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The construction of the third lane of the Venice-Trieste motorway

copertina 3a corsia
  • Infrastructure
  • Structure
  • Environment
  • Hydraulics
  • Mobility
  • Systems
  • Safety

Improving the efficiency of the service through safety and innovation.

The final design to widen the A4 Turin-Trieste motorway from two to three lanes was developed in two different projects. The first concerned the section in Veneto, between San Donà di Piave and the Alvisopoli junction for an overall distance of 33 km+500 m. The second project concerned the part in Friuli Venezia Giulia, in the Quarto d’Altino-Sistiana section, and between Gonars and Villesse, for a distance of 15 km+862 m.

In Veneto, the project included the upgrade of the Cessalto, Santo Stino di Livenza and Portogruaro by-pass, the variants of the interfering ordinary road network and some new roads. The planned works included significant structural works, particularly those concerning the crossing of the River Livenza.




In Friuli, the Palmanova intersection, a motorway junction close to the built-up area of Palmanova which allows the interconnection between the A4 and A23 motorways, was significant. The three routes, Udine, Venice and Trieste, are symmetrically connected with a three-pointed star configuration. This is a singular point where ramps and structures, which have been adequately sized and checked from the transport and safety points of view, are concentrated.

Special attention was paid to the study of the environmental and landscape integration of the work, with the intention of creating infrastructure that becomes an integral part of the landscape, also transforming it, as far as possible, into a planted corridor where part of the structures can reinforce the environmental characterisation of the area. For this purpose, the project suggested large longitudinal planted structures, in both the central reservation and along the lateral structures (the line of trees along the path).

The retarding basins/treatment of first flush waters were relevant in the motorway green system both because of their extension and the potential ecological role they could have when the installations are established. In addition, soundproofing, the recovery of excavated material, and specific treatment for first flush waters were planned.

The effects socially and on the project area can be summarised as follows: resolution of extensive flooding problems in the areas near to the A4; improvement of accessibility of the infrastructure; improvement of the ‘permeability of the work’ from the hydraulic and secondary connections points of view; improvement of the safety conditions in the operation of the infrastructures; improvement of the safety conditions during construction; green works and environmental mitigation respecting the Kyoto protocol.


The San Donà di Piave-Alvisopoli section in Veneto

The overall length of this section of the project is about 33.5 km and set out the updating of the junctions of Cessalto and Portogruaro and the transfer of the toll booth of San Stino di Livenza. An Environmental Impact Study and an Environmental Effects Study were drafted for this section. The design used a multi-disciplinary approach typical of system engineering to indicate the best technical solutions, using multiple criteria analysis. The infrastructure concerns the area of seven municipalities in Veneto and three provinces; their involvement was necessary so that solutions where several bodies had given their opinion could be shared. During design, technical discussions were started to the advantage of the area concerned by the work, which enabled the rationalisation of crossings of the River Livenza, the many existing canals and the optimisation of the reclamation network drainage systems through the planning of a 14-km gutter channel parallel to the A4. The hydraulic work also acts as a body of water to protect the area and, in relation to the morphology of the area, flood prevention after heavy rain. Likewise, the project also set out the updating of significant structures such as 12 bridges and viaducts, 18 flyovers, 20 underpasses, with the prospect of a future widening of the motorway section to four lanes.

The project has a system of water disposal from the roadway with a purification process through a first treatment plant (oil spill tank) which intercepts the pollutants if there is an incident – an automated procedure is planned for this purpose managed by the concessionaire’s control centre; a lamination or lagooning area, to ensure the hydraulic constancy of the system through the modulation of flow.

The other arrangements include: a technological communication network (fibre optics), traditional electricity and telephone networks, the remote monitoring of the gutter and a system of diversified plants for video surveillance and the automatic traffic control system. All these technological networks enabled a reduction in the maintenance and operating costs, an improvement in users’ safety through the detection of dangerous conditions and optimised management of emergency situations.


The Gonars-Villesse section in Friuli

The project concerned the construction of the third lane of the A4 motorway between the junctions of Gonars (province of Udine) and Villesse (province of Gorizia) for an overall distance of about 16 km. The section involved in the work included the Palmanova junction, where there is the intersection between the A4 and the A23 ‘Alpe-Adria’ motorway, considered one of the critical points of the whole Veneto/Friuli motorway network in terms of congestion and accident rate. The extension of the road section enabled the optimisation of the geometric conformation of the intersection and vehicle traffic flow conditions through a careful transport study.

From the environmental point of view, the construction of new green areas along the motorway route was planned to compensate for the estimated increase in the CO2 emissions, in accordance with the indications of the Kyoto Protocol. In addition, the plant for the collection and treatment of first flush waters, based on phyto-treatment technologies, was designed. The project also set out the updating of all the structural works, a viaduct, 7 flyovers and 7 underpasses, which were sized with the prospect of a future widening of the motorway section to four lanes.

Analysis of accident rate

NET Engineering developed an analysis of the accident rate in both sections that set out the statistical analysis road collisions in the previous three years and the cinematic reconstruction of the various types of incident so that the risk factors linked to the infrastructure could be indicated and adequate minimisation measures chosen. The application of an innovative traffic simulation model, based on a statistical description of the behaviour of vehicles incorporated in a set of similar features (MESOSIMULATION), enabled the impact of the construction sites on circulation to be assessed and their space-time positioning to be organised better to ensure the highest possible safety levels and optimisation of vehicle traffic flow conditions.

Dialogue with stakeholders

As already mentioned, during the planning stage a technical discussion was initiated with local authorities and services. In particular, the relationship and dialogue with the Consorzi di Bonifica has greatly influenced the planning phase. In fact, these are entities that have been waiting for the construction of the work for some time to start a common process aimed at solving the numerous critical issues of the water network close to the road infrastructure, which in turn led to situations of flooding, creating inconvenience to the territory.

The solution studied and implemented envisages a gutter channel approximately 14 km long, capable of filling, north of the A4, the excess volumes of water during meteoric events, and redistributing them correctly in the channels south of the A4, through a system of sluice gates and overflows capable of suitably regulating excess flow rates.

This optimal solution was identified only thanks to a constant and fruitful dialogue with the institution concerned.

The direct involvement of stakeholders right from the design phase is a procedure that NET Engineering constantly applies, certain of the benefits that the sharing of choices in the design phase generates in the subsequent steps of approval and implementation of the projects.

The feasibility study and the design of the Turin-Venice line
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