Effects of geometric design on freeway capacity: Impacts of truck lane restrictions

This paper presents a framework for estimating analytical expressions for the capacity reductions caused by a subset of vehicles forced to slow down at horizontal/vertical curves on multilane freeways. In each lane the underperforming stream is described in terms of its desired speed distribution (either discrete or continuous), and it is explicitly modeled as a stochastic process that disturbs light vehicles as per Newell's kinematic wave theory of moving bottlenecks. The model is applied for estimating the impact of truck lane restrictions. It is found that system capacity is maximized either (i) when each truck type uses a different lane or (ii) when they share the same lane, depending on the relative proportion of heavy trucks. Moreover, this application sheds some light to the puzzling empirical result in several places around the world, where time and time again it is observed that the operational improvements of truck lane restrictions are small or negligible.Freeway capacity Truck special lanes Kinematic wave theory Moving bottlenecks