Abstract Nearly 99% of Colombian roads have two lanes. In order to improve their level of service (LOS), they have been turned into multilane roads through the doubling of existing highways without technical criteria to justify such transformation, and without considering more appropriate alternatives such as auxiliary lanes. Due to Colombia’s mountainous topography and the high weight/power ratio of the vehicles in circulation, research on auxiliary lanes has been carried out to clarify their applicability. However, operational evaluation procedures such as the Highway Capacity Manual (HCM) may not be representative for the infrastructure and vehicles in Colombia. The hypothesis is that the operational benefits of climbing lanes on two-lane roads with Colombian infrastructures and trucks are higher than the HCM estimate. The objective is to carry out an operational evaluation of the effect of auxiliary lanes on traffic in 84.000 scenarios, and to determine threshold values of operational indicators in order to provide guidance for a better design of this kind of infrastructure. The operational analysis was performed on a virtual road with an auxiliary lane with Colombian trucks and a variety of road geometry and traffic features. Traffic operations were simulated with TWOPAS, part of the Interactive Highway Safety Design Model (IHSDM), for which the computational program PEMAT was created. The results demonstrate the benefits of auxiliary lanes on the improvement of Percent Time Spent Following (PTSF) and Average Travel Speed (ATS), and define criteria for geometric design.