Intelligent Speed Adaptation and driving speed: Effects of different system HMI functionalities Ioanna K. Spyropoulou a,⇑ , Matthew G. Karlaftis b , Nick Reed c a School of Rural and Surveying Engineering, Laboratory of Transportation Engineering, 9 Heroon Politechniou Street, 15780 Zografou, Athens, Greece. b School of Civil Engineering, Department of Transportation Planning and Engineering, National Technical University of Athens, 5 Iroon Polytechniou Street, 15773 Athens, Greece c Transport Research Laboratory, Wokingham RG40 3GA, United Kingdom article info Article history: Received 26 September 2012 Received in revised form 27 February 2014 Accepted 28 February 2014 Keywords: Speed Intelligent Speed Adaptation Human machine interface Simulator Intelligent transport systems Driver behaviour abstract In this paper we study driver behaviour changes when driving vehicles equipped with Intelligent Speed Adaptation (ISA) systems. The primary tool used is a driving simulator. Three different ISA human machine interface functionalities are investigated: informative, warning, and intervening. Data were extracted from the simulator along with question- naires completed by drivers following each drive. Possible impacts of system functional- ities on driver behaviour are studied through appropriate metrics including driving speed, speed deviation, frequency and magnitude of speeding and the empirical cumula- tive distribution function of speeding. Perceived impacts on drivers are investigated to identify driver attitudes towards the systems as well as possible relations between antic- ipated and measured behaviour. The study indicates that use of ISA systems, in general, results in the adoption of vehicle speeds that are likely to improve road safety. However, we also found that drivers may misuse ISA systems, potentially resulting in negative road safety effects. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Speeding comprises one of the major causes of road accidents (ETSC, 1995), contributing to increased accident and sever- ity rates (Allsop, 1990; Evans, 2004; Kallberg, 1998; Kloeden, Ponte, & McLean, 2001; Nilsson, 1982). Conventional road safety measures such as speed enforcement and variable speed limits have been shown to have an effect, albeit transitory, both in terms of duration and location (Abdel-Aty, Dilmore, & Dhindsa, 2006; Goldenbeld & van Schagen, 2005; Hauer, Ahlin, & Bowser, 1982; Lee, Hellinga, & Saccomanno, 2006). Intelligent Speed Adaptation (ISA) systems involve the modulation of vehicle speed within prescribed (fixed or variable) limits. They are expected to reduce speeding offences and hence improve road safety (Carsten & Tate, 2005; Spyropoulou, Golias, Karlaftis, Penttinen, & Vaa, 2008). However, driver attitudes towards ISA systems are a contributing factor in the extent to which speeding may be reduced. This in turn depends on several ele- ments including system capabilities, driver and trip characteristics. The main functional modalities of an ISA system in terms of their human machine interface (HMI) are informative, warn- ing and intervening (ETSC, 2005, 2006). The system operates by constantly monitoring driving speed and comparing it to a threshold speed. Specific actions are triggered by the system either throughout the drive or if the monitored speed exceeds http://dx.doi.org/10.1016/j.trf.2014.02.008 1369-8478/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +30 2107722778; fax: +30 2107722629. E-mail address: iospyrop@central.ntua.gr (I.K. Spyropoulou). Transportation Research Part F 24 (2014) 39–49 Contents lists available at ScienceDirect Transportation Research Part F journal homepage: www.elsevier.com/locate/trf