Although construction logistics activities are the source of significant environmental nuisances, they are often overlooked. Limited knowledge is available about the true vehicle-kilometres (vkm) associated with the large number of vehicles in the sector. Furthermore, current studies are insufficiently robust to determine the share of construction logistics in total freight transport and its environmental effects. Countries like Belgium and the Netherlands have organized simultaneous holiday periods for the construction sector. This period is driven by the sector itself to avoid delays (within teams and between related companies). The scheme is well-respected despite the regional aspect, as 88% of the construction sector is adhering to it. Consequently, the comparison of the freight transport activities – be it traffic counts or GPS data – could be made between the organized holiday period and a reference period. This paper proposes a macro-level analysis to determine (1) the share, (2) the fleet composition and (3) the environmental impact of construction logistics within Heavy Goods Vehicle (HGV) traffic. This is done using On-Board Unit (GPS) data, covering almost all road vehicles with a gross weight of >3,5t on the entire territory of Belgium. This analysis is conducted over reference periods of 4 years (2016-2019). This allows to quantify the influence of the HGV construction logistics fleet on Belgian traffic, for which an external costs analysis (air pollution, accidents, climate change, congestion, loss of habitat, infrastructure, noise and well-to-tank costs) is conducted. Results show that these vehicles, largely construction-related, represent approximately 17.58% of total HGV traffic, or 14.86% of total daily active HGVs. Overall, these transports generate €1.45mio daily external costs, a share which represents 15.33% of total HGV external costs in Belgium. These figures should be considered lower bounds.