Rise of the trailer drone

Since its invention, the semi-trailer has been trailing behind the truck – not just in the sense of being towed, but especially with view to technological progress. Could the advent of autonomous driving turn the system upside down?

With the next IAA Commercial Vehicle Show just half a year away, autonomous driving is quickly positioning itself to become the event’s most hotly debated topic. No other technological megatrend has proven more polarising within the transport community, and no other transport industry issue has found such resonance among the general public since we last convened in Hanover, northern Germany.

Despite the issue’s growing impact on society at large, however, the discussion has rarely touched on the role of the trailer – even though the removal of the driver’s cab could make for a unique opportunity to challenge the very notion of modern truck-trailer design and lead to a dramatic, yet still widely overlooked, paradigm shift: the rise of the trailer drone.



Without a typical driver’s cab, the pulling unit would be reduced to providing basic propulsion and supporting a portion of the load. So why not let the trailer itself take over that function? With a self-propelled and self-supporting load compartment, a truck – in the traditional sense – would no longer be required.



Since trailer drones would have to assume the basic functions of a truck, the question of who would manufacture them arises: Are trailer manufacturers up for the task, or might truck manufacturers take the lead? Perhaps this question is best answered after taking a closer look at the trailer drone’s potential design.



Unlike contemporary trucks, trailer drones would be much simpler to design and manufacture. The backbone of a drone may be related to the kind of skeletal frame used for the loading of demountable bodies, such as ISO containers, swap bodies or swap containers. Given that drones can theoretically operate 24/7, the use of demountable bodies would be key to ensuring maximum uptime.



The skeletal frame would be designed along the lines of a railcar, with independent front and rear bogies that are counter-steered. With an advanced active steering system, this would ensure easy control of the drone by artificial intelligence and/or by tele-operation. Furthermore, this steering setup could theoretically allow for a new overall maximum length of 19.5m (64’) – which is still within turning-circle requirements specified under EU Directive 96/53/EC.



Depending on the desired axle configuration and axle load requirement, the front and rear bogies could be either inboard (large overhang) or outboard (no overhang). Furthermore, an additional central bogie could be fitted in order to achieve higher gross weights.



At the front of a drone would likely be an aerodynamic nose cone, connected directly to the skeletal frame. This particular feature is what distinguishes a trailer drone from an autonomous truck, with the advantage that no gap exists between the nose cone and the demountable body. As such, aerodynamic efficiency would not be compromised by the need to facilitate turning clearance.



The nose cone may houses the core components of the systems required to enable autonomous driving, as well as remote control. Since a drone is a semi-trailer at heart, it would be fitted with a sophisticated electronic braking system for trailers (T-EBS). Furthermore, a so-called drive control module (DCM) could be fitted to command the T-EBS, as is the case with modern trucks via CAN bus. The DCM would control all inputs to powertrain, steering, and braking systems, as is the case of a driver inside a truck cabin, albeit via instruction from an on-board computer and/or a remote operator.



Since the invention of the internal combustion engine (ICE), the “powertrain” has been the most complicated aspect of a heavy vehicle. However, this may no longer be the case with the feasibility of battery-electric heavy vehicles (BEHV), such as the Tesla Semi. Furthermore, battery-electric powertrains are widely considered to be more suitable choice for autonomous vehicles. This is partially due to their fewer parts, minimal downtime, packaging flexibility, and responsive control.



While a diesel engine could be incorporated into a trailer drone without much difficulty, a battery-electric powertrain should make it more feasible in the longterm – even though a battery-electric powertrain would suffer some general drawbacks, such as higher cost, higher weight and longer ‘refuelling’ times. And yet, the higher weight and cost of a battery pack would likely be offset by the lower weight and cost of a trailer drone chassis. What’s more, as already indicated by Tesla, long battery recharging times could be offset via simple battery swapping.



Given that the barriers to entry for a battery-electric vehicle manufacturer are considerably lower than they are for an ICE vehicle manufacturer, what could prevent an ambitious and forward-thinking trailer manufacturer from developing a trailer drone – especially since they can readily acquire most of the required autonomous driving technology and battery-electric hardware from the plethora of eager suppliers joining the field?



The question becomes even more pressing given that it is rather unlikely that truck manufacturers will embrace the trailer drone. Over the years, trucks and semi-trailers developed independently of each other, despite the valiant attempts to integrate them – for example with the Mercedes-Benz EXT-92 – and despite the considerable potential of integration. It is expected that the status quo will prevail upon the advent of autonomous driving, with truck OEM merely ‘updating’ the existing offering to potentially create truck drones that may or may not be able to be integrated with trailer drones.



Being independent of the semi-trailer, truck drones would provide the flexibility to tow various kinds of semi-trailers for various kinds of loads, much like current trucks do. As a product of the truck manufacturing industry, a truck drone would benefit from decades of technical expertise, considerable R&D resources and vast sales/aftersales networks. In fact, there is little doubt it would initially have the upper hand.



Nevertheless, the truck drone may not enjoy a strong market position for long. An entirely new breed of heavy vehicle that is fully integrated, light and simple to design, as well as cheap to manufacture and operate, the trailer drone does make economic sense – even more so since it could also serve as a basis for a new generation of autonomous buses and coaches. As such, it is not unlikely the ‘balance of power’ could one day shift in favour of the trailer drone.



With every step towards autonomous driving, the long, mutually beneficial partnership truck and trailer manufacturers have forged over the past 120 years will therefore come under more pressure. Could it turn trusted partners into fierce competitors? Only trailer manufacturers can answer this question.