Last week’s cover story of Transport Engineer compared platooning of heavy goods vehicles with higher capacity vehicles.
At first glance, these two concepts seem similar: connect two or more heavy vehicle units to make them more efficient…
A platoon uses various sensors plus wireless communication between vehicle units and a sophisticated software control system to ensure that each vehicle follows the one in front, automatically, with a small spacing – typically 6m (20 ft) or less. The drivers of the trailing vehicles don’t drive when the platoon is operating. However, they are still needed in the cab, to control the vehicle when it is not in the platoon (eg at either end of the journey). Click here for more details about truck platooning.
For higher capacity vehicles, the vehicle units are physically connected using hardware – for example a ‘dolly’ (a short 2-axle trailer with drawbar that supports the front end of a semitrailer). There is one prime mover (‘tractor’) and one driver.
If you take 2 tractor-semitrailer vehicles and put them in a platoon with current technology, the spacing between vehicles is about 6m and fuel consumption of the combination drops by 3-5% due to the reduction in aerodynamic drag. If you could make the second vehicle follow very closely behind the first (which has difficult control and safety implications), you could save about 7-10% of fuel.
If, instead, the second tractor unit is replaced by a dolly (see Fig. 1), this is a so-called ‘A-double’ combination, which has the same freight capacity as the 2-vehicle platoon. However, that is where the similarity ends:
- the A-double has only one tractor unit instead of two pulling the same two trailers;
- it has one engine instead of two: burning fuel, generating emissions, and requiring maintenance;
- the gap between the vehicle units is about 1.8m, giving better aerodynamic performance;
- there is one less axle on the A-double, reducing the rolling resistance and fuel consumption further;
- the A-double weighs about 6 tonnes less than the 2-vehicle platoon, reducing the effects on the infrastructure (damage to roads and bridges);
- it is about 7m shorter than the 2-vehicle platoon, making it easier for cars to pass;
- the fuel consumption of the A-double is approximately 20-25% less than the two original vehicles;
- there is only one driver, so operating costs are significantly reduced as well.
Importantly, the physical connection between the vehicle units in the A-double is simple, robust and uses mature technology. It does not rely on sophisticated safety-critical control software to ensure that the necessary vehicle spacing can be maintained safely at highway speeds.
Experience from operations of high capacity vehicles in Australia, Canada, South Africa, Nordic countries and the Netherlands have shown that when these vehicles are operated within a thoughtful legislative framework, they are consistently a lot safer than conventional lorries.
So my question is this: Why is there so much hype about platooning, when simply connecting the vehicle units with standard coupling technologies gives safer, more fuel-efficient and significantly lower-cost freight operations; with better environmental performance and less damage to the infrastructure?…
The answer, of course, is political. Platoons are sexy. High capacity vehicles are big and scary (though smaller and lighter than the equivalent platoons, as seen in the figure). Politicians prefer political expedience to listening to the evidence and making decisions that benefit the planet.