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PIM POR BETTER TUR11-1110WID
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by Jolyon Drury, MA, Dip Arch {Cantab), MIMH.
An architectural consultant with transport experience advises on the provision of transport receipt and dispatch facilities at premises
SLOW turn-round times generated by congested manoeuvring areas and selfstrangulating loading bays are a common complaint of both haulage contractors and own-account operators. There is a conflict between the careful thought that is seen in purchasing high-specification trucks. matched to their duties, and the low-key thinking that is applied to planning the area where loads are handled.
Much unnecessary waste of earning potential can be eliminated by correct planning of receipt and dispatch facilities. Particular care should be taken when considering the interface between zones, as it is the failures of interaction here that generate very high hidden costs.
Three closely inter-related zones, which must not be considered in isolation, are: 1, approach and manoeuvring area; 2, loading bay, its equipment and environment; 3, zone behind the loading bay.
One area where short-term expediency as against long-term value is particularly apparent is in the provision of space for manoeuvring and accumulation. Yards are seen where drivers perform superhuman feats to manoeuvre a 15m artic into a constricted bay position. This leads to the common argument that if the drivers can get in, why waste money on expensive land? This is a false economy. The time taken to position a vehicle is time wasted on turn-round.
If an arrival peak occurs, a constricted area is soon full of vehicles impeding each other.
One example (figure 1) is a company that correctly routes a one-way flow round a warehouse, which has Customs clearance facilities; delivery and dispatch bays are segregated. Often, empty vehicles wanting to pass through to the dispatch zone are blocked by the queue waiting for a place to unload under Customs supervision; the roadway is further constricted by piles of crates and large equipment, too big for normal handling.
Loading bays Careful thought about the orientation of the loading bays in relation to the entry roads could have avoided this; there are always loads that are abnormal in some way, so provide clearly marked areas for them.
Where the numbers of vehicles are expected to exceed that of the loading bays, provide accumulation lanes. Some sorting out is then possible to avoid the time-wasting melee as trucks shunt to find the right bay.
Another example is where an area allotted for parking full semi-trailers and containers before unloading has been inadequate even for immediate needs. This was partly due to lack of foresight, and partly to inefficient handling on the dock reducing the predicted speed of throughput. The shunt driver had to park trailers so close that a tilt trailer had to be literally shunted into a gap.
Do not forget that when vehicles are parked in tight rows the lack of cut-in-space precludes immediate turning; with a 3.7m-wide bay, there is a need for at least 5.7m draw-forward before a turn can begin. With a normal swept turning radius of 13.4m, at least 33.4m is required from the dock face to the outer edge of the tractive unit with 90 degree docks, and at least 21.3m if the dock is angled at 45 deg. Even these dimensions do not allow other vehicles to manoeuvre simultaneously. (See figures 2 to 6.)
The increasing popularity of draw-bar trailers demands more space still. While some European drivers can reverse drawbar outfits into a loading bay, this is an optimistic assumption to make. Many units are seen to unhitch, turn round, and nose the trailer into the dock; 40m and more is suggested for drawbar work with 90deg docks, if other traffic is not to be hindered.
Routeing light vans A problem that faces both groupage operators and parcels carriers is routeing the numbers of light vans. Peaks quickly result in jams, where light vehicles get caught between the heavy trucks. To prevent stoppages, light vans should be segregated at the gate: a few clear signs and road markings are notextravagant, and a second approach lane is justified by the accelerated handling.
Should the dock be raised or at road level?
What angle should it be? These decisions are a compromise between: O Required throughput.
▪ Predicted peak flows.
O Manoeuvring area available.
O Type of vehicle.
O The handling demands on the dock.
O The type of operation involved.
The type of company using the facility is a fundamental influence on these factors. For example, a general haulier occasionally having to store a few pallets is justified in operating ground-level loading, especially if flat trailers predominate; so is a steel stockholder unloading coil with an overhead gantry crane. As a rule, however, raised docks have many more advantages than ground-level facilities: this can be achieved at little extra cost by using the topography of the site to advantage.
Groupage operators have a particular problem; there is a conflict between container stuffing demands and loading TIR tilt trailers. Container work is more efficient from a raised dock; loading ramps, although expedient, are space consuming in that they must not exceed a gradient of 1 in 10; they also need space to be allocated for their own storage. The present generation of British TIR trailers tend to preclude raised dock loading, however, as the conservative haulage industry did not want to pay for floors capable of accepting fork-lift truck wheel loadings.
It is true that increasing numbers of manufacturers are marketing trailers with this capability, but the problem is with us, generating ground-level loading and demanding an area for rolling back the tilt, removing hoops and side panels. The situation is further confused by the European trend towards drop-well tilt trailers for maximum volume within the proposed 4m height limit in the EEC.
At present the unsatisfactory situation is compelling groupage operators to make a difficult decision; they must plan a raised dock or ground-level facility on the basis of predictions of whether containers or tilt trailers will provide the bulk of their business in the future.
Light feeder vans for parcels carriers and groupage are better handled from the floor. Provide these vans with a segregated handling area for manual off-loading, with sufficient space behind each van for the drivers to spread out the dispatch load to sort into the order of drops best suited to the local traffic conditions. From 3.5m to 5m behind each van is suggested.
Should there be combined or separate delivery and dispatch bays?
This again depends on the type of business but is also affected by the peak situation. Predicting peaks is never easy, especially in distribution, with seasonal and weekly variations in the market. Consider the peak predictions also in terms of the utility of the handling plant and the traffic flow. This will help decide the benefit of a single or dual-duty bay: there is more chance of a peak jam in a dual-duty bay, but segregated bays duplicate equipment that is likely to stand idle for much of the time. The operator must decide where the priority lies.
Suppliers' vehicles
A factor often neglected by own-account operators is that suppliers' vehicles are often larger than their own. One installation has the incoming supplies bays grouped at the entry end of a 90deg. totally enclosed dock area. Because of this a weighbridge was positioned opposite these bays; the operator employed 9m rigid vans, and the turning area was sized for this. Suppliers arrived with 15m artic vans, with the result that when one was in the bay, and another on the weighbridge, none of the operator's trucks could enter. Of course, this always happened during the busiest peaks!
Angled docks are useful in constricted premises. The number of docks is sacrificed at the expense of about a third less depth from the face of the dock. Angles have been suggested from 30 deg to the FTA booklet's 50 deg: the angle should be tailored to the vehicles and the space available; the direction of the angle should be commensurate with the direction of traffic flow — clockwise, and in reverse anti-clockwise, in Britain (the opposite in right-hand drive countries).
To solve the groupage conflict, finger
docks (figure 5) can be successful. Although longitudinally space consuming, a finger dock at 80 deg allows:
1, conventional end-loading for containers; 2, over-the-side loading of tilt trailers from dock level; 3, ground-level loading of outsize items; 4, quick manoeuvring even for drawbar outfits.
The sacrifice of numbers of bays is compensated by the speed of throughput. Another conflict is that many groupage depots may soon handle more Continental outfits than British; in this case it might be worth building the dock to the European rule of the road.
How wide should each bay be?
The FTA published a useful booklet setting out guide dimensions. Although in isolation these are not questioned, in practice there are differences. The FTA suggests a 3.3m bay width as minimum. First, the narrower the bay, the greater the draw forward; secondly, bay spacing should not be just a function of vehicle clearance, but of handling behind the dock. Consider fork-lift and pallet truck manoeuvring and passing clearances.
Four metres spacing is preferable, with 5m bays if dual-purpose bays are used, with peaks requiring rapid roll pallet clearance. This is not an extravagance: fewer bays and quicker turn-rounds are more cost effective than tight spaces and self-strangulating organizations.
Critical link
The loading bay is the critical link element between the storage and distribution systems. The efficiency of this zone relies on the choice of handling plant and loading bay equipment matched to the particular operating needs. Do not consider dock levellers as an optional extra; they make an important contribution. Truck bed heights are increasingly varied; in the past 10 years bed heights have risen from 1m to 1.55mm for a reefer container on a skeletal. It is not just a case of buying a leveller "off the peg" either; the spin-off costs from handling plant unsuited to the leveller type can offset any savings.
At no time should the gradient exceed 1 in 10, or the duration between fork-lift battery charges be reduced, there is increased battery wear, and loads become unstable. Remember that springs can rise 150mm during loading: the leveller must be able to cant with the truck, or there will be increased fork-lift tyre bills, and goods will be shaken off pallets. The manufacturers give gradient advice.
There are basically three types of leveller. Counter-balanced units are cheap but tend to bounce under load; mechanical spring-loaded types are the most popular in Britain, allowing very shallow pits and low maintenance, long life; hydraulic levellers, the norm in Europe, are more expensive, but are suitable for heavy-duty work and environments where the "clang" of a mechanical leveller dropping on to the truck bed is unacceptable, where there is night loading in a housing area for instance. With the present high cost of builders' work for constructing pits (seldom included in manufacturers' quotations), there is the option of semi-free or free-standing levellers, useful also for converting existing premises.
For groupage, where occasional container work does not justify a raised dock, and also useful at own-account operator's premises and for quickly equipping old facilities, are mobile lift tables and elevating docks. The former is a scissor lift on a mobile base, the latter similar but with a lower profile when retracted.
Damaged tail-lifts
One distribution company has experienced so many vehicles out of commission through damaged tail-lifts that each major store is to be equipped with a mobile lift table and they will revert to standard vans. Versions capable of lifting 10,0001h, a fork-lift and pallet, up to a container door are available — a useful alternative to expensive container lifting gear.
Another variation is the mobile dock leveller: this allows trunk vehicles to position freely in constricted bays, or where feeder vans get in the way. The leveller, fixed to a mobile frame mounted on rails plugged to the dock face is rolled to the
truck, saving a lot of shunting time.
What about the environment of transport facilities?
A canopy is money well spent, saving damage to goods and ensuring all-weather working. The canopy should extend 3 to 3.5m from the dock face, and for 8ft 6in containers on skeletals should allow a clear height of 4.6m. Dock shelters are a useful alternative where rigid environmental control is required at the rear of the vehicle, such as for cold store work.
Often neglected is the need to provide a high, glare-free light level; 40ft containers are too long for natural light penetration,. and their own lights are often broken. Dock lights on adaptable stalks, spring-mounted against impact, are useful, but take care that they do not become direct or reflected glare sources: this can cause disorientation and accidents.
Fume extraction is normally required only for totally enclosed bays but should be installed where perishables could be contaminated. Some cold store operators have been worried by high levels of fume build-up under canopies from the refrigerated trailers' donkey engines. Extract at high level, making sure that the exhaust is far from any inlets.
On-dock circulation
All this planning can come to nought if on-dock circulation is not considered as an integral part of the system from the outset
(see figures 7 and 8). It is this that often determines the loading bay width. Although this is largely outside the scope of this article, relying on the demands of the storage medium and the handling plant to suit it, in brief, space must not be skimped for fork-lift manoeuvring and cross-flow. Do not place equipment like weighing machines in the main circulation route. Allow space for repacking unstable pallets and removing broken units. How many readers have corners of their yards full of old pallets and drums? A conveniently placed rubbish skip and an area allocated as a pallet store should be provided.
It is in the interest of both the user and provider of road transport to hasten turn-round times. The planning of any transport facilities must be considered as part of the total distribution system from the outset. Many unnecessary failures of interaction have been caused by users not asking for transport operators' requirements, and by supplying equipment manufacturers with inadequate briefs. In several new facilities, it has been suspected that what was really needed was reorganization of the distribution system. There is a need for the distribution industry as a whole to care more about the long-term strategy of providing efficient transport facilities, and less about short-term expediency.
As the well-known slogan says; "Why settle for less? You know it makes sense!"