Efficiency & Safety of Bridges

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ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE STUDIES
MASTER’S THESIS PROPOSAL
IDENTIFICATION
Name:
TEGEGNE ESHETU
Faculty:
TECHNOLOGY
Department:
CIVIL ENGINEERING
Major:
ROAD & TRANSPORT ENGINEERING
Advisor:
GIRMA BERHANU (Dr. - Ing.)
Title of Thesis:
SAFETY AND EFFICIENCY ON BRIDGES
May, 2010
Table of Contents
Introduction .................................................................................................................................................. 1
Statement of the problem ............................................................................................................................ 1
Objective ....................................................................................................................................................... 2
Literature review........................................................................................................................................... 3
Methodology................................................................................................................................................. 5
Time Schedule ............................................................................................................................................... 6
Thesis Cost .................................................................................................................................................... 7
References .................................................................................................................................................... 8
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Safety and Efficiency on Bridges
Introduction
Nationally bridges and bridge approaches have been identified as one of the leading locations for
severe, single-vehicle crashes. There are many bridges and large culverts on the highway system.
Most have rigid rails and often span a potentially hazardous feature. Many of these structures
were built decades ago for highways of lower speed and less traffic. Because of the high cost of
replacing bridges and the long service life of many bridges, replacement of the bridge or major
component of a bridge, such as the bridge deck or bridge rails, may not be a priority while the
bridge remains structurally adequate. In situations where it is considered inappropriate to
reconstruct the bridge or some element of the bridge to current standards, temporary
improvements, while not resolving a substandard condition, can significantly contribute to
improving highway safety. A temporary safety improvement may be considered when work is
done to improve the safety or reduce the potentially hazardous nature of components or features
of the bridge or roadway approaching the bridge. A safety improvement is considered temporary
when it doesn't fully satisfy the needs of the road user and current design standards, but provides
a significant improvement over existing conditions to warrant its application until the bridge
and/or the approach roadway can be reconstructed to current design standards.
Statement of the problem
The increase in traffic volume and speed of vehicles in recent years has resulted in many
accidents and hence the need arose to give more attention to reduce the hazards which may be
causing accidents on Bridge Approaches and on Bridge Structures. it is taken as a problem that
vehicles and sometimes pedestrians are more often involved in injury accidents.
A bridge safety problem, for example can be described in-terms of,
i. a high number of accidents,
ii. a high accident rate or
iii. a high proportion of serious injuries
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Although a lot of research has been carried out on the Safety design of Highways, very little
work has been done on Safety and Efficiency of Highway Bridges.
Therefore, knowing the factors contributing accidents on bridges will greatly help reduce the
severity and frequency of accidents near the bridge.
Objective
The objective of this study is to identify a set of factors that affect traffic safety on bridges such
as bridge related, approach roadway related and environmentally related so as to enable
preventative measures to be implemented to reduce longer term hazards at the bridge sites. A
detailed accident analysis of a selected number of bridges on a specific project will be conducted
to verify these factors and to obtain insights into bridge accidents.
2
Literature review
The safety, functionality, and structural adequacy of bridges are key components necessary to
support and ensure the safe, reliable and efficient operation of transportation infrastructure and
systems which provide mobility of people and the movement of goods and services.
As per the research paper published by one Agency,
a minimum bridge safety program
components necessary for bridges to ensure an adequate and economical program for the
inspection, evaluation, maintenance, rehabilitation, and replacement of bridges should be
adopted . According to the research paper, such programs as a minimum should include;

Regular programs of inspection and evaluation that incorporate state-of-the-art
investigative and analytical techniques, especially of older bridges which were not
designed and constructed to current design loading and geometric standards;

Posting of weight and speed limits on deficient structures;

Implementing and adequately funding regular system-wide maintenance programs that
are the most cost-effective means of ensuring the safety and adequacy of existing bridges;

Establishing a comprehensive program for prioritizing and adequately funding the
replacement of functionally obsolete and structurally deficient bridges; and
Regarding nighttime safety, about 20 years ago, a few highway agencies began to design and
install low-mounted, lineal-type lighting systems--almost all of which produce a flicker--on a
number of bridges under the assumption that such lighting was an improvement over
conventional lighting systems. This assumption was never validated. One such installation was
the San Mateo Bridge over San Francisco Bay. Theoretically, the length of this bridge should
provide sufficient exposure to this lighting to induce the adverse neurological effects. The
availability of detailed accident records for the San Mateo Bridge provided a basis for
determining whether the nighttime safety on this bridge was in any way related to the amount of
time a motorist was exposed to this lighting system. The analyses of the accident data have
shown that the nighttime safety on the bridge has been adversely affected by the lineal lighting,
that the effect occurs after only about 3 min exposure to the lineal lighting, and that replacement
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of this type of lighting with conventional overhead lighting promotes a safer nighttime traffic
environment.
In summary, Bridge safety inspection shall include the recording of information on the following
traffic safety features so that the evaluation of their adequacy can be made.
(A) Bridge railings: Some factors that affect the proper functioning of bridge railing are
height, material, strength, and geometric features. Railings must be capable of smoothly
redirecting an impacting vehicle. Bridge railings should be evaluated using the current
AASHTO Standard Specifications for Highway Bridges, which calls for railings to meet
specific geometric criteria and to resist specified static loads without exceeding the
allowable stresses in their elements. Bridge railing should be crash tested per FHWA
policy. Railings that meet these criteria and loading conditions are considered acceptable.
(B) Transitions: The transition from approach guardrail to bridge railing requires that the
approach guardrail be firmly attached to the bridge railing. It also requires that the
approach guardrail be gradually stiffened as it comes closer to the bridge railing. The
ends of curbs and safety walks need to be gradually tapered out or shielded.
(C) Approach guardrail: The structural adequacy and compatibility of approach guardrail
with transition designs should be determined. Rarely does the need for a barrier stop at
the end of a bridge.
Thus, an approach guardrail with adequate length and structural qualities to shield
motorists from the hazards at the bridge site needs to be installed. In addition to being
capable of safely redirecting an impacting vehicle, the approach guardrail must also
facilitate a transition to the bridge railing that will not cause snagging or pocketing of an
impacting vehicle.
(D) Approach guardrail ends: As with guardrail ends in general, the ends of approach
guardrails to bridges should be flared, buried, made breakaway, or shielded. Design
treatment of guardrail ends is given in the AASHTO Roadside Design Guide.
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Methodology
The methodology developed for assessing the safety and traffic operational quality of some
bridges on specified bridges. The methodology presented here will be developed as part of a
study conducted to provide recommendations on the maintenance and preservation of these
bridges. As part of the study, two components will be evaluated:
i. traffic safety,
ii. traffic operational quality( efficiency).
The methodology to be used for quantifying the safety and traffic operational aspects of the
study will be as follows.
1. Traffic accident data at selected bridges will be collected from the nearby traffic police
station or other relevant bodies.
2. To assess traffic safety, two different rating systems will be used to quantify traffic safety
operations, and rate the structures in their priority for improvements.

the Bridge Safety Index, and

the Widening Priority Rating.
3. To assess traffic operational quality at the selected bridges, the Highway Capacity
Manual methodology for two-lane highways will be used,
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Time Schedule
The planned schedule for the thesis is shown in Table 1. The total time to
complete the research is about four months starting from September 2010.
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Thesis Cost
The cost required to accomplish the research work is presented below. Table 2 shows the main
items required to conduct the research work.
Table 2: Cost Breakdown
NO.
Item
Cost (ETB)
1
Data Collection, gathering required resources
2,500
2
Stationary materials,
1,500
3
Typing and Editing
1,000
4
Transportation
1,500
TOTAL
6,500
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References
1. The “ Roadside Design Guide,” American Association of State Highway and
Transportation Officials.
2. Sadqat, D.K. (1975). Traffic safety on Bridges. Master’s Thesis, Concordia University
Montreal, Quebec, Canada.
3. CRC Construction Innovation, (2002). Whole of Life Cycle Cost Analysis in Bridge
Rehabilitation, MA.
4. Frank, R. “Safety First” for bridges – by design, Cardno MBK, Victoria.
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