ROAD INTERSECTIONS AND SAFETY ROAD INFRASTRUCTURE

To provide knowledge on the design of different types of road intersections (both at-grade intersections and interchanges) and to provide concepts for the preparation of active and passive safety measures that contribute to increasing the overall functionality of road infrastructures.

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The course includes classroom lectures and works conducted in groups of 2 students (with the exception of the limitations imposed by the COVID -19 emergency).

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The work consists of the analysis of two road intersections (standard and roundabout) and their adaptation.

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Students who, after presenting the appropriate documentation (DR n.1598 of 2/5/2018), have obtained recognition as a working student, sports student, student in difficulty and student with disabilities, if it is not possible for them to carry out the work in a group with other students of the course, will carry out a personalized work, the modalities of which will be agreed with the teacher.

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There are no prerequisites. However, it is strongly recommended to have taken the exam of "Road Infrastructure Project" or at least to have acquired the frequencies.

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Class participation is strongly encouraged as this is consistent with the proposed educational model, which is designed to encourage gradual learning, active student participation in the classroom, and dialogue between teachers and students. Since the group works will take place in the classroom, attendance is strongly recommended.

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The didactic material is represented by the reference texts already provided. Additional material required for the teaching activity will be made available on the website: www.stradelandia.it

1. INTRODUCTION

Road safety and intersections. Road intersections as key elements of road networks. Types of road intersections: at grade junctions and interchanges. Choice of the type of intersection. Project parameters.

2. STANDARD INTERSECTIONS

Main types of standard intersections. Definitions and criteria for choosing specialized lanes. Design criteria of the specialized lanes: Central accumulation lane. Entrance lane. Central entry lane. Exit lane. Edge lines. Traffic islands: dividing islands, directional islands, refuge islands. Sight distances.

3. ROUNDABOUTS

Feasibility and planning: objectives. Analysis of the context. Site-specific conditions. Check availability of required land. Comparison with other design alternatives. Modern roundabouts: Italian legislation. Main design rule: control of lane deflection. Procedural sequence for planoaltimetric design of modern roundabouts: arrangement of legs. Mutual inclination of the converging arms. Diameter of the roundabout crown. Width of the circulatory roadway. Central island. Dividing islands. Entrance. Entrance curves. Exit. Exit curves. Visibility criteria. Visibility at intersection (visibility to the left). Visibility for stopping. Cross-section of the circulatory roadway. Mini-roundabouts: advantages, disadvantages and applications. Design criteria. Large diameter roundabouts: weaving sections design. Geometric design. Interchanges: Diamond-shaped intersection. Half cloverleaf intersection. Roundabout interchange. Roundabout-Target : Two-level roundabout with bypass lanes for right turners. Turbo roundabouts: classification of turbo roundabouts. Characteristic elements and design criteria. Safety: conflicts and conflict points. Accidents at roundabouts: Types and causal factors. Operational performance: traffic data collection. Roundabout performance analysis methods (HCM Edition 6 (2016) method, deterministic software, microsimulation software). Special cases and alternative schemes: By-pass lanes for right turners. Flower roundabouts. Roundabouts with double bends. Roundabouts with underground road crossing. Roundabouts crossed by railroad tracks. Mobile roundabouts.

4. INTERCHANGES

Main interchanges schemes. Overpasses. Interconnection ramps. Coordination factors of the ramps. Planimetric conformation of the ramps: Exit section. Intermediate section of deceleration. Section with constant curvature. Intermediate section of acceleration. Entry section. Final connection section. Altimetric conformation of the ramps. Weaving sections.

5. ROAD SIGNAGE FOR SAFETY OF INTERSECTIONS

Role of signage in road safety. Road marks. Road signs. Complementary signs. Signage for standard intersections and roundabouts.

6. DEVICES FOR PASSIVE SAFETY OF ROADS

Types of retaining devices. Safety barriers. Vehicle-barrier collision. Types of road barriers. Installation conditions of metal barriers and concrete barriers. Passive protection systems for dangerous points. Crash cushions. Simple and special terminals. Transitions. Retaining devices for two-wheeled vehicles.

7. ROADS ILLUMINATION FOR THE SAFETY FROM ROADS AND TUNNELS.
Safety at night on sections and junctions. Parameters affecting night vision. Values of lighting parameters. Study areas. Reference, design and operational lighting categories. Lamps and luminaires. Presentation of photometric characteristics. Arrangement of light points on the elements of the road network (curves and intersections). Project of a street lighting system. Daylight illumination of road tunnels. Lighting of long tunnels and short tunnels. Design of an artificial lighting system. Night lighting of road tunnels. Lighting solutions and requirements: Luminance of walls and roadway. Uniformity of luminance. Limitation of glare. Limitation of flicker (flicker effect). Light sources. Types of lighting systems. Partialization of lamps ignitions. Emergency lighting. Maintenance of the lighting system.

1. S. Canale. N. Distefano. S. Leonardi. G. Pappalardo. “Progettare le intersezioni. Tecniche per la progettazione e la verifica delle intersezioni stradali in ambito urbano ed extraurbano secondo il D.M. 19/4/2006”. EPC Editore. II Edizione. Settembre 2011.
2. S. Leonardi. N. Distefano. “ROTATORIE STRADALI. Manuale di pianificazione, progettazione e gestione”. EPC Editore. Marzo 2021.
3. S. Canale, N. Distefano, S. Leonardi. “Progettare la sicurezza stradale. Criteri e verifiche di sicurezza per la progettazione e l’adeguamento degli elementi delle infrastrutture viarie: intersezioni, tronchi, sovrastrutture, gallerie, opere idrauliche, barriere di sicurezza, illuminazione, segnaletica ed interventi di traffic calming”. EPC Libri. Maggio 2009.