Vehicle size and weight restrictions
As discussed above, many loads ‘weigh-out’ before all the vehicle space is filled or ‘cube-out’ before the vehicle reaches its maximum gross weight. Legal restrictions on vehicle weights and dimensions, therefore, result in either weight or volume-carrying capacity being under-utilized (McKinnon, 2005). As weight limits have been raised by a greater margin than size limits in recent decades, over a period when the average density of freight has been declining, a higher proportion of loads are now volume constrained than weight constrained. This is clearly illustrated in the UK, where just over twice as many of the loads carried by trucks with gross weights of over 38 tonnes are volume constrained as weight constrained (Figure 9.4).
Increasing the maximum size of trucks can therefore allow companies to consolidate loads, achieving greater vehicle fill and cutting truck-kms. It is possible to gain extra cubic capacity vertically or horizontally. In some countries, most notably the UK where bridge and tunnel clearances over the road network are relatively high (mainly to accommodate double-deck buses), it is possible to increase vehicle height and insert a double-deck to permit the carriage of two layers of pallets.1 Britain actually has no legal limit on vehicle height though, because of infrastructural constraints, five metres is generally considered the maximum. Companies carrying low-density products have the most to gain from the use of double-decks, and for this reason they are now extensively used by major retailers and parcel carriers in the UK (McKinnon and Campbell, 1997). One large UK retailer has demonstrated the benefits of double-decking by comparing operating parameters for deliveries using a double-deck vehicle and two single-deck vehicles with similar capacity. Unit delivery costs, vehicle-kms and CO2 emissions were all around 48 per cent lower (DfT, 2005b).
Across much of the European mainland a four-metre height limit applies, tightly restricting, but not eliminating, opportunities for doubledecking. In other European countries, such as Sweden, Finland and the Netherlands, companies have gained extra cube ‘horizontally’ by lengthening the vehicle. Often this increase in length and axle numbers has been accompanied by a relaxation of the maximum weight limit. Currently, within the EU, Council Directive 96/53/EC permits a maximum vehicle length of 18.75 m for a draw bar-trailer combination and 16.5 m for semitrailer articulated vehicles. Trailers and semi-trailers that comply with these regulations can be combined to greater overall lengths of up to 25.25 m in the so-called European modular system. All EU member states have the right to operate these longer vehicles for domestic use (ie as long as they do not cross international borders or distort international competition in the transport sector). Until recently no EU country had introduced longer and heavier vehicles (LHVs) as a result of the 96/53/EC directive, though the use of LHVs in Sweden and Finland pre-dated their entry to the EU (McKinnon, 2008). In 2007, following a successful on-theroad trial, the Dutch government decided to permit 25.25-metre-long trucks up to a maximum gross weight of 50 tonnes (since raised to 60 tonnes). Studies of the environmental and economic impact of LHVs have also been conducted in Germany (UBA, 2007), Belgium (Debauche and Decock, 2007), Sweden (Vierth et al, 2008) and the UK (Knight et al, 2008). Partly in the light of this evidence, the governments of both countries have refused to legalize 25.25-metre vehicles, though Britain is considering increasing the maximum length of articulated vehicles with a single trailer from 16.5 to 18.75 metres. A recent EU-funded study concluded that LHVs could be widely introduced in Europe ‘without harming European society as a whole’, though it recognized the need for several «counter-measures» to minimize the negative impact on alternative modes, allay safety concerns and prepare the road infrastructure (Transport and Mobility Leuven et al, 2008). Rail freight organizations (eg UIC et al, 2007) and environmental groups (eg European Federation of Transport and the Environment, 2007) are vehemently opposed to the legalization of what they call ‘mega-trucks’.