Does power curb energy efficiency? Evidence from two decades of European truck tests

In the last two decades the European truck industry has made remarkable progress in energy efficiency, but this higher efficiency has failed to materialize in lower consumption per unit of load and distance (Tkm). One possible explanation is rebound effects due to average travelling speed and power enhancements. We present here an original set of data covering twenty years of truck tests of 114 heavy-duty vehicles from 1999 to 2018. We compared fuel intensity (L/100 km) assessed under standard conditions (performance tests) with actual consumption recorded on road tests, concluding that journeying fuel intensity improved much less in normal driving conditions than in performance tests. We regressed journeying fuel intensity on a range of relevant variables, using a diverse set of models to cover different ways of relating data variables to each other. We found that average speed, though it increased, was not a significant factor in determining journeying fuel consumption. Instead, changes in rated power, maximum weight, absorbed power and first order efficiency were significant variables, and rebound effects associated with increased vehicle power were consistently evident and ranged from 6.130% to 20.21%, depending on the statistical model employed.