From 1 September, the first longer truck cabs meeting an official new EU derogation will be allowed to drive on Continental roads. The 80-90cm of cab length they permit could offer superior aerodynamics, enhanced driver vision and improved safety.
"European truck cabs have been shaped like bricks for the past 50 years. That’s set to change,” states James Nix, freight director at Transport & Environment, which campaigned for the introduction of the legislation.
Vehicle makers who choose the extra cab length, which is not mandatory, will have to sign up early to the EU’s coming raft of rules for cars, vans and trucks in the General Safety Regulation (2019/2144). That includes a number of measures including Direct Vision (widely enforced from 2028), cyclist detection and warning systems, driver drowsiness and attention warnings, TPMS and reversing cameras (all widely enforced from 2024). It remains uncertain, however, whether the UK will adopt the regulation once it leaves the EU.
But if it does not, UK operators may be at a disadvantage, says TRL head of biomechanics Phil Martin, as adopting aerodynamic cabs will reduce vehicle drag, and hence improve fuel consumption. Martin was involved in conducting cost-benefit research that evaluated a range of vehicle safety features, work that supported development of the regulation.
He says: “The length derogation is all about improving the aerodynamic design of the cab. The regulation ensures that this has the additional effect of improving driver comfort and the safety of vulnerable road users [VRUs].”
Two particular exterior design changes are regulated: rake, how much the cab leans back from the front edge in a vertical plane, and taper, which is the degree to which the vehicle’s sides merge toward a point in front. In case of a collision with a VRU, increasing the rake reduces the risk of head injury, as the vehicle is more likely to hit lower body features such as hips and torso, absorbing some of the impact energy. The increase in taper angle may also further deflect the VRU laterally away from the wheels, reducing run-over risk.
Because of increased rake and taper, VRUs will be located farther from the driver, reducing the forward blind spot.
In particular, the design envelope requires a rake of at least 3° from 1m to 2m high, and 20° of taper from the maximum width of the vehicle. Both of these changes have to be within 200mm of the front of the vehicle, according to Martin. That might allow a long-haul cab to be extended by up to about a metre at ground level, but overall length still depends on turning circle maximums.