In 2012 the German Federal Government started a five-year field trial with longer trucks. One scientific project focused on empirical data of the logistic and transport processes as well as the modelling of future mileage and market shares of longer trucks. Based on predefined scenarios, potential areas of application and accessible routes for longer trucks were determined using a likelihood approach with particular attention to the different definitions of a longer truck suitable road network. In a second step empirical data covering logistic characteristics collected from participating carriers and forwarders were integrated into a sophisticated transport model in order to estimate transport demand effects and emissions of air pollutants as well as greenhouse gases stemming from longer trucks in normal business operations. The analyses of the traffic demand modelling for the scenarios shows for the reference years 2014 and 2030 that due to logistical constraints and requirements (generally) only a small part of all German heavy good vehicle trips (about 3.0 to 3.2 %) and even a smaller part of all rail and inland waterway transport performance (1.8 and 2.9 %) can be considered as potentially shiftable to longer trucks.