Automatic control of variable message signs in the interurban Scottish highway network Albert Messmer a , Markos Papageorgiou b, *, Neil Mackenzie c a Ingenieurbu Èro A. Messmer, Sommerstr. 12, 81543 Mu Ènchen, Germany b Department of Production and Engineering Management, Dynamic Systems and Simulation Laboratory, Technical University of Crete, University Campus, GR-73100 Chania, Greece c National Roads Directorate, The Scottish Oce Development Department, Victoria Quay, Edinburgh EH66QQ, UK Received 1 July 1996; received in revised form 31 July 1998; accepted 31 July 1998 Abstract The paper presents the design, implementation, and evaluation work performed by a European con- sortium for the development of a Variable Message Sign (VMS) information and guidance system in the interurban Scottish highway network. The control strategy employed is based on simple automatic control concepts with both feedback and feedforward terms subject to user-optimum constraints. Feedforward terms are employed for the prediction of travel times and delays along long-distance interurban highway links. Simulation studies demonstrate the potential improvements achievable with these kinds of control measures and control strategies. The implementation concepts and ®eld evaluation results are outlined. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Variable message signs; Driver information; Route guidance; Scottish highway network; Automatic control; Feedback; ATIS; Re-routing 1. Introduction Interurban highway networks typically oer to the network users a multiplicity of possible routes connecting each origin-destination pair in the network. Even commuters, usually opti- mizing their proper path on the basis of their daily experience, may encounter diculties in view of changing demands, road works, changing weather conditions, exceptional events (e.g. holi- days, sport events, fairs), and incidents which perturb trac ¯ow conditions in the network in a non-predictable way. As a consequence of the lack of real-time information on the current trac 1369-8478/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S0968-090X(98)00014-X TRANSPORTATION RESEARCH PART C Transportation Research Part C 6 (1998) 173±187 * Corresponding author. Tel.: 00 30 821 69324; fax: 00 30 821 69568; e-mail: markos@dssl.tuc.gr