Is reducing the speed of heavy goods vehicles from 90 to 80 km/h the best way to reduce their GHGS emissions? Let’s examine the impacts of this proposal…

A drop of 3.75% in diesel…

If we reduce the speed of heavy goods vehicles from 90 to 80 km/h, we only reduce GHG production by 1.25%. But the cost of transport increases by 12.5%, in the same ratio as the reduction in speed.

It’s true, reducing speed reduces fuel consumption. If we reduce the cruising speed of heavy goods vehicles running on diesel from 90 to 80km/h (-12.5%), we spend less energy to overcome air resistance (25% reduction because air resistance air increases as the square of the cruising speed). That said, the average efficiency of a heavy-duty engine is only 15%. In other words, if the engine consumes 30l/h, only 4.5l/h is used to propel the vehicle. The rest go into heat.So reducing air resistance by going from 90 to 80km/h saves 25%x15%, or 3.75% of the diesel needed for propulsion. Not far from the 4% announced by the Shift Project.

… but a 12.5% ​​increase in truck and driver time!

But conversely, the truck and its driver will drive for 12.5% ​​more time to provide the same service. You will therefore have to pay 12.5% ​​more truck and driver time. This will certainly reduce unemployment, but it will also require 12.5% ​​more trucks  to deliver the same quantities under the same working conditions. Note that the construction and recovery at the end of its life of an additional truck produces at least 20% (100T) of CO2 in addition to the 500T emitted during the life of the vehicle. The carbon footprint of this initiative is reduced accordingly (-20%*12.5% ​​or -2.5%). So we will reduce GHG emissions by 1.25% (3.75%-2.5%) if we reduce the speed from 90 to 80km/h. Always good to take but the expected saving of 4% is reduced to 1.25% at best.

What is the optimal speed for trucks?

The question therefore arises of the optimal speed of movement of heavy goods vehicles to remain economically and environmentally efficient. Reducing speed is desirable to reduce fuel consumption and improve safety, but unfortunately goes against the very purpose of transportation. If this were not the case, it would undoubtedly be in our interest to reduce the speed even further until we find an optimum for the carbon footprint between slowing down freight and building vehicles or driving faster and producing fewer trucks to reach a optimal consumption.Note that manufacturers have currently adjusted the engines to have optimal performance at 86km/h, or practically 90km/h. Obviously, we could also reduce the distances to travel, to have the best of both ecological and economic worlds, by putting cities in the countryside as Alphonse Allais said. The last trend in the Netherlands is to plant vertically in the cities. Have the countryside or at least the vegetable garden at home.

Fast, filled, efficient, safe and non-polluting trucks

More realistically, the solution to the ecological and energy equation is not to have trucks driving slowly. It’s about having fast, full, efficient, safe and non-polluting heavy goods vehicles. Their speed, efficiency and filling rate should make it possible to reduce the number and kilometers traveled. Their safety and absence of pollution will guarantee their effectiveness.These are the areas being explored: faster, streamlined, autonomous, environmentally friendly and efficient trucks. This is the path that the manufacturers have taken. In addition to this, to increase the vehicle occupancy rate, it is necessary to review the physical distribution network and implement a concentration of flows to minimize the last mile.

To be convinced of this, let’s imagine a construction customer to deliver concrete every 2 hours to a construction site 90km away. At 90 km/h it will be able to make the round trip in 2 hours, thus fulfilling its contract with a single truck. If we limit the speed to 45 km/h, it will be necessary, to offer the same service, to use 2 trucks leaving alternately every 2 hours and commuting. The number of trucks on the road depends on their speed. The higher the speed the less vehicles on the road.

Jean-Patrice Netter

Founding President
DIAGMA