Phase 2 results

[Publication Date: February 2020]

In the second phase of the project (July 2018 - September 2019), experimental tests to dynamically reduce speed limits for traffic and environmental purposes by displaying the limits on variable message sign positioned along the motorway carriageway continued with different management methods.

The results confirm the positive impacts of the application of the dynamic speed limits already highlighted during phase 1 of the project, both in terms of improving traffic fluidity in days with a high number of vehicular transits and in terms of improving air quality.

The application of reduced speed limits for the optimisation of motorway capacity benefited from the implementation of a semi-automatic traffic management system, which made it possible to optimise the dynamic management of speed limits with positive effects on the reduction of congested traffic situations and consequently on pollutant emissions. 

The application of reduced speed limits for environmental purposes, on the other hand, has seen lower benefits than those highlighted during phase 1, due to a lower speed reduction by light vehicles during the experiments. This was caused by the need, for regulatory reasons, to display the recommended speed signal instead of the speed limit signal used during phase 1. In any case, the results obtained in terms of reduction of nitrogen oxide concentrations at the motorway edge are consistent with the speed reduction recorded during the experimental sessions. In particular, the experimental data collected during phase 2 showed decreases of about 7% for nitrogen monoxide and about 2-3% for nitrogen dioxide with an average speed reduction for light vehicles of about 5 km/h, compared with reductions of 10% for both species in phase 1 with an average speed reduction for light vehicles of about 14 km/h.

Phase 2 test results report (in Italian)