Opportunities for Consolidating Volume-constrained Loads in Double-Deck and High-Cube Vehicles.

Transcription

1 Opportunities for Consolidating Volume-constrained Loads in Double-Deck and High-Cube Vehicles. by Professor Alan McKinnon and James Campbell Christian Salvesen Logistics Research Paper No. 1 Heriot-Watt University, Edinburgh, EH14 4AS. Tel: Fax: A.C.McKinnon@hw.ac.uk February 1997

2 EXECUTIVE SUMMARY This paper is concerned with the utilisation of vehicle space. It argues that there is considerable potential for making better use of the cubic capacity of lorries, thereby cutting the cost of road haulage and reducing its impact on the environment. Many low density products fill the available vehicle space long before the maximum legal weight is reached. Given the tight limits on the height to which most products can be stacked, loading is usually constrained more by the available floor space (or deck area ) on the lorry than by its total cubic capacity. The insertion of an upper deck into lorry trailers relaxes this constraint and permits greater load consolidation. It is generally acknowledged that the average density of loads is diminishing. This appears to be the result of changes in the nature of products, increases in the amount of packaging material and greater use of unitised handling equipment. At the same time the height to which loads are stacked is also declining. Over the past 15 years the maximum permitted weight of articulated vehicles has increased by a greater margin than their cubic capacity and deck area. It is likely, therefore, that an increasing proportion of loads are volume-constrained and likely to benefit from greater use of a double-deck / high-cube vehicles. It is difficult to assess the potential for these vehicles in the absence of volumetric data on road freight flows. The main source of road freight statistics in the UK, the Continuing Survey of Road Goods Transport, measures payloads solely in terms of weight. Nor are there any official statistics on the numbers of double-deck or high-cube vehicles currently on UK roads. One estimate suggests that there are around 1000 double-deck vehicles, representing only 1% of articulated lorries with gross weights over 28 tonnes. This paper focuses on possible improvements to the cube utilisation of 32½ tonne articulated lorries by double-decking, and in some cases, enlarging them within current vehicle size limits. Much of the double-decking would, however, occur within trailers of standard dimensions. At present the average lading of 32½ tonne artics, at 49% of maximum weight, is well below that of 38 tonne artics (70%). This is largely because the 32½ tonne fleet is used predominantly to carry less dense loads. It is hypothesised that by double-decking / enlarging these vehicles it might be possible to raise their average lading factors, for particular commodities, to the same level as 38 tonners. An attempt was made to calculate the benefits of bringing lading factors of 32½ tonne artics into line with those of 38 tonners for ten targeted commodity groups. This would reduce the annual distance travelled by 32½ tonne artics by 525 million vehicle-kilometres, equivalent to approximately 5% of all articulated lorry traffic. As it costs roughly 1.05 per mile to operate a 32½ tonne artic, a gross saving of 340 million per annum might be made, though it would be necessary to deduct from this figure the extra costs of acquiring and operating double-deck / high-cube trailers. While their capital costs are significantly higher than those of conventional trailers, this cost differential is narrowing. For standard curtainsided trailers, the cost penalties appear small relative to the 40% increase in usable volume that double-decking typically permits. The estimated reduction in the total annual distance travelled by 32½ tonne artics would cut emissions of CO 2 by around 510,000 tonnes, nitrogen oxide by 11,000 tonnes, black smoke by 3000 tonnes and particulates (PM10) by 440 tonnes. Noise irritation, road-side vibration and accident levels would also be reduced. These environmental benefits would have to be set against any increase in visual intrusion resulting from greater use of high-cube vehicles. Much of the load consolidation, however, would be achieved by double-decking standard trailers. The estimated savings in vehiclekilometres make no allowance for the possibility that the reduction in road transport costs might generate additional freight movement or divert traffic from rail, with consequent losses of environment benefit. It is reckoned, however, that these effects would be quite marginal. 1

3 Table of Contents 1. Introduction 1 2. Physical Limits on Vehicle Loading 2 3. Load Density of Goods in Transit 3 4. Design of Double-Deck and High-Cube Trailers 5 5. Analysis of the Potential Use of Double-deck / High-cube Trailers 7 6. Economic Benefits from Increased Use of Double-deck / High-cube Trailers Environmental Benefits from Increased Use of Double-deck / High-cube Trailers Implications for Articulated Lorries Over 32½ tonnes Conclusions 19 References 20 Tables Table 1: Lading and Empty Running by Vehicle Type, Table 2: Tonne-kilometres and Vehicle Lading Factors for Different Commodities, Table 3: Potential Savings by Commodity from Improved Lading of 32½ tonne Artics 11 Table 4: Potential Contribution of Targeted Commodities to Total Savings. 12 Table 5: Potential Savings from the Improved Space Utilisation of Articulated Vehicles 13 Table 6: Comparison of Conventional and Purpose-Built Double-deck Semi-trailers 15 Table 7: Estimated Annual Reduction in Emissions 16 Figures Figure 1: A Taxonomy of Double-deck Semi-trailers 7 Figure 2: Tonne-kilometres Carried and Lading Factors of 32½ and 38 tonne Artics, 1980 to Figure 3: Low Density Commodities Share of Total Road Tonne-kilometres, 1986 to Acknowledgements This project has been financed by research sponsorship from Christian Salvesen plc for the study of transport and logistics issues at Heriot-Watt University. The views expressed in the paper are solely the responsibility of the authors. We are grateful for the assistance of staff in the following organisations in the preparation of this paper: Department of Transport, Freight Transport Association, Marks and Spencer plc, National Environmental Technology Centre, Scotch Whisky Association, Swift Transport Services, Whitbread Drinks Logistics, Wilson Double-Deck Trailers. February

4 1. Introduction In its Green Paper on Transport, published in April 1996, the Government stated that, The central direction of policy on freight transport must be to make better use of our existing assets, both infrastructure and vehicles, recognising that environmental pressures are likely to increase in the longer term [Department of Transport, 1996a]. This applies particularly to the movement of freight by road, given the worsening problems of traffic congestion and environmental pollution. One of the most obvious ways of increasing the utilisation of the nation s lorry fleet is to improve vehicle lading. Analysis of the available statistics on vehicle lading suggests that there is currently a substantial amount of surplus capacity in the road freight system. The lading of a vehicle is defined as the ratio of the tonne-kilometres 1 that a vehicle actually carries to the tonne-kilometres it could have carried if on every loaded trip it was running at its maximum gross weight. The average lading factor of many categories of vehicles is relatively low (Table 1). Across the lorry fleet as a whole, only around 63 per cent of all the capacity to carry tonne-kilometres on loaded trips in 1995 was actually utilised. If allowance is made for empty running, this utilisation figure drops to 44 per cent. Table 1: Lading and Empty Running by Vehicle Type, 1995 Vehicle type and weight: (tonnes) Lading factor (%) Empty running (%) Lading factor, including empty running (%) Rigid vehicles: 3.5 to Rigid vehicles 7.5 to Rigid vehicles 17 to Rigid vehicles over Average for rigid vehicles Articulated vehicles 3.5 to Articulated vehicles over Average for articulated vehicles Average for all vehicles Source: Continuing Survey of Road Goods Transport, 1995 Efforts to increase the average lading factor are limited by three factors: 1. Scheduling of deliveries: The size and weight of consignments is determined by the scheduling of production and distribution operations and the order replenishment process. To meet the requirements of production and marketing strategies, transport managers have often to despatch loads that only partially fill a vehicle. 1 A tonne-kilometre is defined as one tonne of goods being moved one kilometre. 3

5 2. Drivers hours restrictions: Shift patterns and legal restrictions on drivers hours limit the amount of freight that can be delivered on a single journey, particularly in the case of multiple-drop rounds. 3. Cubic capacity and deck area of the vehicle: Many low density products fill the available vehicle space (or cube out ) long before the maximum weight limit is reached. Where there are tight limits on the height to which products can be stacked, the main constraint is usually the deck area (the amount of floor space on which to place goods). The total deck area of a vehicle can, for instance, be covered with pallets stacked to a height of 4 feet leaving a further 8-10 feet of wasted space between the top of the pallet and the roof. This paper focuses on the last of these three constraints, considers how it might be relaxed and assesses the resulting economic and environmental benefits. 2. Physical Limits on Vehicle Loading Very little of the research on road freight operations has examined the cube utilisation of vehicles. This can be attributed to the lack of volumetric data on road freight flows. The main source of statistics on the movement of freight by road in Great Britain, the Government s Continuing Survey of Road Goods Transport (CSRGT) [Department of Transport, 1996b], measures quantities of freight transport solely in weight terms. It is for this reason that aggregate measures of vehicle utilisation are always based on consignment weight. Some light was, nevertheless, shed on the (cubic) volume of freight moved in a survey by Mackie and Harding (1983) which estimated that 26.7 per cent of loads were volume constrained and a further 16.7 per cent both weight and volume constrained. Altogether, 43.4 per cent of loads were limited, at least in part, by volume. The volume-constraint can be relaxed by enlarging the vehicle, in most cases vertically. This is only beneficial, however, for loads composed of products that can be stacked to a greater height. Where stackability is limited, the insertion of an upper deck can achieve a much greater increase in vehicle loading. The evolution of the passenger bus illustrates the potential advantages of splitting a vehicle horizontally through the addition of a second deck. In some cases, the full benefits of double-decking can be obtained without any increase in vehicle dimensions. With some products and handling systems, it is more efficient to combine the addition of a double-deck with some enlargement of the vehicle body. Many companies already employ double-deck trailers in the UK. Large retailers, such as John Lewis and Woolworths, use them for shop deliveries carrying two layers of roll pallets within a single vehicle. Other manufacturers and distributors, such as Whitbreads and Unipart, are also major users of double-decks. While some of these double-deck operations are conspicuous because of the magnitude of the vehicle, the double-decking of standard semi-trailers is not. As firms do not have to specify whether or not a vehicle has a double-deck at the time of registering, there are no official statistics on the number of double-decks currently on British roads. One of the major trailer manufacturers, however, has estimated this number to be 4

6 around This would represent roughly 1 per cent of the total of 94,000 articulated vehicles with a gross weight of over 28 tonnes. This paper predicts that this proportion will increase over the next few years as a result of several developments: 1. Advances in vehicle technology: Leading to improvements in the design of double-deck trailers and narrowing of capital and operating cost differentials with conventional vehicles. 2. Increasing road transport costs: Resulting primarily from increasing traffic congestion and the imposition of environmental taxes. 3. Economies of scale: As the market for double-deck and high volume trailers expands, scale economies in vehicle manufacturing will drive down unit costs. 4. Increase in maximum lorry weight: To exploit fully a maximum weight increase to 40 tonnes in 1999 and possibly, at later stage, to 44 tonnes, many operators will require additional deck space. 5. Decline in load density: As the average physical density and permissible stacking heights reduce, firms will be forced to give greater priority to the cube utilisation of vehicles. The decline in load density is of particular interest and is examined further in Section Load Density of Goods in Transit It is often claimed that the average density of road freight has been declining. In the absence of volumetric data on freight flows, this cannot be substantiated empirically, though it seems likely to have occurred as a result of six trends: 1. Change in the nature of the products: Many consumer products have become lighter through time, as plastic and other synthetic materials have increasingly replaced metal, wood and leather. The miniaturisation of components has also reduced the weight of many appliances. A new generation of products has emerged, in sectors such as electronics, sports equipment, toys and DIY, which are intrinsically of low density. The substitution of mechanical and electro-mechanical machines by microelectronic devices has also reduced the weight of a range of appliances. In the food and drink sector, an increasing proportion of food is being purchased in a lighter processed form while the gradual shift from kegs of beer to canned and bottled beer and lagers is reducing the amount of liquid that can be transported in each square metre of vehicle space. 2. Increase in packaging: During the post-war period, the move to self-service retailing, the growth of processed food and the more intensive use of packaging as an advertising medium have greatly increased the amount of packaging. Many of the new electrical and electronic products are also very fragile and 5

7 require thicker layers of protective packaging. As this packaging is very light, increases in the ratio of packaging volume to product volume reduce the average density of freight consignments. The growth of the packaging industry and increase in the amount of packaging material being recycled has also generated many more lorry journeys carrying very low density consignments of cardboard, polystyrene and other light-weight packing materials. 3. Greater use of unitised handling equipment: The growth of palletisation and increased use of roll / cage pallets has enabled firms to improve the efficiency of handling operations at the expense of vehicle utilisation. This handling equipment takes up space in the vehicle and again reduces the average weight : volume ratio for the overall payload. 4. Reduced stackability: In some sectors, the increasing fragility of the product and weakening of packaging material is limiting the height to which it can be stacked. In the food and drink industry, for instance, cans have become thinner and rigid cardboard, plastic, or even wooden boxes been replaced by cardboard trays which offer no vertical support. 5. Order-picking of palletised loads at an earlier stage in the supply chain: Traditionally, the primary distribution of manufactured products from factory to distribution centre was supply-driven, with pallets loaded to maximum height with a single product line and standard packaging. These pallets could often be stacked to form a dense load within the vehicle. The single line pallets would be broken down and individual customer orders picked further down the supply chain at an intermediate depot closer to the customer. The growth of quick response and cross-docking is now forcing manufacturers to assemble mixed orders for individual retail and wholesale customers either at the plant or central warehouse. The flow of product at the upper levels of the supply chain is thus becoming demand-driven and pallet loads tailored to customer requirements. These pallet loads tend to be lower, have an irregular profile and offer less opportunity for stacking. Customer-picked pallets thus tend to make less efficient use of the available vehicle deck area and cubic capacity. 6. Tightening Health and Safety Regulations: These regulations have restricted the height to which pallets can be stacked to minimise the risk of injury to operatives during loading and unloading. This again, however, has the effect of reducing the amount of freight that can be carried on each square metre of deck area. The first three trends reduce the physical density of freight consignments, while the second three limit the height to which products can be stacked in transit. They all threaten to reduce the utilisation of existing road freight capacity. It was mentioned earlier that the survey undertaken by Mackie and Harding in the early 1980s suggested that 43.4 per cent of loads on articulated vehicles were limited by volume. No indication was given, however, of the extent to which the volume-constraint was actually a deck area constraint. Since then the maximum dimensions of semi-trailers has increased, mainly as a result of the length limit going up from 40 to 44 feet, offering a 10 per cent rise in deck area. The maximum permitted weight has, however, increased by a much greater margin from 32.5 to 38 tonnes. The fact that the weight limit has increased much more that the size limit, together with the declining density and stacking height trends outlined above, 6

8 would suggest that an even larger proportion of loads may be constrained by volume today. The potential benefits of inserting of an upper deck in road vehicles are likely, therefore, to have increased. 4. Design of Double-Deck and High-Cube Semi-Trailers Double-deck semi-trailers can be adapted from a conventional vehicle simply by adding a second deck half way between the roof and the floor (figure 1i). Such conversions can, however, give rise to a number of technical difficulties. Careful design of the vertical bulkheads (or centre pillars where a rotating upper deck is used (figure 1ii)) is vital, particularly in the area of the joint with the existing floor. This is necessary to ensure that the continuous cycles of acceleration and retardation applied to the load on the upper deck do not produce a moment (that is a turning force such as a spanner applies to a nut) such that the lower joint would eventually be liable to a (catastrophic) fatigue failure. For at least the past ten years it has been possible to purchase purpose-built double-deck trailers from specialist suppliers. These trailers replace the traditional twin I beam chassis with a light weight, complex arrangement of box section steel tubes and fabricated sub-assemblies. Customised floors have also been developed which can support standard loads but are of much thinner construction, as slender as 50mm. This has helped to minimise any tare weight penalty. Purpose-built trailers have also been enlarged to maximise the potential benefit of double-decking. This has been achieved by: 1. Increasing the height of the trailer: A cost effective method of increasing volume but limited by vertical clearances on the road network and handling restrictions. 2. Lowering the floor of the trailer: The adoption of smaller road wheels, possibly running in boxed arches that encroach into the body, coupled with a swan neck or step frame trailer design can permit a lowering of the floor by 400mm (figure 1iii, 1iv & 1v). The use of a low chassis tractor unit running on low profile tyres would offer a 200mm drop in the fifth-wheel height and hence the floor of the trailer over the tractor unit. Both seek to make better use of the dead space between the tractor unit and the road wheels of a conventional tractor / semi-trailer articulation. 3. Eliminating beam axles on the trailer: At least one double-deck manufacturer has developed a stub axle located by a swing arm which eliminates the need for a beam between the road wheels on trailer axles (figure 1vi & 1vii). This permits the use of a standard hub and break assembly, with super single wheels running in boxed arches. So arranged, the trailer floor can drop down below the centre line of the wheels, even on to the ground if required. These high-cube, purpose-built double-deck trailers are available as boxvans or curtain-siders and can include a movable upper deck which can be set at a standard semi-trailer deck height or in an elevated position to give full access to the lower deck (figure 1iix). It is claimed that, by using such technology, 7

9 sufficient head-room can be achieved over both decks to enable the use of standard 6 roll cages, keeping the overall trailer height within the 4 metre limit required by many European Union member States. The UK sets no legal height limit; most roads can accommodate vehicles up to 5 metres tall. Figure 1: A Taxonomy of Double-deck Semi-trailers. i) Conventional semi-trailer ii) Conventional semi-trailer with with fixed DD. 3 section rotating DD. iii) Swan neck semi-trailer with DD. iv) High volume swan neck semitrailer with boxed arches & DD. v) Swan neck semi-trailer with vi) Very high volume semi-trailer partial DD. stub axles and boxed arches. vii) Very high volume swan neck iix) Very high volume swan neck semi-trailer with stub axles, boxed semi-trailer with stub axles, boxed arches and DD. arches and movable DD. 8

10 Many firms carrying products of low density but high stackability employ high-cube trailers without an additional deck (figure 1vi). It is not known how many of these vehicles are currently operating in the UK. In calculating the potential gains from relaxing the current volume restrictions in conventional semi-trailers, it has not been possible to differentiate the benefits of increasing the cubic capacity of the vehicle from the benefits of double-decking. 5. Analysis of the Potential Use of Double-deck / High-cube Semi-trailers As indicated earlier, no official statistics are collected on the cubic volume of loads carried by, or the volumetric capacity of, goods vehicles. On the basis of the weight data collected by the CSRGT, however, it is possible to make inferences about the degree of volume-constraint by comparing the lading of 32½ tonne and 38 tonne articulated vehicles. 2 Both 32½ and 38 tonne articulated vehicles are subject to the same size limits. Most of the vehicles plated at these gross tonnages are of similar dimensions and, apart from differences in the number of axles, are usually indistinguishable on the road. 32½ tonne artics are used mainly for the movement of less dense products that exhaust the available cubic capacity or deck space in the trailer before the weight limit is reached. Two assumptions underpin the analysis reported in this paper: 1. Operators will choose to use a 32½ tonne arctic if volume is likely to be the limiting factor. After all, a lorry plated at 32½ tonnes offers a 10 per cent saving over a 38 tonner in terms of standing and running costs [Motor Transport, 1996]. 2. Operators of 32½ tonne and 38 tonne articulated lorries will make equal effort to maximise vehicle utilisation. One would expect that, in the absence of volume / deck space constraints, 32½ tonne and 38 tonne artics would have a similar average lading factor (by weight). In practice, the CSRGT reveals that the lading factor of 32½ tonne artics, at 49 per cent, is much lower than that of 38 tonne artics (70 per cent). There are two possible reasons for this discrepancy. First, 32½ tonne artics might be more heavily involved in multiple drop trips, with more of the driver s time taken up off-loading and collecting consignments. 2 The division of lorries in the CSRGT into weight classes prevents a direct comparison of articulated vehicles plated at precisely of 32½ tonnes and 38 tonnes. Published data from this survey divides artics into two weight categories: above and below 33 tonnes. Reference to 32½ tonne articulated vehicles in this paper, in fact, relates to vehicles with gross weights between 3.5 and 32.5 tonnes. The vast majority of these vehicles, however, are plated at 32.5 tonnes and less than 3 per cent of total road tonne-kilometres are carried in articulated lorries with plated weights of less than 25 tonnes. Similarly, references to 38 tonne vehicles relate to articulated lorries in the tonne category, though only a very small proportion of 9

11 Average payload weight would then be more tightly constrained by the available delivery time than in the case of 38 tonne operations which generally take the form of long distance, single-drop trunk hauls. Unpublished data from the CSRGT, however, suggests that this is cannot explain such a wide discrepancy, as the average number of drops per trip for 32½ tonners is only marginally higher that than of 38 tonne lorries at 1.6 and 1.1 respectively. 3 The second reason is that 32½ tonne artics are carrying a preponderance of loads that are volume- or deck area-constrained rather than weight-constrained. Firms can transport low density consignments more cheaply on 32½ tonne artics given their lower standing and operating costs. This is likely to be the main explanation of the lower (weight-based) lading factor on 32½ tonne artics. If operators were able to increase the volume, or the deck area, or both, of semi-trailers hauled by 32½ tonne artics then the lading of such vehicles would improve. Given that the average payload on a 32½ tonne artic represents only 49 per cent of the legal maximum, there is considerable scope for improved loading. If it were possible, through greater use of double-deck / high-cube semi-trailers, to improve the lading of 32½ tonne artics to match that achieved by 38 tonne artics, significant reductions in transport costs and lorry traffic could be achieved. Figure 2: Tonne kilometres carried and lading factors of 32½ and 38 tonne artics, 1980 to Thousand tonne kilometers Lading Factor Year T-km 32 T-km 38 lading 32 lading 38 Source: CSRGT and [Newton,85] them are plated at less than 38 tonnes. Altogether, vehicles plated at exactly 32½ tonnes or 38 tonnes account for 84 per cent of the total articulated lorry fleet [Department of Transport, 1996c]. 3 The CSRGT groups trips with 5 or more drops. In averaging the number of drops per trip, these trips were counted as having 5 drops. Only 12% of 32½ tonner and 5% of 38 tonner trips fall into this category. 10

12 This argument can be supported by two further pieces of evidence. Figure 2 shows the impact that the introduction of 38 tonne artics has had on tonne-kilometres and lading trends for 38 and 32½ tonne artics over the period 1980 to While the lading of both vehicle weight classes dropped after the introduction of 38 tonne artics in 1983, it can be seen that the lading of 32½ tonners fell further. This is consistent with operators involved in the transport of dense goods employing 38 tonne units, and operators who are constrained by factors other than weight continuing to use 32½ tonne units. This would have the effect of depressing the average lading of 32½ tonners. The second piece of evidence comes from a survey carried out by the Transport Research Laboratory of 248 operators in November 1991 [Newton and Frith, 1993]. The operators were asked if they intended to upgrade or replace their existing three or four axle artics at or under 32½ tonnes with heavier vehicles, as and when Britain s maximum lorry weight derogation expired. This study found that 74 per cent of the 32½ tonne four axle articulated lorry fleet would not be upgraded to the 35 tonne limit and that 67 per cent of the 32½ tonne fleet would be unaffected by the 38 tonnes limit. It also discovered that very few operators of artics below 32½ tonnes had plans to replace them with heavier vehicles whatever the changes to maximum weights. The most likely explanation of these survey results is that the utilisation of 32½ artics was limited by volume or deck area, rather than weight. Indeed, today, only 1.3 per cent of artics have a gross weight between 33 tonnes and 37 tonnes [Department of Transport, 1996c]. Table 2: Tonne-kilometres and Vehicle Lading Factors for Different Commodities, Commodity Classification: Million Tonne-kilometres Lading Factors (%) Rigids 32½t 38t total 32½t 38t all Agricultural products 2, ,024 12, Beverages ,835 5, Other foodstuffs 2,927 4,304 12,090 19, Wood, timber & cork ,554 3, Fertiliser ,282 1, Sand, gravel & clay 2, ,898 4, Other crude minerals 6, ,664 8, Ores ,016 1, Crude materials ,422 1, Coal & coke ,120 2, Petrol & products 1, ,200 5, Chemicals ,034 7, Cements ,156 2, Other building materials 2, ,667 7, Iron & steel products ,667 7, Other metal products , Machinery & transport equip. 1,994 1,868 3,580 7, Miscellaneous manufacture 3,201 2,175 7,895 13, Miscellaneous transactions 8,390 4,256 15,117 27, Total/Average 37,539 15,937 90, , Source: Published and unpublished data from CSRGT. 11

13 Relaxing the volume and/or deck area constraints would only be beneficial for firms moving lower density products. To establish which commodity groups might derive the greatest benefit from the increased use of double-deck / high-cube vehicles, an analysis was made of unpublished, disaggregated data from the CSRGT (Table 2). This identified the commodity classes which make heavy use of 32½ tonne artics and whose average lading on these vehicles is significantly below their average lading on 38 tonners. If, for each commodity, by making greater use of double-deck / high-cube trailers, operators were to achieve the same lading on 32½ tonne artics that already is achieved on 38 tonne artics, it would be possible, other things being equal, to cut the annual distance travelled by articulated lorries and reduce the number of lorries on the road. An attempt was made to estimate the magnitude of these savings. The method of calculation is illustrated by the following worked example: Let us assume that, for a specified commodity group, the average lading factor for 32½ tonne artics is 50 per cent and for 38 tonne artics 70 per cent. The efficiency increase that would accrue from raising the average lading of 32½ tonners to that of 38 tonners can be calculated by dividing the lading of the former by the latter (50% / 70% = 71%). This shows that, following such an improvement in lading, the 32½ tonne fleet could be reduced to 71 per cent of its former capacity while handling the same volume of freight movement. This represents a reduction of 29 per cent in the total capacity of the 32½ tonne fleet to carry tonne-kilometres on loaded trips. Dividing this reduction in tonne-km capacity by the original average payload weight indicates the corresponding reduction in loaded vehicle-kilometres. The number of loaded vehicle-kilometres will also decrease by 29 per cent. It is likely that, other things being equal, the amount of empty running would decline by a similar proportion. This assumes, quite reasonably, that the ratio of loaded outbound journeys to empty back hauls remains the same. As empty running represents roughly 30 per cent of the total distance travelled by 32½ tonne artics (the CSRGT does not differentiate empty running in relation to the commodity carried on the outward leg of the journey), a 29 per cent reduction in empty vehicle-kilometres would reduce the total distance travelled by 8 per cent. Adding the savings in loaded and empty vehicle-kilometres yields a total reduction in 32½ tonne artic traffic of 37 per cent for this particular commodity group. Assuming that the annual distance travelled by lorries in this weight class remained constant, this would translate into a 37 per cent reduction in the numbers of 32½ tonne artics transporting this type of product. This calculation was performed for each of the commodity groups to estimate the potential savings at individual commodity level, making allowance for the associated reduction in empty running (Table 3). The magnitude of these potential savings varied enormously depending on two factors: a) the disparity in the average lading of 32½ and 38 tonners; b) the relative proportions of tonne-kilometres carried by 32½ and 38 tonners. 12

14 Table 3: Potential Savings by Commodity from Improved Lading of 32½ tonne Artics Commodity class 32½ tonne artic TKm as Difference in mean lading of Potential Savings in Vehicle Kilometres (%) % of 38 tonne 32½ and 38 tonne 32½ tonne artics All artics artic TKm artics (%) Miscellaneous manufactured Other metal products Crude materials Miscellaneous transactions Other foodstuffs Chemicals Wood, timber & cork Other building materials Agricultural products Machinery & transport equip Beverages Iron & steel products Petrol & products Fertiliser Sand, gravel & clay Other crude minerals Ores Coal & coke Cements Average (weighted) signifies less than 1 per cent In Table 3 commodities have been ranked in terms of the percentage reductions in total articulated vehicle kilometres that might be achieved by raising the average lading of 32½ tonne artics to that of 38 tonners. Several commodity groups at the bottom of this table would derive little or no benefit for several reasons: a) very little of these commodities is carried on 32½ tonne artics; b) the average lading of 32½ tonne and 38 tonne artics is very similar; c) the types of vehicle used by the commodities (for example, tankers or tippers) are unsuited to double-decking or enlargement. These commodities, comprising beverages, iron & steel products, petrol and related products, fertiliser, sand, gravel and clay, other crude minerals, ores, coal, coke and cements have been excluded from further consideration. To assess the overall effect of this measure on articulated traffic, it is necessary to take account of the relative contribution of different commodity groups to the total movement of freight by road. This is indicated in Table 4. This table also ranks the targeted commodity groups in terms of the potential reductions in lorry numbers and vehicle kilometres. Aggregating these figures suggests that total vehicle requirements could be reduced by approximately 6,500 and total articulated vehicle kilometres by 525 million. 13

15 Table 4: Potential Contribution of Targeted Commodities to Total Savings.(1995 data) Million Vehicle kilometres Vehicle Population Percentage Reduction Miscellaneous transactions 181 2, Miscellaneous manufacture 120 1, Other foodstuffs 105 1, Chemicals Agricultural products Other building materials Machinery and transport equipment Other metal products Wood, timber and cork Crude materials The commodities offering the greatest potential savings to the economy were miscellaneous manufactured goods, other foodstuffs and, most significantly, the residual category of products which the CSRGT describes as miscellaneous transactions (Table 4). Other commodities which make significant use of 32½ tonne artics and that offer potential savings are: chemicals; other building materials; other metal products; agricultural products; wood, timber and cork; crude materials; machinery and transport equipment. Analysis of the growth of freight traffic since 1980 indicates that the three commodities which have most to gain from an increase in the lading of 32½ tonne artics have been increasing their share of total road freight movement (Figure 3). Freight in the miscellaneous transactions category in particular has grown very rapidly. If this trend continues the potential benefits of improved vehicle space utilisation will increase. 50 Figure 3: Low Density Commodities' Share of Total Road Tonne-kilometres, 1986 to 1995 Percentage share of total tonne kilometres Year Source: CSRGT Miscellaneous transactions, miscellaneous manufacture and other foodstuff It was estimated that the overall effect of raising the average lading of 32½ tonners to that of 38 tonners would be to reduce the total annual distance travelled by the 32½ tonne artic fleet by 525 million vehicle- 14

16 kilometres (20%), equivalent to roughly 5% of total articulated lorry traffic. Assuming that the average annual distance travelled by each 32½ tonner remained constant, it would be possible to take around 6500 lorries off the road. It was noted that, even if the lading of 32½ tonne units transporting freight in the miscellaneous transactions category reached the level attained by 38 tonne units, it would still fall well short of that achieved by the movement of every other commodity type in 38 tonne lorries. Articulated vehicles, in both the 32½ tonne and 38 tonne weight classes, have a poor average lading factor for this commodity, of only around 50 per cent. This suggests that some operators may be incurring unnecessary cost by running 38 tonne artics where 32½ tonne artics would suffice. It also indicates that, in the case of this product group, there may be considerable potential for enlarging / double-decking 38 tonne vehicles as well as 32½ tonners. If this were to raise the lading factor to the average for all artics (which is 66 per cent), then a further reduction of 390 million vehicle-kilometres could be achieved. This would remove around 4000 articulated lorries from the road. These potential savings are more speculative. Much of the freight classified as miscellaneous transactions takes the form of parcels traffic, much of which is delivered on an express basis. Load factors in this sector are likely to be tightly constrained by delivery schedules and not simply by the cubic capacity / deck space on the vehicle. The calculation, nevertheless, illustrates that the benefits of expanding cubic capacity / double-decking need not be confined to the 32½ tonne articulated lorry fleet. The potential reductions in lorry traffic and vehicle numbers are summarised in Table 5. Together, the two measures outlined above could reduce the total volume of articulated lorry traffic by 915 million vehiclekilometres per annum (almost 9 per cent of all articulated vehicle kilometres) and cut the fleet requirement by 10,500. This could yield large economic and environmental benefits. In the following two sections an attempt is made to assess the benefits that might accrue from improved cube utilisation of 32½ tonne artics. As the effects of double-decking / enlarging 38 tonners are highly speculative at this stage, they will be excluded from the assessment. Table 5: Potential Savings from the Improved Space Utilisation of Articulated Vehicles (1995 data) Raising average lading factor of: Reduction in Vehicle Kilometres (million) Reduction in Vehicle Numbers 32½ tonners to that of 38 tonners all artics carrying miscellaneous transactions as 38 tonners to the average for all 38 tonne artics Total

17 6. Economic Benefits from Increased Use of Double-deck / High-cube Trailers The full cost of operating a 32½ tonne artic (including running and standing charges) is currently around 1.05 per mile [Motor Transport, 1996]. The estimated reduction in vehicle-kilometres from raising the average lading factor of 32½ tonne vehicles to that of 38 tonners would therefore save approximately 340 million gross per annum. This accrues not only from improved utilisation of the vehicle assets but from improvements in driver productivity expressed on a tonne-km per hour basis. Firms operating these vehicles on routes requiring a sea crossing could make further savings in ferry / tunnel charges. To calculate the net savings, it would be necessary to make allowance for any extra costs associated with owning and operating double-deck / high-cube vehicles: 1. Higher capital cost: Capital cost comparisons are complicated by the wide variety of vehicle specifications and construction methods. Table 6 illustrates the differences in purchase cost and carrying capacity between various types of purpose-built double-deck trailer and their conventional counterparts. These costs were quoted by a trailer manufacturer for the one-off purchase of a single trailer. In the case of curtain-siders, the insertion of a fixed double-deck adds approximately 9-10,000 to the purchase price, increasing it by 50 per cent. The addition of a movable double-deck to a curtain-sider or the double-decking of a box van approximately doubles the price. Where a firm purchases a large fleet of double-deck trailers built to a standard design the premium paid for double-decking is usually much smaller and may even be completely eliminated. 2. Cost of converting conventional semi-trailers: Converting a conventional trailer can be cheaper than a one-off purchase of a purpose-built unit. One firm has reported spending roughly on the installation of a rotating double-deck in a standard curtain-sider. Purpose-built vehicles, however, have superior design and construction and can, as a result, be operated more cheaply than converted trailers. 3. Any extra costs incurred in operating these vehicles: Operating costs can be higher for several reasons. First, the installation of an upper deck can increase the tare weight of the vehicle and, as a result, increase fuel consumption. The use of light steel frames in the latest generation of purpose-built curtainsiders has, however, largely eliminated this weight penalty, as shown Table 6. Second, high-cube vehicles are generally higher and thus experience a stronger drag effect. This also tends to impair fuel efficiency, though the fuel penalty can be minimised by improved aerodynamic profiling. Third, those operators using trailers with smaller road wheels will experience a small reduction in the life of tyres and break linings. 4. Any extra costs incurred in maintaining these vehicles: Some of the firms operating double-deck units report that their maintenance costs have been slightly higher. This was partly the result of structural weaknesses in earlier generations of double-deck trailers and partly because of damage done to the support pillars during loading and unloading. Most of the earlier teething problems have now been overcome, partly as result of improved staff training, experience and supervision in the use of doubledeck trailers. 16

18 5. Capital expenditure on any modifications that may be required to premises: Some firms have altered reception bays to facilitate the loading and unloading of double-deck / high-cube trailers. In most cases, however, this has involved modest expenditure. In the case of curtain-siders, conventional fork-lift trucks can service both lower and upper decks, obviating the need for special platforms. It is not possible, on the basis of available data, to quantify all of these extra costs or to compare double-deck / high-cube and conventional trailers on a full life basis. It appears, however, that in the case of curtainsided vehicles, the cost penalties are quite marginal. Even for the other categories of double-deck / highcube vehicle, the additional costs seem low when set against the increases in carrying capacity. A high-cube semi-trailer, for example, typically increases the useful volume by 40 per cent, while the insertion of an upper deck effectively doubles the available deck area. Table 6: Comparison of Conventional and Purpose-Built Double-deck Semi-trailers Cost Weight Pallets Cages Thousand Kg 1000x1200mm 686x813mm Number of Axles: Conventional Boxvan ,300 8, Conventional Curtain Sider ,400 7, DD Boxvan (small wheels) ,000 10, DD Boxvan stub axles ,500 11, DD Curtain Sider ,600 7, Movable DD Curtain Sider ,700 8, A double-deck semi-trailer can have a volume capacity of up to 105 cubic meters. The only other vehicle combination with a similar cubic capacity is a close-couple draw bar combination. Interestingly, the capital cost of a draw-bar combination is much the same as a double-deck boxvan semi-trailer. The double-deck semi-trailer has the advantage that it is easier to manoeuvre and thus likely to be more popular with drivers. As a single trailer, however, it does not offer the same operational flexibility as a drawbar trailer combination which can be split into two separate units. A double-deck curtain-sider offers the lowest capital cost per pallet, with only a very slight loss of payload weight when set against a conventional semi-trailer (Table 6). In practice, however, hauliers will only have an incentive to use a double-deck trailer if rates are related to the size / weight of load carried. At present, general haulage rates are typically determined on a distance basis for individual trips and not related to vehicle loading. By consolidating loads in trailers with greater cubic capacity / deck space and reducing the number of trips required to deliver a fixed quantity, a haulier would make fewer trips and potentially lose revenue as a result. The nature of the charging regime is unlikely to constrain the growth of double-deck / high-cube semi-trailers on dedicated contract and own account operations. 17

19 7. Environmental Benefits from Increased Use of Double-deck / High-cube Trailers The reduction in the distance travelled by 32½ tonne articulated lorries would translate into a reduction in exhaust emissions. Emissions would be unlikely to decrease in direct proportion to the decline in vehicle kilometres as high-cube vehicles tend to have a higher rate of fuel consumption. Their fuel efficiency, however, is only marginally lower and much of the consolidation would be achieved by the double-decking of standard semi-trailers which would not be subject to additional drag. Any reduction in fuel efficiency resulting from an increase in trailer dimensions could be minimised by improvements in aerodynamic profiling. It could also be offset by the displacement from the fleet, by the new generation of double-deck / high-cube vehicles, of older lorries with above average rates of fuel consumption. If the consolidation of loads in double-deck / high-cube 32½ tonne artics were to reduce the distance travelled by these vehicles by 525 million kilometres per annum (Table 5), fuel consumption would be reduced by approximately 197 million litres per annum (worth 107 million, including tax, at 1995 prices). This would significantly reduce the emissions of a broad range of pollutants (Table 7). Table 7: Estimated Annual Reduction in Emissions emissions: g/km emitted Total reductions (tonnes) Carbon Dioxide 1, ,225 Sulphur Dioxide Black Smoke ,014 NMVOC ,872 NOx ,213 CO ,974 PM The estimates presented in Table 7 are based on the results of recent research on motor vehicle exhaust emissions by Solway et al. (1996). This expresses some emissions as a function of fuel consumed and others in relation to distance travelled. To simplify interpretation, these emissions are presented in Table 7 on a distance-related basis. In the case of particulate matter under ten microns in diameter (PM10), which has become a major cause for concern because of its carcinogenic properties, the precise reductions are difficult to calculate as they are dependent on the age profile of the articulated lorry fleet and the distribution of traffic among different road types. The estimated reduction in emission levels is based on the assumption that any reductions in the 32½ tonne articulated fleet would be of vehicles manufactured before Articulated lorries constructed after this date were subject to more stringent emission controls and are thus less environmentally damaging. The estimates have been compiled using data from traffic censuses, which show that for every ten kilometres covered, the average artic travels five on motorways, one on rural dual carriageways, three on rural single carriageways and one on urban roads [Department of Transport, 1996c]. 18

20 The environmental benefits would not be confined to the decrease in exhaust emissions. Noise irritation, road-side vibration and accident levels would also be reduced. As in the case of air pollution, these environmental impacts would not decline in direct proportion to the reduction in vehicle kilometres. They would be likely to decline by a greater margin as a result of the substitution of older, more environmentallydamaging equipment by new trailers conforming to the most recent standards. The consolidation of loads in double-deck / high-cube vehicles would also help to alleviate congestion, though its net effect on traffic levels would be very small. If the average lading factor of 32½ tonners converged on that of 38 tonners, overall road traffic levels would only be reduced by around 0.12 per cent. This reflects the fact that 32½ tonne articulated lorries account for only 0.6 per cent of all road traffic. Even if these lorries are given a passenger car unit rating of 2, their share of road traffic only rises to 1.12 per cent. Traffic congestion is predominantly a car-based problem. One of the less welcome effects would be the greater visual intrusion of high-cube vehicles. There is no denying that these vehicles can appear larger, more unsightly and more threatening, especially on urban roads. Operators could help to reduce their visual impact by modifying their livery and resisting the temptation to use the extra surface area for larger advertisements. It should be emphasised too that much of the consolidation would be achieved by double-decking standard semi-trailers which would be no bigger than the vast majority of HGVs currently on the road. A major assumption underlies all these estimates of environmental benefits: that an increase in transport efficiency, and hence a reduction in transport unit costs, would not cause firms to increase their demand for freight transport. It is possible that firms would respond to the resulting transport cost reduction by restructuring their logistical systems and/or sourcing and distributing products over longer distances. If this were to happen, much of the environmental benefit could be eroded. The central issue is whether this measure would be likely to promote a move to more transport-intensive production and distribution or whether it would simply help to reduce the environmental impact of logistical restructuring that would take place anyway. The experience of one major firm in the food and drink sector supports the latter view. A high level strategic decision was made to centralise the distribution operation, motivated primarily by sales, inventory and asset-utilisation considerations. An effort was then made to find ways of maximising transport efficiency within the new system. The use of double-deck trailers was examined as a possible option and subsequently adopted. In other companies, however, the opportunities created by double-deck / high-cube vehicles might exert a stronger influence on system design and trading patterns. This is an issue which will require further research. It is also possible that increasing the cubic capacity / deck space in lorries would result in the diversion of some freight traffic from rail to road or make it more difficult for rail to increase its share of the freight market. Such a modal shift away from rail would have an adverse effect on the environment. It is unlikely, however, that the proposed improvement to the cube utilisation of 32½ tonners would have much effect on the modal split, for two reasons. First, the main beneficiaries of this measure would be low density, manufactured goods which are not suited to movement by rail given the tight height restrictions on railway 19