Unit 1PLANNING AND DESIGN FOR ROADS AND BRIDGESPART 1PLANNING AND DESIGN FOR ROADS1. READINGThe Highway Classification SystemHIGHWAY CLASSIFICATIONSThe classification of highways is necessary for communication among engineers, administrators, and the general public. Different classification schemes have been applied for different purposes in different rural and urban regions. Classification of highways by design types based in the major geometric features (e.g., freeways, conventional streets, and highways) is the most helpful one for highway location and design procedures. Classification by route numbering (e.g., U.S., State, County) is the most helpful for traffic operations. Administrative classification (e.g., National Highway System or NonNational Highway System) is used to denote the levels of government responsible for, and the method of financing, highway facilities. Functional classification, the grouping of highways by the character of service they provide, was developed for transportation planning purposes. Comprehensive transportation planning, an integral part of total economic and social development, uses functional classification as an important planning tool.
Trang 1Unit 1 FOR ROADS AND BRIDGES PLANNING AND DESIGN
1 READING
The Highway Classification System
a What do you think when you see a new road? Complete the diagram below.
Now, compare your diagram with your partners.
b In groups, discuss the different types of classifying highways
How many categories are there?
What are the purposes of the highway classifications?
c Read the first paragraph of Highway Classifications and complete the following table.
Highway
location and design
- freeways, conventional streets, and highways
Speed
Width
Safety
Landscape
THE ROAD
THE ROAD
Trang 2By route numbering
Administrative
classification
Functional
classification
HIGHWAY CLASSIFICATIONS
The classification of highways is necessary for communication among engineers, administrators, and the general public Different classification schemes have been applied for different purposes in different rural and urban regions Classification of highways by design types based in the major geometric features (e.g., freeways, conventional streets, and highways) is the most helpful one for highway location and design procedures Classification by route numbering (e.g., U.S., State, County) is the most helpful for traffic operations Administrative classification (e.g., National Highway System or Non-National Highway System) is used
to denote the levels of government responsible for, and the method of financing, highway facilities Functional classification, the grouping of highways by the character of service they provide, was developed for transportation planning purposes Comprehensive transportation planning,
an integral part of total economic and social development, uses functional classification as an important planning tool
Functional classification is the process by which streets and highways are grouped into classes according to the character of traffic service that they are intended to provide There are three highway functional classifications: arterial, collector, and local roads All streets and highways are grouped into one of these classes, depending on the character of the traffic (i.e., local or long distance) and the degree of land access that they allow These classifications are described in Table
1
Trang 3the longest uninterrupted distance, with some degree of access control
Collector provides a less highly developed level of service at a lower
speed for shorter distances by collecting traffic from local roads and connecting them with arterials
Local consists of all roads not defined as arterials or collectors;
primarily provides access to land with little or no through movement
Typically, travellers will use a combination of arterial, collector, and local
roads for their trips Each type of road has a specific purpose or
function Some provide land access; others provide travel mobility at
varying levels
There is a basic relationship between traffic mobility and land access, as
illustrated in Figure 1
Land Access
Mobility
Arterials
higher mobility
low degree of access
Collectors
balance between mobility and access
Locals
lower mobility
high degree of access
Trang 4Figure 1 Relationship of functionally classified highway systems in
serving traffic mobility and land access
Once the functional classification of a particular roadway has been
established, the allowable range of design speed, the principal limiting
design parameters, and horizontal and vertical alignment have also
defined Similarly, functional classification establishes the basic roadway
cross section in terms of lane width, shoulder width, type and width of
median area, and other major design features (see Figure 2)
Figure 2 The flexibility available to a highway designer is considerably
limited once a particular functional classification as been established
The importance of the functional classification process as it relates to
highway design lies in the fact that functional classification decisions are
made well before an individual project is selected to move into the design
phase Moreover, such decisions are made on a systemwide basis by city
or county as part of their continuing long-range transportation planning
functions Thus, the functional classification of a particular section of
highway may well represent a decision made 10 or more years ago
d Match the terms to the definitions
movement with low level of accessibility
Trang 5but a low level of mobility.
geometric features of the roadway
Arterial road Collector road Local road
e Fill in the blank with suitable words
1 All streets and highways are grouped into one of these classes,
depending on the character of the traffic and the degree
of that they allow
2 Travellers will use a of arterial, collector, and local
roads for their trips
3 Collector roadways provide a balance between and
land access
4 provides the highest level of service at the greatest
speed for the longest uninterrupted distance
5 A determination of functional classification establishes the basic
roadway
6 Functional classification decisions are made as part of their continuing
long-range functions
f Decide whether the following statements are True (T) or False (F)
1. Arterial, collector and local are grouped into highway
functional classifications
2 Traffic mobility and land access don’t have any relationship
3 Local roads provide a high level of access to adjacent
properties but a low level of mobility
Trang 64. Without defining the allowance range of design speed, horizontal and vertical alignment can’t be defined
5 The functional classification of a particular section of highway may well represent a decision made 10 or more years ago
Trang 73 SPEAKING
In pairs, describe the figure 1 Relationship of functionally classified
highway systems in serving traffic mobility and land access using
comparison of adjectives.
Arterials provide higher mobility than collectors and locals
4 READING AND WRITING
a Complete the table with the appropriate descriptions of Functional
Classification.
A Highways generally providing direct service between cities and
important economic, political, cultural centres; Partial Controlled
Access Highways; ≥4 lanes
B. Local Roads providing direct service between districts, cooperatives,
etc
C Super high class Highway for high speed traffic with controlled
access and quick travel time, providing transport service between
large important cities
D Highways providing direct service between several towns and local
economic, political, cultural centres Roads connecting them to the
arterial network and expressways
E. Highways providing direct service between big economic, political,
cultural centres; Road connecting them to the Ind category or
expressways – 2 lanes
ry Traffic
Volume
PCU/day
Functional Classification
Technical Classification Administrati
ve Classificatio n
Level Rollin
g
Mountainou s
>25000
120 100
100 80
80 60
National Road
110 100
90 80
70 60
National Road
60
60 40
50 30
National or Provincial
Trang 8IV
≤200-1 lane
>
200-2 lanes
60 40
40 30
30 20
Local Road
b Translate the above table into Vietnamese.
Grammar focus: Zero relative clause (Omitting relative pronouns)
E.g Arterials are the highways providing the highest mobility.
(understood: Arterials are the highways which provide the highest mobility)
HIGHWAY CROSS-SECTION ELEMENTS
1 VOCABULARY BUILDING
a Guess the meaning of the following terms.
Right-of-Way
Clearing Limits
Cut Slope (Back Slope)
Natural Ground
Ditch
Road bed
Subgrade Traveled Way
Toe of Slope
Fill Slope
(Embankment)
Base Course Surface Course
Roadway (Construction Limits)
CL
Trang 9b Label the following cross-section elements.
Median
MEDIAN
Cross-section Elements for a Divided Highway
Trang 10Curb Railing/Wall barrier Shoulder (Outer) Roadway
2 LISTENING
a What is a safe highway? How can we design a safe highway?
b Watch a video and choose the best answer (A, B, C, or D) for the following sentences.
1 will be a new arterial highway for Japan
Expressway
2 We aim to make this the world’s safest, most pleasant expressway co-existing harmoniously with
3 We are engaged in a wide range of measures to accidents on expressways
minimize
4 We have widened the road, reduced and so decreased driver stress and improved road visibility
curves
5 We have made traffic signs and much easier to read by improving the colors and shapes based on intensive testing
side road
6 The expressway is paved with paving material
conventional
Trang 117 The expressway has been planned and designed anticipating a possible
earthquake
8 In addition to being light and pleasant to drive through, we have employed lighting consuming less power than conventional lights
environment-friendly
9 We use advanced systems with TV cameras to monitor the entire expressway
observing
c Watch again for more information What have they done to make New Tomei Expressway the world’s safest, most pleasant expressway?
Trang 123 SPEAKING
HORIZONTAL AND VERTICAL ALIGNMENT
Horizontal and vertical alignments are permanent elements that should not be designed independently They complement each other, and poorly designed combinations can spoil the good points and aggravate the deficiencies of each Working drawings, with the profile plotted jointly with the plan, assist in analyzing the horizontal alignment and profile relationship in roadway design.
Indicate in the following figures whether the layout is a good or poor highway design practice by checking the appropriate box
Useful expressions:
PLAN
PROFILE
This combination presents a poor appearance – the
horizontal curve looks like a sharp angle
1 Sharp angle appearance
PLAN
PROFILE
When horizontal and vertical curves coincide, a very satisfactory appearance results
2 Coinciding curves in horizontal and vertical direction
C rest
Good design practice Poor design
practice
Good design practice Poor design
practice
PLAN
PROFILE
The classic case of coordination between horizontal and vertical
alignment in which the vertices of horizontal and vertical curves
coinc ide, creating a rich effect of three -dimensional S-curves
composed of convex and concave helixes
3 Coinciding vertices in horizontal and vertical dimensions
PLAN
PROFILE
When horizontal and vertical curves oppose, a very satisfactory appearance results
4 Opposing curves in horizontal and vertical direction
Sag
I think
so
I don’t
Probably.
Because
.
Trang 13 Good design practice Poor design
practice
Good design practice Poor design
practice
PLAN
PROFILE
A legitimate case of coordination: one phase is skipped in the
horizontal plane, but vertices still coincide The long tangent in
plan is softened by vertical curvature
5 Coinciding vertices with single phase skip
PLAN
Very long flat curves, even when not required by a design speed and regardless of profile, also have a pleasing appearance when the central angle is very small
6 Horizontal alignment with small central angles
Minimum curve for the design speed
Desirable curve for appearance
Good design practice Poor design
practice
Good design practice Poor design
practice
PLAN
PROFILE
7 Weak coordination of horizontal and vertical alignment
PLAN
8 Horizontal alignment should be balanced
The upper line is an example of poor design because the alignment consists of a long tangent with short c urves, whereas the balance between the curves and tangents in
the lower alignment is preferred design
Good design practice Poor design
practice
Good design practice Poor design
practice
Preferred
PLAN
Avoid designing little local dips in an otherwise long, uniform
grade These dips usually result from a desire to balance cut
and fill and reduce overhaul
9 Profile with tangent alignment
PROFILE
PLAN
Short humps in the grade should be avoided
10 Profile with curve ali gnment
PROFILE
Preferred
Good design practice Poor design
practice
Good design practice Poor design
practice
Trang 14PLAN
A distant side view of a long grade on tangent will reveal
every bump on it
11 Distant view showing bumps in profile gradeline
Preferred
Line of sight across open bottom lands
PLAN
This combination is defic ient for two reasons: the tangent between the curves is too short and the reverse occurs on a crest
12 Short tangent on a crest between two horizontal curves PROFILE
Good design practice Poor design
practice
Good design practice Poor design
practice
PLAN
A disjointed effect occurs when the beginning of a horizontal
curve is hidden from the driver by an intervening crest while
the continuation of the curve is visible in the distance beyond
the intervening crest
13 Disjointed eff ect
PROFILE
Line of sight
PERSPECTIVE
PLAN
G uideline to be used for coordination of horizontal and vertical alignment
PROFILE
Horizontal alignment view – 2 breaks maximum
View
Vertical alignment view – 3 breaks maximum
View
14 Good coordination of horizontal and vertical alignment
Good design practice Poor design
practice
Good design practice Poor design
practice