Civil Engineering Reference
In-Depth Information
Small variations in vehicle manufacturing can cause fuel economy variations in
the same make and model,
Some vehicles do not attain maximum fuel economy until they are
“
broken in
”
(around 3,000
5,000 miles).
-
An extra 100 lbs. can decrease fuel economy by 1
2%.
-
A roof rack or carrier provides additional cargo space and may allow one to
meet one
s needs with a smaller car. However, a loaded roof rack can decrease
fuel economy by 5 %.
'
Factors in
fl
uencing fuel economy include:
Observing the speed limit: each 5 mph one drives over 60 mph can reduce your
fuel economy by 7
8%.
-
Idling gets 0 miles per gallon and costs as much as $0.04 per minute.
Using cruise control on the highway to help maintain a constant speed usually
will save gas.
A car that is noticeably out of tune can decrease gas mileage by about 4 %.
Keeping tires in
ated to the recommended pressure and using the recommended
grade of motor oil can improve fuel economy by up to 5 %.
fl
Replacing a clogged air
filter can improve gas mileage on older cars with
carbureted engines.
Figure
13.2
shows the average relationship between fuel economy and speed
[
21
]. The higher fuel economy occurs when speeds range from about 35
55 mph.
The lowest fuel economy occurs when speeds are less than 15 mph. Thus traf
-
c
congestion has an adverse effect on fuel economy.
Excessive idling, accelerating, and breaking in stop-and-go traf
c (average speed
of 5 mph) increases fuel consumption by over 3 times the amount consumed at
highway speed is 45 and 55 mph, and by 2 times the amount consumed at 15 mph
on city streets. Table
13.6
illustrates the incremental fuel consumed at slow speeds
compared to higher speeds using data extrapolated from Fig.
13.2
.
Fig. 13.2
Fuel economy
versus speed.
Source
Reference [
21
], p 42
