R t
ð Þ þ F t
ð Þ ¼ 1
ð9:1Þ
The reliability R(t) will decrease with time: When new, any product usually
meets all specifications, but less so after a given period. After, say 1 year, the
reliability of the product may have reduced to 0.6. Conversely, the unreliability
F(t) of the product increases with time: with the example above, the product which
satisfies the specifications À unreliability ¼ 0 À will have an increasing unreliability
with time, rising to 0.4 after 1 year.
What about the connection between quality and reliability? A reliable product
retains its quality as time elapses.
Thus, a good quality product will not only have high quality, but will also have a
high reliability over a long period. A high initial quality, only over a short period, is
practically useless.
Similarly, a low quality product may be highly reliable over a long period of time,
but the quality remains low.
To summarise, only a good quality product can be relied upon, over a long period
of time.
9.3 Importance of Quality and Reliability
9.3.1 Introduction
Most countries, nowadays, depend on electricity being available for most of their
activities. An unreliable electricity supply would lead to a major catastrophe. At the
other end, in many poor countries, infrastructure is, however, quite unreliable, in
several sectors. Frequent, irregular, electricity shortages may entail power rationing
for industry, agriculture, and domestic use; if voltage drops become significant,
equipment may burn out, not to mention the dependency of the internet on power
availability. Poorly maintained roads inhibit the transport of goods, or at least
increases their final cost. A farmer who spends much time on a road full of potholes,
will increase his cost of production (and his selling price) because of (1) the extra
time lost and (2) his vehicle also needs more repairs, with the result that competitors
may be cheaper, or consumers have to foot the bill. An unreliable water supply for
many irrigation systems encourages farmers to be reluctant about maintaining
irrigation structures and pay for the water.
9.3.2 Infrastructure Unreliability
Infrastructure studies on unreliability (Lee and Anas 1990) show that large and small
firms are affected differently. Large firms can afford to invest spend significant
260
9 Quality and Reliability of Infrastructure
ð Þ þ F t
ð Þ ¼ 1
ð9:1Þ
The reliability R(t) will decrease with time: When new, any product usually
meets all specifications, but less so after a given period. After, say 1 year, the
reliability of the product may have reduced to 0.6. Conversely, the unreliability
F(t) of the product increases with time: with the example above, the product which
satisfies the specifications À unreliability ¼ 0 À will have an increasing unreliability
with time, rising to 0.4 after 1 year.
What about the connection between quality and reliability? A reliable product
retains its quality as time elapses.
Thus, a good quality product will not only have high quality, but will also have a
high reliability over a long period. A high initial quality, only over a short period, is
practically useless.
Similarly, a low quality product may be highly reliable over a long period of time,
but the quality remains low.
To summarise, only a good quality product can be relied upon, over a long period
of time.
9.3 Importance of Quality and Reliability
9.3.1 Introduction
Most countries, nowadays, depend on electricity being available for most of their
activities. An unreliable electricity supply would lead to a major catastrophe. At the
other end, in many poor countries, infrastructure is, however, quite unreliable, in
several sectors. Frequent, irregular, electricity shortages may entail power rationing
for industry, agriculture, and domestic use; if voltage drops become significant,
equipment may burn out, not to mention the dependency of the internet on power
availability. Poorly maintained roads inhibit the transport of goods, or at least
increases their final cost. A farmer who spends much time on a road full of potholes,
will increase his cost of production (and his selling price) because of (1) the extra
time lost and (2) his vehicle also needs more repairs, with the result that competitors
may be cheaper, or consumers have to foot the bill. An unreliable water supply for
many irrigation systems encourages farmers to be reluctant about maintaining
irrigation structures and pay for the water.
9.3.2 Infrastructure Unreliability
Infrastructure studies on unreliability (Lee and Anas 1990) show that large and small
firms are affected differently. Large firms can afford to invest spend significant
260
9 Quality and Reliability of Infrastructure