There is also a close link between transportation options and material handling capabilities. At the harvest site, large open-topped chip van trailers can be loaded evenly by a conveyor, overhead hopper or front-end bucket loader. Closed trailers and box trucks, as well as trailers that cannot be approached from the side due to terrain or road conditions, must be loaded from the back. Depending on the particle size of the material and ejection range of processing equipment, it may be difficult to fill long compartments uniformly to maximize payload. Similarly, grapple loaders must have sufficient room to maneuver to efficiently load roundwood or compacted bundles onto long trailers. Unloading is discussed in more detail later in this chapter, but similar constraints apply to unloading biomass. Self-unloading configurations, including walking floor (Figure 14.9), side dump, end dump and belly dump trucks and trailers, carry smaller payloads than long, possum belly semi-trailers, but may be required if the end user does not have a hydraulic truck dump system on site. For

roundwood, self-loading log trucks equipped with a hydraulic grapple arm may be required if the log landing does not have a loader or forwarder on site.

Regulations and handling constraints apply broadly to all biomass supply chains but the forest sector is unique in the extent to which transportation logistics are dictated by harvest site characteristics. Plantations and native forests located on flat topography close to end users and accessed over high-speed, wide, paved roads with high GVW are obviously ideal for minimizing transportation costs. However, forested sites are frequently accessed over gravel or native soil low-standard forest roads that are steep, narrow and winding with limited turn-out locations for passing and turning around. In many cases, forest roads were designed for stinger steered log trucks and are inaccessible to the long, low clearance, high-volume tractor-semi-trailer combinations that maximize transportation efficiency for woody biomass. Road improvements can widen curves, flatten rough roads and reduce steep grades, but can rarely be justified by biomass extraction objectives alone and may be limited by regulation or forest management objectives. Recent innovations in stinger steering and rear axle modifications that allow a tighter turn radius than traditional fifth wheel semi­trailers with fixed axles have improved access to difficult sites by large semi-trailers. Such trailers are commercially available but cost more than conventional equipment. Short chip van tractor-semi-trailer configurations are also used to haul woody biomass on low-standard forest roads. Under especially challenging road conditions, shorter, higher clearance, and more maneuverable box trucks, dump trucks, roll-off bins, or tractor-trailers are an option. However, the smaller payloads carried by these vehicles typically translate to higher per unit transportation costs, which are intensified by long on-highway travel distances. In addition, if biomass has received some field drying before processing, smaller truck configurations tend to reach maximum volume before they reach maximum GVW. This is suboptimal from a logistics standpoint because it further reduces payload and increases per unit costs.