from water pipes and 1.5 metres from buildings or boundaries. Estimating the capacity of the septic tank will depend on the numbers of sanitary fittings, which is discussed in Chapter 14.
For small secondary wholesale markets in rural areas simpler methods of excrete disposal are normally adopted. These are, typically, pit latrines and aqua privies. A full review of these techniques is contained in the Ross Institute Bulletin No. 8 (Feachem, R. & Cairncross, S. 1978. Small excreta disposal systems, London School of Hygiene& Tropical Medicine).
Disposal of solid waste. Refuse is potentially a major cause of environmental problems. These range from public health risks, fire hazards, odours and nuisance from burning and the polluting of ground and surface water sources. The management of solid waste is thus a key issue that will need to be resolved.
The waste generated at a market will have a high organic composition (minimum 50 percent), with a high moisture content (60 - 70 percent) and a low calorific value (+/- 1,000 kcal/kg.). Small-scale incineration is not practical or economic, nor advisable given the potential environmental impact it might have on adjacent sites. On-site compaction of waste and pressing into a container is not likely to be viable in developing countries, although it is an attractive solution for reducing transport demands and disposal facilities.
Waste should therefore be collected for disposal off-site. If the market's solid waste problems cannot be handled by the local collection authority then it may be necessary for the market to consider setting up its own facilities, either for recycling the waste as compost or by a controlled tipping or sanitary landfill operation. Techniques for this are reviewed in Flintoff, F. 1976. (Management of solid wastes in developing countries.. New Delhi, WHO Regional Publications, South-East Asia Series No. 1).
Equipment options for collection and methods for calculating the volumes of waste that might need to be handled are given in Chapter 14.
Noise nuisance. Noise levels at markets can cause a significant public nuisance, particularly given their extended hours of operation. Data from a survey by Chiang Mai University (Paiboonslip, P. 1985. Noise monitoring in Chiang Mai) indicated that one of the main retail markets had the highest ambient noise level, 81.16 decibels [dB(A)], of any site surveyed in the city. For this reason market sites are usually located away from residential areas and other sensitive land uses. If an existing site is adjacent to such uses careful design measures will need to be adopted in upgrading the market.
Community ambient noise standards may not exist and adopting those used in developed countries may be inappropriate. The Initial study findings report of the Chaing Mai Planning Project (Louis Berger International Inc. 1991) suggested the following standards, based on Japanese levels (but around 15 dB[A] higher), for areas where there is a special requirement for quiet conditions such as schools, religious buildings and hospitals:
|Maximum noise level||60 dB(A)||55 dB(A)||50 dB(A)|
It is usually assumed that the noise levels will apply at the property boundary. Another approach often adopted is to categorise land uses according to their sensitivity to changes in the ambient noise level. For example, no increase above approved noise levels for 90 percent of the time in residential areas might be permitted and only a marginal increase allowed in rural areas or those of mixed use. A significant increase in noise levels may be allowed for developments on industrial sites.
There are a number of ways the noise impact of a market development may be reduced, with different cost implications and effects on a market's operating system. This issue will need to be carefully considered during detailed design:
· distance attenuation, by siting noisiest uses away from sensitive areas. In open air, noise decays at a rate of around 6 decibels (dbA) per doubling of distance from the sound source (the decibel scale is a relative measure on a logarithmic base, giving a ratio of sound pressures);
· restricting the working hours of a market, so that for example the impact of heavy traffic early in the morning is minimized;
· attenuation by screening. The construction of walling around a site will have a significant impact on noise levels, particularly higher frequency sound. Problems that this might create in terms of pollution and climatic comfort levels are discussed below; and
· attenuation by window design, by modifying the windows of adjacent buildings, using double glazing combined with mechanical ventilation or by adding projecting external fins, both of which can have a considerable impact on internal ambient noise levels.
Air pollution. In the humid tropics, if sites are fully enclosed by high walls this might have a number of detrimental effects. Air flow will be restricted and this will hinder natural ventilation both within the market and of adjacent uses, leading to uncomfortable internal conditions. Equally important, however, will be the problem of containment of air pollutants as the construction and operation of any market will lead to a significant increases in pollution levels.
This may be acceptable in arid areas, as the general conditions for obtaining a reasonably comfortable working environment will require that as much shade is obtained as possible. For the humid tropics, however, it would be better to confine environmental improvements to the optimum siting of facilities, planted screening (which will have little impact in terms of noise attenuation) and the upgrading of windows. Allowing vehicles to enter the market building, as in some layouts where the buyers' walk is made wide enough for vehicles, is not considered to be acceptable in either the humid tropics or arid climates.
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