Research Article Modelling the Operating Speed in Segments of Two-Lane Highways from Probe Vehicle Data: A Stochastic Frontier Approach António Lobo , Marco Amorim, Carlos Rodrigues, and António Couto Research Centre for Territory, Transports and Environment, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal Correspondence should be addressed to Ant´ onio Lobo; lobo@fe.up.pt Received 15 November 2017; Revised 5 March 2018; Accepted 13 March 2018; Published 18 April 2018 Academic Editor: Abdelaziz Bensrhair Copyright © 2018 Ant´ onio Lobo et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Most of the existing operating speed statistical models are applicable to individual design elements, particularly horizontal curves and tangents. A segment approach to operating speed has rarely been followed, with a few exceptions mainly related to the performance assessment of urban and freeway corridors, or design consistency studies using speed profles built from successive design elements. Tis study introduces a new model to predict operating speeds in segments of two-lane highways. Te maximum operating speed is given by a stochastic frontier function of the average daily trafc and road geometrics; the asymmetric disturbance accounts for the diversity in drivers’ behaviour and vehicle characteristics, allowing estimating any percentile speed. Te model was calibrated using probe vehicle data from noncongested roads. Te accuracy of the average daily trafc in representing the actual driving conditions was further validated using simultaneous speed-trafc measurements. Te new model aims to assist practitioners in the evaluation of design consistency from a macroscopic perspective since the early stages of road planning and design, as well as to support the defnition of speed limits at new or existing infrastructures. 1. Introduction Increasing eforts to understand and predict operating speeds in roadway facilities have been developed across the past decades, following the tendency of researchers and practi- tioners to use the operating speed as an instrument to defne road geometrics and promote design consistency. Te great majority of the existing models are focused on the purely geometric efects on driving speeds, exploring the relations between geometric parameters and the speeds practiced under free-fow conditions in individual design elements, especially in horizontal curves or tangents. Such models are commonly known as spot speed models, of which the Trans- portation Research Circular E-C151 [1] provides a comprehen- sive review. Te operating speed in a road segment, defned as a continuous sequence of design elements composing a stretch of road, has been much less studied, despite the relevance that segment speed estimations based on roadway characteristics may present to the evaluation of road design and operations. Te use of segment speed prediction models since the early stages of road design allows practitioners to verify, for each design iteration, if the diferences between the selected design speed and the expected operating speed lie within acceptable limits. A sensitivity analysis on such diferences could shed light on the variables most infuencing design consistency, thus providing an insight into the most efective actions to control it in the following iterations of the design process, with the ultimate goal of obtaining a satisfactory fnal solu- tion. Tis procedure is in line with the suggestions made by Fitzpatrick et al. [2] regarding the use of alignment indices to evaluate design consistency from a macroscopic perspective. Nevertheless, to improve safety performance, Fitzpatrick et al. [2] advocate that such analysis should be complemented by a conventional speed profle approach based on the evalua- tion of speed reductions between successive design elements. Hindawi Journal of Advanced Transportation Volume 2018, Article ID 3540785, 10 pages https://doi.org/10.1155/2018/3540785