ROAD INTERSECTIONS AND SAFETY ROAD INFRASTRUCTURE
Academic Year 2026/2027 - Teacher: SALVATORE LEONARDIExpected Learning Outcomes
The structure of the teaching and practical activities aims to achieve the following objectives, in accordance with the Dublin Descriptors:
- Knowledge and understanding: The student will acquire a solid theoretical and regulatory mastery regarding the geometric and functional design of road intersections, both at-grade and grade-separated. They will develop a profound awareness of the structural principles of active and passive safety, assimilating the rules for the safe design and adaptation of all types of road intersections, the lighting criteria for roads and tunnels, as well as the technical specifications for the installation of safety barriers, in order to maximize the overall functionality and safety of the infrastructures.
- Applying knowledge and understanding: Through the Scaffolded Project-Based Learning methodological approach, the student will translate the acquired notions into rigorous practical implementations. They will demonstrate the ability to perform the geometric layout of all the elements constituting the various types of road intersections, culminating in the fully autonomous development of a complete redevelopment project for an existing road node. This process will include the technical production of scaled plans, graphical visibility checks, and horizontal and vertical road sign plans, as well as the detailed drafting of the technical report explicitly detailing the various design choices and the criteria adopted for their implementation.
- Making judgements: The didactic approach of the flipped classroom and the unguided design phase will allow the student to develop strong critical thinking. They will be capable of identifying real-world road intersections that do not comply with safety standards, analyzing the existing conditions, and making reasoned choices for the reorganization of the original layout or its conversion into a different type of intersection. Such decision-making independence will be supported by the ability to formulate and interpret Origin/Destination matrices to impeccably justify the technical and scientific choices adopted.
- Communication skills: The student will refine their ability to argue and present their design solutions in a clear and professionally flawless manner, employing the specialized vocabulary of highway engineering. They will be able to draft technical-illustrative reports and graphic tables that meet professional industry standards, defending their choices during the oral examination. Furthermore, drafting the project in working groups will consolidate their aptitude for interpersonal communication, synergistic coordination, and strict adherence to set deadlines.
- Learning skills: The educational path, structured to proceed from the observation of practical cases to the formalization of abstract design rules, will equip the student with a flexible and permanent study method. The progressive transition from guided scaffolding exercises to autonomous applied work will guarantee the student the analytical maturity essential to independently tackle future regulatory updates, technological innovations, and complex professional challenges in the road infrastructure sector.
Course Structure
The official course website for all teaching activities related to the discipline is available at: www.stradelandia.it
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The course includes lectures and classroom exercises to be carried out as outlined in the course execution section..
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TEACHING METHODOLOGY
The course adopts a adapted version of the flipped classroom approach: instruction begins with the illustration of real and/or hypothetical design cases (e.g., road intersections or safety devices). Guided by the instructor, students observe and analyze these cases, compare alternative configurations, and evaluate their performance in terms of effectiveness and safety. Recurring patterns and criteria naturally emerge from this analysis, which are then progressively made explicit and formalized into design rules. In short: from the concrete to the theoretical, moving from practical examples to explicit design rules that can be applied to different contexts.
PRACTICAL EXERCISES
The course follows a progressive pedagogical framework based on Scaffolded Project-Based Learning, structured into two complementary methodological phases designed to guide students from the step-by-step acquisition of fundamental analytical-geometric techniques to the independent execution of a design project.
First Phase: Scaffolding Activity (Individual Guided Exercises)
The first phase serves as the scaffolding stage and aims to consolidate the calculation methods and geometric layout procedures required by current regulations for designing and checking the structural components of road intersections. Through individual classroom exercises conducted under the direct guidance of the teaching staff, students work on standardized case studies to develop the technical proficiency required for road junction design criteria.
Specifically, the scaffolding phase involves drafting the following technical documents:
- Design of a teardrop island in an at-grade linear intersection.
- Design of three-centered compound curves (including the determination of the corresponding swept paths) in an at-grade linear intersection.
- Design of a splitter island for a roundabout intersection.
- Verification of the deflection angle in a roundabout.
Second Phase: Independent Design Phase (Unguided Group Project)
The second phase represents the autonomous application of the skills acquired, where students work without the analytical and instructional scaffolding provided in the previous phase. Working in groups of up to 3 members, students select and propose an existing at-grade linear intersection. Subject to approval by the teaching staff, this intersection will serve as the case study for redevelopment.
The working group analyzes the existing conditions of the chosen junction and independently defines the geometric and functional upgrading strategy, providing a reasoned choice between reorganizing the initial linear layout or converting it into a roundabout intersection.
Upon completing the design phase, groups must submit the following project deliverables:
- Technical Report: containing the functional characterization of the junction, the formulation of an Origin-Destination (O-D) matrix justifying both the current and proposed conditions, the technical-scientific rationale behind the chosen layout, and the design and verification criteria adopted (explained individually).
- Existing Conditions Layout: general plan view at a 1:500 scale.
- Intersection Design Layout: proposed plan view at a 1:500 scale.
- Road Signage and Markings: horizontal markings and vertical signage plan at a 1:500 scale.
- Sight Distance Verifications: graphical representation of sight distance checks at a 1:1000 scale.
- Detailed Drawings (1:200 scale):
- For linear layouts: construction details of the teardrop island and development of the three-centered compound curves.
- For roundabout layouts: construction details of the splitter island and graphical/analytical verification of the deflection angles.
Submission Procedures and Deadlines
The submission of the full set of project deliverables (sent via email to the teaching staff) is a mandatory requirement for admission to the exam. It must take place at least seven days prior to the selected exam call, and in any case no later than the strict deadline set for the final exam call of the academic year (September 24, 2027).
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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.
Required Prerequisites
Attendance of Lessons
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.
Detailed Course Content
1. PASSIVE ROAD SAFETY DEVICES
Safety barriers. Classification of barriers according to functional and effectiveness criteria. Containment level. Impact severity level (ASI and THIV). Deformation level (dynamic deflection, working width, vehicle intrusion, working space). Classification of barriers based on material. Installation conditions for metal barriers. Installation conditions for concrete barriers. Selection criteria for safety barriers. Passive protection systems for specific hazard points. Crash cushions. End terminals. Transitions. Median opening barriers. Motorcycle safety devices.
2.
Road safety during nighttime driving. Lighting parameters. Lighting classes according to the UNI 11248 Standard. Study areas. Input lighting classes. Design lighting classes. Operating lighting classes. Adaptive road lighting. Lamps and luminaires. Representation of photometric characteristics. Design hypotheses to optimize system solutions. Arrangement of luminaires in curves. Arrangement of luminaires at pedestrian crossings. Arrangement of luminaires in intersection areas. Overview of lighting calculation for a road system.
Daytime lighting. Nighttime lighting. Luminance of walls and surfaces outside the carriageway. Luminance uniformity. Glare limitation. Light sources and system solutions. Overview of artificial lighting system design. Energy saving and system performance regulation. Standby/emergency lighting. Maintenance operations for the lighting system.
Geometric and functional classification of road intersections. Classification of intersections according to Ministerial Decree 19/04/2006. Choice of intersection type. Operational performance of intersections: evaluation tools and comparison of solutions. Intersection safety: conflicts and collision risk. Design choices deriving from the joint analysis of operational performance and safety requirements. Design parameters.
5. AT-GRADE LINEAR INTERSECTIONS
Introduction. Compositional elements of at-grade linear intersections: dedicated lanes and traffic islands. Dedicated lanes: admissibility, necessity, and minimum cross-sectional dimensions. Traffic islands. Procedural steps for the geometric and functional design of linear intersections. Teardrop island and widening of the intersection cross-section. Edge curves for right turns. Swept paths. Dedicated lanes. Central storage lane. Entry lane. Central merging lane. Exit lane. Pseudo-exit lane. Accessory traffic islands. Splitter islands. Directional islands (pseudo-triangular). Pedestrian refuge islands. Sight checks. Stopping sight distance. Maneuver sight distance. Sight triangles.
6. ROUNDABOUTS
Feasibility and planning: Objectives. Context analysis. Site-specific constraints. Verification of required space availability. Comparison with other design alternatives. Modern roundabouts: Italian legislation. Main design rule: control of trajectory deflection. Procedural steps for the horizontal and vertical design of modern roundabouts: Arrangement of legs. Reciprocal inclination of converging branches. Inscribed circle diameter. Circulatory roadway width. Central island. Splitter islands. Entries. Entry curves. Exits. Exit curves. Sight criteria. Intersection sight distance (sight to the left). Stopping sight distance. Cross-section of the circulatory roadway. Mini-roundabouts: Advantages, disadvantages, and fields of application. Design criteria. Large diameter roundabouts: Sizing of weaving sections. Geometric design. Grade-separated configurations: Diamond interchange. Partial cloverleaf interchange. Grade-separated roundabout. Target roundabout: double grade-separated roundabout with right-turn bypass lanes. Turbo roundabouts: Classification of turbo roundabouts. Characteristic elements and design criteria. Safety: Conflicts and conflict points. Roundabout accidents: types and causal factors. Operational performance: Traffic data acquisition. Methodologies for performance analysis of roundabout approaches (HCM Edition 6 (2016) method, deterministic software, micro-simulation software). Special cases and alternative schemes: Dedicated right-turn lanes. Flower roundabouts. Dog-bone roundabouts. Roundabouts with underpass road crossing. Roundabouts crossed by railway tracks. Temporary roundabouts.
7.
Introduction. Constituent elements of interchanges: ramps and overpass/underpass structures. Types of interchanges. Geometric design of modular elements in interchanges. Diverging section. Intermediate exit section. Constant radius section. Acceleration section. Merging section. Final connection section. Vertical design of ramps. Optimization of longitudinal profiles through vertical inflection points. Weaving zones.
Textbook Information
- N. Distefano, S. Leonardi.
"MANUALE DI PROGETTAZIONE PER LA SICUREZZA STRADALE. Strategie progettuali per la sicurezza degli elementi delle reti stradali urbane ed extraurbane: tronchi, intersezioni, percorsi pedonali e ciclabili, interventi di traffic calming, zone a traffico moderato, sovrastrutture, illuminazione, gallerie e dispositivi di ritenuta". EPC Editore. Novembre 2024. - N. Distefano, S. Leonardi. "INTERSEZIONI STRADALI. Manuale tecnico per il dimensionamento geometrico e la valutazione dei livelli di sicurezza delle diverse configurazioni progettuali in ambito urbano ed extraurbano". KDP Amazon - Marzo 2026.
- S. Leonardi. N. Distefano. “ROTATORIE STRADALI. Manuale di pianificazione, progettazione e gestione”. EPC Editore. Marzo 2021.
Course Planning
| Subjects | Text References | |
|---|---|---|
| 1 | 1. PASSIVE SAFETY DEVICES FOR ROADS: Restraint devices: reference standards, types and application areas. Safety barriers. Classification of barriers according to functional and effectiveness criteria. Containment level. Severity level (ASI and THIV). Deformation level (dynamic deflection, working width, intrusion, working space). Classification of barriers based on material. Installation conditions of metal barriers. Installation conditions of concrete barriers. Selection criteria for safety barriers. Passive protection systems for singular points. Impact attenuators. Terminals. Transitions. Barriers for closing gaps. Safety devices for motorcyclists. | Text 1 Chapter 9 (pages 335-372) |
| 2 | 2. ROAD LIGHTING FOR ROAD SAFETY: Road safety during night driving. Lighting parameters. Lighting categories according to the UNI 11248 Standard. Study zones. Input lighting categories. Design lighting categories. Operating lighting categories. Adaptive lighting of roads. Lamps and lighting fixtures. Representation of photometric characteristics. Design assumptions to optimize system solutions. Arrangement of light centers in curves. Arrangement of light centers at pedestrian crossings. Arrangement of light centers in intersection zones. Lighting calculation of a road system (brief notes). | Text 1 Chapter 7 (pages 267-298) |
| 3 | 3. ROAD LIGHTING FOR TUNNEL SAFETY: Daytime lighting. Nighttime lighting. Luminance of the walls and surfaces external to the carriageway. Luminance uniformity. Glare limitation. Light sources and system solutions. Design of an artificial lighting system (brief notes). Energy saving and regulation of system performance. Backup lighting. Maintenance operations of the lighting system. | Text 1 Chapter 8 (Paragraph 8.3 and related sub-paragraphs - pages 311-333) |
| 4 | 4. ROAD INTERSECTIONS: DESIGN CHOICES AND FUNCTIONAL TYPES: Geometric-functional classification of road intersections. Classification of intersections according to DM 19/04/2006. Choice of the type of intersection. Operational performances of intersections: evaluation tools and solutions compared. Safety of intersections: conflicts and risk of collisions. Design choices deriving from the joint analysis of operational performances and safety requirements. Design parameters. | Text 2 Chapter 1 (pages 3-30) |
| 5 | 5. LINEAR AT-GRADE INTERSECTIONS: Introduction. Compositional elements of linear at-grade intersections: specialized lanes and traffic islands. Specialized lanes: admissibility, necessity and minimum transverse dimensions. Traffic islands. Procedural process for the geometric-functional design of linear intersections. Teardrop island and widening of the cross section of the intersection. Edge curves for right turns. Swept paths. Specialized lanes. Central storage lane. Entry lane. Central merging lane. Exit lane. Pseudo-exit lane. Accessory traffic islands. Divisional islands. Directional islands (pseudo-triangular). Refuge islands. | Text 2 Chapter 2 (pages 31-76) |
| 6 | 5. LINEAR AT-GRADE INTERSECTIONS: Sight checks. Stopping sight distance. Maneuver sight distance. Sight triangles. | Text 2 Chapter 2 (pages 76-79) |
| 7 | 6. ROUNDABOUTS: Modern roundabouts: Italian regulations. Main design rule: control of trajectory deflection. Procedural process for the plano-altimetric design of modern roundabouts: Arrangement of the arms. Mutual inclination of the converging branches. Diameter of the circulatory ring. Width of the circulatory ring. Central island. Divisional islands. Entries. Entry curves. Exits. Exit curves. | Text 3 Chapter 1 (pages 33-86) |
| 8 | 6. ROUNDABOUTS: Sight criteria. Sight distance at the intersection (sight to the left). Sight distance for stopping. Cross section of the circulatory ring. | Text 3 Chapter 2 (pages 87-96) |
| 9 | 6. ROUNDABOUTS: Mini-roundabouts: Advantages, disadvantages and application areas. Design criteria. | Text 3 Chapter 3 (pages 99-117) |
| 10 | 6. ROUNDABOUTS: Large diameter roundabouts: Dimensioning of the weaving sections. Geometric design. | Text 3 Chapter 4 (pages 119-133) |
| 11 | 6. ROUNDABOUTS: Grade-separated configurations: Diamond intersection. Semi-cloverleaf intersection. Grade-separated roundabout. Target-roundabout: double grade-separated roundabout with bypass lanes for right turns. | Text 3 Chapter 5 (pages 135-148) |
| 12 | 6. ROUNDABOUTS: Turbo-roundabouts: Classification of turbo-roundabouts. Characteristic elements and design criteria. | Text 3 Chapter 6 (pages 149-162) |
| 13 | 6. ROUNDABOUTS: Safety: Conflicts and conflict points. Accidents in roundabouts: types and causal factors. | Text 3 Chapter 8 (pages 197-207) (pages 212-216) |
| 14 | 6. ROUNDABOUTS: Operational performances: Traffic data acquisition. Methodologies for the performance analysis of approaches to roundabouts (HCM Edition 6 (2016) method, deterministic software, micro-simulation software). | Text 3 Chapter 11 (pages 281-312) |
| 15 | 6. ROUNDABOUTS: Special cases and alternative schemes: Dedicated lanes for right turns. Flower roundabouts. Double elbow roundabouts. Roundabouts with road crossing in underpass. Roundabouts crossed by railway tracks. Mobile roundabouts. | Text 3 Chapter 12 (pages 313-337) |
| 16 | 7. INTERCHANGES: Introduction. Constituent elements of interchanges: ramps and overpass/underpass structures. Types of interchanges. Geometric design of modular elements in interchanges. Diverging section. Intermediate exit section. Constant radius section. Acceleration section. Merging section. Final connection section. Vertical design of ramps. Optimization of longitudinal profiles through vertical inflection points. Weaving zones. | Text 2 Chapter 7 (pages 171-203) |
| 17 | 8. ROAD SIGNS FOR INTERSECTION SAFETY: The role of road signs in road safety. Vertical traffic signs. Road markings. Supplementary signage. Signage plans for linear at-grade intersections and roundabouts. | Text 2 Chapter 8 (pages 205-226); Text 1 Chapter 10 (pages 269-280) |
Learning Assessment
Learning Assessment Procedures
The exam consists of an oral test including references to the design projects carried out during the course.
Students have the option to take two midterm tests. The final grade will result from their outcomes, combined with the oral exam and the evaluation of the group design projects.
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For students who choose to take the two midterm tests, the assessment will take place in four phases:
- Evaluation of the "First midterm test" (November 16, 2026): max 10 points
- Evaluation of the "Second midterm test" (January 11, 2027): max 5 points
- Evaluation of the "Group design projects": max 5 points
- Evaluation of the "Oral exam" (to be taken during one of the scheduled exam sessions): max 10 points
For students who choose NOT to take the two midterm tests, the assessment will be based solely on the single oral exam to be taken during one of the scheduled exam sessions.
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EXAM SCHEDULE AND EVALUATION PROCEDURES
1) First midterm test — November 16, 2026 (during the teaching suspension period)
Structure: Oral exam on the following topics:
- Passive road safety (Ch. 1)
- Road lighting (Ch. 2)
- Tunnel lighting (Ch. 3)
Maximum score: 10 pts.
Passing score: ≥ 6/10.
If score < 6/10: the student may still take the second midterm test, but during the final oral exam they must also answer questions on all topics from the first midterm test.
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2) Second midterm test — January 11, 2027
Structure: Oral exam on the following topics:
- Intersections and design parameters (Ch. 4)
- Roundabout feasibility and planning (Ch. 6)
- Mini-roundabouts (Ch. 6)
- Large-diameter roundabouts (Ch. 6)
- Turbo-roundabouts (Ch. 6)
- Special cases and alternative layouts (Ch. 6)
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Maximum score: 5 pts.
Passing score: ≥ 3/5.
If score < 3/5: during the final oral exam, the student must also answer questions on all topics from the second midterm test.
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3) Merit band after the two midterm tests
The merit band will be calculated following the two midterm tests based on the overall midterm score (VCPI), which is the sum of the scores of both tests (max 15 pts):
- Low merit band: 9 < VCPI ≤ 10
- Medium merit band: 10 < VCPI ≤ 12
- High merit band: 12 < VCPI ≤ 15
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Students whose assessment falls into the low or medium band may improve their evaluation and move to a higher band through an oral interview. This interview must be conducted concurrently with the final oral exam, no later than September 24, 2027 (the last exam call of the third session for regular students).
The interview will cover the midterm test topics (first, second, or both, depending on the targeted improvement).
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4) Final Exam (PF): Oral exam and evaluation of group design projects
4.a) Exam calls from January 18, 2027 to September 24, 2027
Discussion of group design projects (printed sheets in the specified scales and a printed technical report in A4 format).
In-depth questions on the following syllabus topics:
- Chapter 5 of the syllabus (full chapter). At-grade linear intersections: types; auxiliary lanes (definitions, selection criteria, and design: center left-turn lane, acceleration/entry lane, deceleration/exit lane); outer edges; traffic islands (divisional, teardrop, directional, pedestrian refuge); sight distances.
- Chapter 6 of the syllabus (specific topics listed below). Road roundabouts: Italian regulations; deflection control rule; planimetric and altimetric design (arm arrangement, entering branch alignment, central island and circulatory roadway diameter and width, splitter islands, entries/exits and relative curves, sight criteria, sight distances at intersections and stopping sight distances); grade-separated layouts (diamond, partial cloverleaf, grade-separated roundabout, target-roundabout); safety (conflicts and accidents); operational performance (data collection, HCM 2016 methods, deterministic and microsimulation software).
- Chapter 7 of the syllabus (full chapter). Interchanges: main layouts; overpass and underpass structures; ramps (coordination, planimetric and altimetric configuration: diverge/deceleration/constant curvature/acceleration/merge/end sections; weaving areas).
- Chapter 8 of the syllabus (full chapter). Signage and marking for intersection safety: pavement markings, vertical signs, complementary devices; signage plans for at-grade intersections and roundabouts.
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Score: maximum 15 pts (max 10 pts for the oral exam and max 5 pts for the design projects).
Passing score: ≥ 9/15.
Merit bands based on the final exam score (VPF):
- Low merit band: 9 < VPF ≤ 10
- Medium merit band: 10 < VPF ≤ 12
- High merit band: 12 < VPF ≤ 15
Students with a low or medium evaluation may retake the oral interview by September 24, 2027 to improve their evaluation and reach a higher band.
4.b) Exam calls after September 24, 2027
- Discussion of group design projects (as specified above).
- In-depth questions covering all syllabus topics.
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5) Final grade out of 30
The final merit band depends on the combination of the two bands (midterm tests + final exam) according to the following grid:
Band Combination (Midterm + Final) | Final Merit Band | Maximum Grade |
Low + Low | Low | 20/30 |
Low + Medium OR Medium + Low | Medium-Low | 23/30 |
Medium + Medium OR Low + High OR High + Low | Medium | 25/30 |
Medium + High OR High + Medium | Medium-High | 27/30 |
High + High | High | 30/30 |
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6) Common provisions
All exams held after September 24, 2027 will cover the entire syllabus, regardless of the results achieved in the midterm tests.
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Examples of frequently asked questions and / or exercises
1. Conflict points
2. Sight distance checks in roundabouts
3. Sight triangle checks at at-grade intersections
4. Peculiarities of mini-roundabouts
5. The weaving section criterion for sizing large-diameter roundabouts
6. Turbo-blocks in turbo-roundabouts
7. Dedicated right-turn lanes at roundabouts
8. Specialized lanes at at-grade intersections
9. Three-centered curves (referring to compound curves used in intersection radii)
10. Planimetric composition of ramps
11. The perfect inflection point in ramps
12. Operational performance of roundabouts (Capacity, queues, and levels of service)
13. Procedural steps for selecting the type of safety barrier
14. ASI and THIV indices (Acceleration Severity Index and Theoretical Head Impact Velocity)
15. Transitions in safety barriers
16. End terminals of safety barriers
17. Crash cushions
18. Photometric parameters
19. Lighting classes according to the UNI 11248 standard
20. Layout of light points at road intersections
21. Luminance profile inside road tunnels
22. The Adrian diagram (used for veiling luminance calculations)
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24. Concepts of daytime and nighttime tunnel lighting
25. Concepts of short and long tunnels from a lighting perspective