Appunti Design of Transportation Infrastructures 2020

DESIGN OF TRANSPORTATION INFRASTRUCTURES 2020 – SUMMARY

1. GEOMETRIC DESIGN OF ROADS

• DESIGN PRINCIPLES AND CONSTRUCTION PROCESS

• INFRASTRUCTURE DESIGN: ITALIAN POLICY

Sight distances

o Alignment

o Curvature, speed and superelevation

o Geodetic slope control

o Transitions: variable radius curves (clothoid)

o Superelevation along transitions

o Carriageway enlargement

o Vertical alignment

o Speed diagram

o

2. STRAIGHT, HORIZONTAL CURVES FOR ROADS TRANSITIONS, INFLECTIONS AND CONTINUITIES

• ELEMENTS OF HORIZONTAL ALIGNMENT

Design of straights (tangent) and horizontal curves

o Design of transitions (clothoids)

o

3. DESIGN CONSISTENCY: DESIGN AND OPERATING SPEED CONCEPTS

• DESIGN SPEED PROFILE

• OPERATING SPEED

4. SIGHT ANALYSIS

• AVAILABLE SIGHT DISTANCE (ASD)

• STOPPING SIGHT DISTANCE (SSD), PASSING SIGHT DISTANCE (PSD) AND CHANGE LANE SIGHT DISTANCE (CLSD)

5. ROAD FUNCTIONS AND CLASSIFICATION, CROSS SECTIONAL ELEMENTS AND COMPOSITION, OPERATIONAL ANALYSIS

• CROSS SECTIONS – Rural and Urban

• OPERATIONAL ANALYSIS – HCM (Highway Capacity Manual) methodology for the Level of Service calculation

• OPERATIONAL ANALYSIS OF FREEWAYS AND MULTILANE HIGHWAYS

• OPERATIONAL ANALYSIS OF TWO-LANE RURAL HIGHWAYS

6. ROAD SECTION ORGANIZATION

• CROSS SECTIONAL ELEMENTS

Median and shoulders

o Natural elements

o Artificial elements, Underpasses, Tunnels, Lay – bys, Climbing lanes

o

• VERTICAL ALIGNMENT DESIGN

• INTERFERENCES ANNOTATIONS FOR RIVERS AND EXISTING INFRASTRUCTURES

7. INTERSECTIONS

• ANALYSIS AND DESIGN OF MANEUVERS IN INTERSECTIONS

• AT GRADE INTERSECTIONS: GENERAL DESIGN CRITERIA

• AT GRADE INTERSECTIONS: CURVES

• AT GRADE INTERSECTIONS: SIGHT ANALYSIS

8. ROUNDABOUTS

• MODERN ROUNDABOUTS: PRINCIPLES AND GEOMETRY

• BASIC DESIGN PRINCIPLES

Key geometric elements and prescriptions

o

9. INTERCHANGES

• INTRODUCTION

• RAMP DESIGN SPEED AND GEOMETRIC CHARACTERISTICS

• RAMPS ALIGNMENT FOR RAMPS/TERMINALS LANE WIDTH

• INTERCHANGES EXAMPLES

Two quadrant interchanges

o Diamond interchanges

o Cloverleaf and all directional four-leg interchanges

o Trumpet and three-legs directional (T) interchanges

o

10. SAFETY (TRAFFIC) BARRIERS FOR ROADS

• LONGITUDINAL BARRIERS: FLEXIBLE AND RIGID

• DESIGN RULES

• EXAMPLES OF SAFETY BARRIERS, CRASH CUSHIONS AND TERMINALS

11. ROUNDABOUTS: OPERATIONAL ANALYSIS (HCM)

• Capacity for single and two lanes

• Operational analysis steps

12. INTERCHANGES: OPERATIONAL ANALYSIS (HCM)

• WEAVING AREAS

Measure of configuration in one-sided weaving areas

o Operational analysis steps

o

• FREEWAY RAMPS

Operational analysis steps

o

• INTEGRATIONS AMONG ITALIAN STANDARDS AND HCM

13. CROSS SECTIONS AND COST ESTIMATION

• TEMPLATE SECTIONS AND CROSS (TRANSVERSAL SECTIONS)

• QUANTITIES AND COST ESTIMATION

Parametric method

o Analytic method – Simpson formula

o Total cost table

o

• CONSTRUCTION COSTS (W) AND UNIT COSTS

- Lecture 18 – RAILWAYS (slides)

- Lecture 19 – AIRPORTS (slides)

DESIGN OF TRANSPORTATION INFRASTRUCTURES

GEOMETRIC DESIGN OF ROADS (ITALIAN STANDARDS)

Design and engineering

Design is creating a plan or convention for the construction of objects or systems: in other words, it is the action of

conceiving a drawing and a plan of something before it is made. Engineering is the creative application of scientific

principles to design and develop structures, machines or manufacturing processes, respecting the principles of economics

of operations and safety of life.

DESIGN PRINCIPLES AND COSTRUCTION PROCESS

There are some overall objectives in designing constructions:

a) High quality and durability

b) Safety, both for workers and users

c) Highest benefit/costs ratio

d) Environmental sustainability

e) Respect of national laws, technical standards, contracts, road engineering principles

The whole construction process is defined as made of steps: 1) Planning [= studio di fattibilità] 2) Design (Preliminary

project, Definitive project, Detailed project [= progetto esecutivo]) 3) Competition 4) Contractor choice 5) Work delivery

6) Construction 7) Final delivery. There could be also a “build project”, drawn up to show the progress of construction.

A road project can be related to:

A new infrastructure built totally on a new alignment. It is necessary to start with the knowledge of the area and

à

o its conditions. The designer should be able to identify corridors of sufficient width from origin to destination,

considering urban, recreational and natural areas, built heritage, natural elements. By overlaying those surfaces

(overlay of thematic maps technique, through GIS software), the designer obtains the alignments which are

environmentally acceptable.

An existing infrastructure:

o a. 3R = Resurfacing [ripavimentazione], Restoration [ripristino], Rehabilitation [recupero]. the focus is on the

à

preservation and extension of the facilities’ service life and/or the safety enhancement. Resurfacing, pavement

structural repair, bridge repair or lane widening are some of the interventions included.

b. 4R = the previous ones + Reconstruction. re-building an infrastructure along an existing alignment. Full-depth

à

pavement or track (railways) replacement, infrastructure conversion and reconfiguration of intersections are

typically involved in this process. It may also include substantial alignment changes.

As already said, the design process is composed by 3 steps, in order to use a gradual approach to design, creating the

involvement of stakeholders in the design process:

1) Preliminary stage progetto di fattibilità tecnica ed economica. It includes the comparative analysis of a minimum

à

of 3 alternatives and the consequent selection of the best one. In this phase, expropriation begins and preliminary

cost estimations are made, basing on contract specifications [capitolato d’appalto], geometric data and drawings:

- Plans (1:10000 – 1:5000)

- Profiles (1:10000/1:1000 – 1/5000/1:500)

- Template sections [sezioni tipo] (1:200)

2) Definitive stage progetto definitivo. It contains the best solution considered in the Preliminary Study. Geometric

à

data, preliminary design reports, materials, definitive costs estimations and more detailed drawings are explored in

this phase. Here ends the expropriation process, presenting and discussing the project with all the stakeholders.

3) Final-detailed stage progetto esecutivo. It explores every detail of the infrastructure: dimension, typology, also

à

specified for every component, final cost estimation, more detailed drawings. In this stage the Maintenance Program

is given to the owner as a result of material selection, structural characteristics and environmental condition. The

project is given to the Contractor.

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M. Bassani: Design of Transportation Infrastructures (a)

Francesco Torre, 2020/2021 1

INFRASTRUCTURES DESIGN: ITALIAN POLICY

Roads, railways and airports are public properties, so the design and construction process must follow a well-defined

procedure, in order to guarantee the possibility to any contractor to provide the best design solution. The fundamental

law to operate in Italy is D.lgs 50 – 18 aprile 2016 [Codice dei Contratti]. Besides, there are specific technical rules for

each field: roads (MIT), railways (RFI), airports (ENAC).

The application of road design standards is, according to the Italian current law, mandatory in new constructions and

optional in 3R-4R interventions. Typically, it is optional in other countries. The focus is put on:

SIGHT DISTANCES

o

Appropriate available sight distances (ASD) are necessary and mandatory as a primary safety condition for circulation.

ASD is the length of the road segment that a driver can see in front without considering traffic, weather conditions and

lighting. It must be compared following these relationships:

These requirements must be satisfied in the following moments:

a. On emergency stop. In every road type, especially in urban roads, in order to increase the driver’s reaction time.

b. During an overtake of slower vehicles. Where admitted on two-lane highways and on at least 20% of road length.

c. During a change line in case of exit or road junction, at intersections and deviations.

ALIGNMENT

o

Design starts from this. It is the main line that shows the

infrastructure: on this line, no angular points are

admitted.

It’s made up by 3 segments:

1. Straight

2. Constant radius arcs

3. Variable radius arcs, included between two constant

radius arcs

The horizontal surface is represented on a plane.

The vertical one is represented by a cylindrical surface which follows the horizontal alignment. The alignment is taken in

the middle of the cross section.

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M. Bassani: Design of Transportation Infrastructures (a)

Francesco Torre, 2020/2021 2

Some prescriptions on alignment are:

- Tangent length L (between L and L )

t t, min t, max

- Constant radius curves: R > L , when L < 300 m / R 400 m, when L 300 m

t t t

- Cross slopes, to let the rain go away from the road:

2,5% min. on tangent; 7% max on rural roads; 5% max on urban arterials; …

- Rules for the vehicle stability on curves: Only for A, B, C and F-rural roads

CURVATURE, SPEED AND SUPERELEVATION

o GEODETIC SLOPE CONTROL

o

It’s defined as a combination of both longitudinal and cross slopes:

TRANSITIONS: VARIABLE RADIUS CURVES (CLOTHOID)

o

Curves with variable radius are done using clothoids. It is expressed this way:

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M. Bassani: Design of Transportation Infrastructures (a)

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There are some rules in defining the scale factor (A), in order to limit some negative effects:

1) To limit the so-called jerk effect (= variation of lateral acceleration in function of time, during a curve for example).

During calculation we can refer at two equations:

2) To limit the rolling effect [sbandamento].

3) To identify circular and transition curves R/3 < A < R

à

Not permitted curve design solutions in Italy and in other countries are provided in order to guarantee a safe and simple

task for the driver during a curve:

- Curve without circle

- False oval

- Consecutive transition curves.

SUPERELEVATION ALONG TRANSITIONS

o

We can design a superelevation profile over a curvature

diagram, in order to design the superelevation in a transition.

Only the elevation of external edge (at the left in the figure) is

increased at first, until it reaches out the plane of the internal

one, forming a flat inclined surface. Then, the two edges

rotate together to maintain a unique inclination.

i is the minimum longitudinal slope of the carriageway edge

min

necessary to allow sufficient pavement drainage. In fact, in

this critical point the only possibility to let the water go away

is in the longitudinal direction (and then using the cross

slope). (a)

Focusing the attention on the central part of this road,

that’s the situation we see in the case (a) where, in the

inflection point the surface is flat: it is critical because the

water only can be moved away from the carriage

longitudinally. In the continuity situation, there is no

problem: the cross slope (at 2,5%) works on its own.

CARRIAGEWAY ENLARGEMENT

o continuity

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M. Bassani: Design of Transportation Infrastructures (a)

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VERTICAL ALIGNMENT

o

The first line which represents the horizontal alignment is

elevated on the z axle: there are straight elements (grades or

gradients [livelletta]) and curve elements (made of vertical

parabolic arcs – parabolas).

There are some prescriptions about this:

1. Maximum grades are defined in function of:

- Road category

- Context

- Could be +1% if vehicle performance and traffic are not compromised

- Must be < 4% in tunnels of two-carriageway roads

2. Vertical curves:

- Parabola sag and crest [concavo/sacca e convesso/dosso]

à

- It’s similar to circular arcs but more comfortable.

with the convention: - Upgrade ; + Downgrade

Design formula of parabola:

2

First term (multiplied by x ): length of the vertical curve

Second term (multiplied by x): slope of the first grade

The parabola can be approximated to an osculating

circle radius. When we calculate a circular curve, the

standards provide the optimum R value.

v

The external distance f is the distance between the

curve and the vertex.

There is some prescription on R value:

v, min

1. Minimum values to avoid contact of the vehicle body with the road surface. This risk is possible if the R value is too

v

small. The minimum is:

- 20 m in case of sags

- 40 m in case of crests

2. Minimum value for comfort, in function of acceleration and design speed à

3. Minimum values for sight

conditions both during the day

and the night: the radius affects

also the portion of road that the

driver can see in front of him.

4. Minimum values in sags [sacche].

5. Minimum values in crests [dossi].

These last two cases are provided by the standards in charts. The minimum R value is expressed in function of SSD

v

(Stopping Sight Distance) and PSD (Passing Sight Distance), on two-lane highways for instance.

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M. Bassani: Design of Transportation Infrastructures (a)

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o SPEED DIAGRAM

It represents the design speed trend along the road axis, built only on the basis of horizontal alignment.

Starting from the curvature diagram:

- Flat lines: constant radius curves (circular arcs)

- Inclined lines: clothoids

From the relationships between curvature and speed, we can derive

the design speed profile along constant curve elements (included

tangent). The standards don’t allow big speed variation: we have to

provide a constant small variation of speed and not instantaneous big

variations, which would be uncomfortable and unsafe. In instance,

between a tangent and a curve, variation of more than 10 km/h are

not allowed. In particular:

Other factors on speed diagram must be considered:

1. Adapting speed and curves enter ASD = Available Sight Distance

à

2. Horizontal vertical coordination it’s better to work combining the vertical alignment with the horizontal one,

à

analyzing them contemporary.

3. Avoiding situation where the driver can see a road segment ahead after a crest that is too close to the driver itself.

This uncomfortable condition can be avoided following the standards rules provided by the policy.

STRAIGHT, HORIZONTAL CURVES FOR ROADS TRANSITIONS, INFLECTIONS AND CONTINUITIES

Primarily, the figure represents some

examples of classical sections of typical

F F roads facilities (sideway [marciapiede] is

U R mandatory for urban roads, not for rural),

depending on the context and increasing in

E C design speed. It is important to observe the

trend increasing design speed – increasing

accepted LoS).

B

D

A A

U R

ELEMENTS OF HORIZONTAL ALIGNMENT

1. Straight L = length of the straight

à G

2. Circular arc R = radius; L = length of circular arc

à B

3. Transition curve L = length of transition curve; R = radius at the end

à 0 In terms of symbols and annotations, it is important to follow the indications

represented in the left figure, leaving the annotations perpendicular to the

alignment, without changing the orientation.

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M. Bassani: Design of Transportation Infrastructures (a)

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Design of straights (tangent) and horizontal curves

Straights and tangents are equivalent terms. The Italian policy provides limits to L (straight length), in order to avoid

s

negative effects for the drivers, due to monotony and distraction. The straight must be of a length L :

s

1. (maximum design speed for the road category, expressed in [m/s])

2.

For horizontal curves, there is a chart to be used (p. 3), to avoid the use of consecutive radii with large differences. Besides,

to have the correct perception of the presence of a circular arc in a curve, and to provide an adequate balance between

the characteristics of straights and curves (avoid unexpected situations):

1.

2. Assuming R > R :

1 2

- R > L when L < 300 m

2 S S

- R 400 m when L 300 m

2 S

In general, it is possible to solve radius selection

problems considering a range of possible R values, in

function of the road type and the speed interval. These

ranges indicate the cross-slope value associated to the

design speed value.

Between R and R*, the speed is a design speed value

min

between a maximum and a minimum V

à d

Besides, from stability analysis along curves, curvature/speed/superelevation relationships are provided (log scale for

both the axis):

These are relevant design speed and radius values, reported for

each road type (R=rural; U=urban):

V [km/h]; R [m]

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M. Bassani: Design of Transportation Infrastructures (a)

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Design of transitions – clothoids

Transitions are fundamental elements in infrastructures design. It provides

a smooth change of lateral acceleration (jerk effect – J depends on V )

max d

and vehicle roll angle, helping the driver in the vehicle control, giving him

the chance to have a correct visual interpretation of the road alignment.

In particular, the presence of a transition let the driver understand the real alignment, while the absence of it could make

him think of a reduction of width or vertical alignment variation (even if they’re not real!). So, for comfort and safety

reasons, transitions are