Credible Variable Speed Limits for Improving Road Safety: A Case Study Based on Italian Two-Lane Rural Roads

Stefano Coropulis (), Paolo Intini, Nicola Introcaso and Vittorio Ranieri
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Stefano Coropulis: Department of Civil, Environmental, Land, Building Engineering and Chemistry, Politecnico di Bari, 70125 Bari, Italy
Paolo Intini: Department of Innovation Engineering, University of Salento, 73100 Lecce, Italy
Nicola Introcaso: Department of Civil, Environmental, Land, Building Engineering and Chemistry, Politecnico di Bari, 70125 Bari, Italy
Vittorio Ranieri: Department of Civil, Environmental, Land, Building Engineering and Chemistry, Politecnico di Bari, 70125 Bari, Italy

Sustainability, 2025, vol. 17, issue 11, 1-24

Abstract: In an ever-changing driving environment where vehicles are becoming smarter, more autonomous, and more connected, a paradigmatic change in signals for drivers might be required. This need is correlated with road safety (social sustainability). There are several factors affecting road safety, and one of these, especially important on rural roads, is speed. One way to actively influence drivers’ speed is to intervene with regard to speed limit signs by providing credible and effective limits. This goal can be pursued by working on variable speed limits that align with the boundary conditions of the installation site. In this research, an analysis was conducted on the rural road network within the Metropolitan City of Bari (Italy) that involved collecting the speeds on each of the investigated two-way, two-lane rural roads of the network. In addition to the speeds, all the most relevant geometric details of the roads were considered, together with environmental factors like rainfall. A generalized linear model was developed to correlate the operating speed limits and other variables together with information about rainfall, which degrades tire–pavement friction and thus, road safety. After the development of this model, safety performance functions, depending on the amount of rain or number of days of rain, were calculated with the intent of predicting crash frequency, starting with the operative speed and rain conditions. Operative speed, speed limit, percentage of non-compliant drivers, traffic level, and site length were found to be associated with all typologies and locations of crashes investigated.

Keywords: variable speed limit; operative speed; statistical models; road safety; rainfall (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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