Design and Implementation of a VSL System

Severe atmospheric and road surface conditions on rural highways create a variety of transportation hazards. Variable Speed Limit (VSL) systems can mitigate the dangers caused by these conditions by displaying prudent maximum speed limits that reflect the prevailing atmospheric and road surface conditions. This paper discusses the design and implementation of a fuzzy rulebased system (FRBS) that serves as the computational engine of a prototype VSL system designed for use on rural highways. The design of the FRBS is based on Bart Kosco’s Standard Additive Model. This model defines a representation of fuzzy systems that is powerful but also conceptually and computationally simple. The FRBS was used in preliminary tests of a prototype VSL system that utilized information transmitted by Road Weather Information Stations located along the I-40 corridor in rural Northern Arizona. This corridor is subject to various types of inclement weather conditions as it passes through a variety of geographic locations that range from desert to mountainous terrain.