highway engineering

1. Department of civil Engineering
Semester 6
Course Code CIV 321
Course Name Highway Engineering I
Course Teacher: Abdirahman Beder Muse
GOLLIS UNIVERSITY

2. HIGHWAY CROSS SECTION
ELEMENTS AND SAFETY
Chapter 3

3. Introduction
 Roads are
normally used
for
transportation
within a
country.
 Road - A way or path over which cyclists,
vehicles and pedestrians can pass lawfully.

4. Advantages of Roads
Can be used by all types of vehicles from
cycles to trailers.
 Can lead to any remote area and road users
have freedom of movement.
 Vehicle movements are not time bound, roads
are open to traffic for 24 hours

5. Typical Road Cross-Section
Elements
The cross section of a road includes some or all of the
following elements:
 Right of Way
 Carriage way or Traveled way
 Shoulder
 Roadway
 Median
 Kerbs
 Foot Path or side Walk
 Traffic Barriers
 Bicycle and Parking lane
 Drainage channels and side slopes

7. Selection of appropriate cross-
section elements
In selecting the appropriate cross-section elements
and dimensions, designers need to consider a number
of factors:
 Volume and composition (percent trucks, buses,
and recreational vehicles) of the vehicular traffic
expected to use the facility.
 the likelihood that cyclists and pedestrians will
use the route
 Climatic conditions

8. Selection of appropriate cross-
section elements
 The presence of natural or human made
obstructions adjacent to the roadway (e.g. rock
cliffs, large trees, wetlands, buildings, power
lines)

9. Selection of appropriate cross-
section elements
 Safety of the users
The most appropriate design is the one that
balances the mobility needs of the people using the
facility (motorists, pedestrians, or cyclists) with the
physical constraints of the corridor within which
the facility is located.
 Type and intensity of development along the
section of the highway facility that is being
designed

10. Right of Way
Right of way is the area of land acquired for road,
along its alignment. It is the distance between the
boundary stones on
either side of the
rod.

11. Carriage/Traveled way
The width of pavement way on which vehicles
travel is called Carriage way/Travelled way or
pavement width.

12. Carriage/Traveled way
The portion of the roadway provided for the
movement of vehicles, exclusive of shoulders.
 Number of lanes on a traveled way are decided
on the basis of expected traffic volumes and
appropriate level of service required for the
facility.

13. Carriage/Traveled way
Lane width strongly influences traffic safety and
comfort
 Lane width ranges from 2.7-3.6 m with 3.6 m
lane predominant on high type highways
Two-lane two-way highways with the 3.6 m lane
provide safe clearance between large commercial
vehicles

14. Shoulders
Shoulders are the strips provided on both sides of
the carriage way.

15. Functions of shoulders
accommodation of stopped vehicles (disabled
vehicles, bus stops)
emergency use
lateral support for the pavement
space for roadside facilities
space for bicycles and pedestrians
driving comfort (freedom from strain)
improvement in sight distance
improvement in capacity

16. Width of shoulders

17. Width of shoulders
Low-type roads - minimum 0.6 m, recommended
1.8 m
Shoulder provided for bicycles - minimum 1.2 m
wide
High-type roads - minimum 3.0 m, recommended
3.6 m
Shoulders should be continuous.
Shoulders on bridges should have the same width
as on the approach sections.

18. Roadway
The portion of a highway provided for vehicular
use.
It includes both carriageway and shoulders.

19. Roadway

20. Median or Traffic Separators
It is the physical or painted separation provided
on divided highways between two adjacent
roadways.
Medians can also be used to isolate slow and fast
moving traffic in the same direction.
 Width of
medians
ranges from
1.2 to 2.4 m.

21. Median or Traffic Separators

22. Median or Traffic Separators

23. Median or Traffic Separators

24. separate opposing traffic
recovery area for out-of-control vehicles
stopping area
storage of right-turning and U-turning vehicles
Function of medians
storage of right-
turning and U-
turning vehicles
minimize headlight
glare
provision for future
lanes

25. right-turning and U-turning vehicles
Function of medians

26. Formation Width
It is the sum of widths of carriage way, shoulders
and median strips if provided.
In case of embankments, it is measured as the top
width.
In case of cutting, it is the bottom width of the
cutting from which side drains are excluded.

27. Kerb
It is the dividing line between carriageway and
footpath.

28. Kerb

29. drainage control
roadway edge delineation
right-of-way reduction
delineation of pedestrian walkways
reduction in maintenance operation
Assistance in roadside development
Functions of Kerbs

30. Class I Kerb: Height 7-9 cms
Class II Kerb: Height 15-20 cms
Barrier: 23-45 cms
Submerged: provide lateral stability
Types of Kerbs

31. Types of Kerbs

32. Foot paths are provided in Urban roads
These are raised strips constructed along both the
edges of roads.
Their minimum recommended width is 1.3 m.
Foot Path or side Walk

33. Foot Path or side Walk

34. Foot Path or side Walk

35. A longitudinal barrier, including bridge rail, or an
impact attenuator used to
Redirect vehicles from hazards located within an
established Design Clear Zone
To prevent median crossovers
To prevent errant vehicles from going over the
side of a bridge structure
To protect workers (occasionally)
To protect pedestrians, or bicyclists from
vehicular traffic
Foot Path or side Walk

36. Traffic Barriers

37. Traffic Barriers

38. Bicycle lane is a portion of the roadway
designated by striping, signing, and/or pavement
markings for preferential or exclusive use by
bicycles and/or other non-motorized vehicles.
Parking lane is an additional lane provided on
Urban roads and streets.
Bicycle and Parking lane

39. BICYCLE AND PARKING LANE

40. Bicycle and Parking lane

41. DRAINAGE CHANNELS AND
SIDE SLOPES
Drainage channels and side slopes are provided along
the length of road for storm water drainage etc.

42. Drainage channels should:
have adequate capacity for the design runoff
minimize damage to the highway caused by
unusual storm water
minimize risk for motorists
be resistant to the high speed water flows where
expected
prevent sedimentation of the particles carried by
water.
Drainage channels and side slopes

43. Side slopes should
insure the stability of the roadway
provide opportunity for recovery of an out-of-
control vehicle
Drainage channels and side slopes

44. HIGHWAY SAFETY
Part 2

45. Road Traffic safety refers to methods and
measures for reducing the risk of a person using
the road network for being killed or seriously
injured.
The users of road include
Pedestrians
Cyclist
Public transport
Motorists and their passenger
What is Road safety?

46. A traffic accident on a public road may involve a
single road vehicle (e.g. a vehicle which skids and
overturns), or it may involve a vehicle in a
collision (e.g. between a vehicle and one or more
vehicles, a pedestrian, an animal, and/or fixed
object).
What is Road safety?

47. But due to
ignorance of
safety on the
roads there are
accidents
happening on the
road causing
injuries and
deaths.
What is Road safety?

48. 1. More than 1.2 million people are killed in road
accident worldwide every year
2. One child is killed road accidents, every three
minute in the world.
Road accident statistics

49. 3. In Somaliland 136 people were killed, 2549
others injured in car accidents in the first nine
months of 2019.
4. From January to November 2021, Somaliland
recorded 2873 motor accidents According to the
Traffic Unit of the police during this period,
there were 156 fatalities and 1815 injury cases
in road accidents.
Road accident statistics

50. What is Road safety?

51. While the causes of crashes are usually complex
and involve several factors, they can be considered
in four separate categories:
 Actions by the driver or operator,
 Mechanical condition of the vehicle,
 Geometric characteristics of the roadway,
 Physical or climatic environment in which the
vehicle operates.
Factors Involved in Highway Crashes

52. Driver or Operator Action
The major contributing cause of many crash situations is
the performance of the driver of one or both (in
multiple vehicle crashes) of the vehicles involved.
Driver error can occur in many ways, such as
inattention to the roadway and surrounding
Traffic failure to yield the right of way, and/or traffic
laws.
Factors Involved in Highway Crashes

53. Driver or Operator Action
These “failures” can occur as a result of unfamiliarity
with
 roadway conditions.
 traveling at high speeds.
 drowsiness.
 Drinking.
 and using a cell phone or other distractions within
the vehicle.
Factors Involved in Highway Crashes

54. Mechanical condition of the vehicle
The mechanical condition of a vehicle can be the cause
of transportation crashes.
Faulty brakes in heavy trucks have caused crashes.
Other reasons are failure of the electrical system, worn
tires, and the location of the vehicle’s center of
gravity.
Factors Involved in Highway Crashes

56. Geometric characteristics of the road way
The condition and quality of the roadway, which
includes the pavement, shoulders, intersections, and
the traffic control system, can be a factor in a crash
Factors Involved in Highway Crashes

57. Geometric characteristics of the road way
Highways must be designed to provide adequate sight
distance at the design speed or motorists will be
unable to take remedial action to avoid a crash.
Traffic signals must provide adequate decision sight
distance when the signal goes from green to red.
Highway curves must be carefully designed to
accommodate vehicles traveling at or below the
design speed of the road.
Factors Involved in Highway Crashes

58. Geometric characteristics of the road way
Factors Involved in Highway Crashes

59. The Environmental condition
The physical and climatic environment surrounding a
transportation vehicle can also be a factor in the
occurrence of transportation crashes with the most
common being weather.
Factors Involved in Highway Crashes
All transportation
systems function
at their best when
the weather is
sunny and mild
and the skies are
clear.

60. The Environmental condition
Weather on roads can contribute to highway crashes;
for example,
Many severe crashes have been caused by fog because
vehicles traveling at high speeds are unable to see
other vehicles ahead that may have stopped or slowed
down, creating a multivehicle pile-up.
Flooded river plains, swollen rivers, and mud slides
on the pavement have caused railroad and highway
crashes.
Factors Involved in Highway Crashes

61. The Environmental condition
Factors Involved in Highway Crashes

62. The Environmental condition
Factors Involved in Highway Crashes