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OCR for page 32
32
Upper benefit
cutoff value
Friction number
Overall post-treatment
AREA
Do nothing curve
PT(FRICTION) analysis life of 20 years
Lower benefit
cutoff value
5 10 15 20 25
Age, years
Upper benefit cutoff
value
Rutting
Do PT(RUTTING)
AREA nothing curve
Overall post-treatment
analysis life of 20 years
(associated with friction)
Lower benefit cutoff
value set to zero
5 10 15 20 25
Age, years
Upper benefit
cutoff value
International Roughness
Index (IRI)
AREAPT(ROUGHNESS) Overall post-treatment
Do nothing curve
analysis life of 20 years
(associated with friction)
Lower benefit
cutoff value
5 10 15 20 25
Age, years
Figure 8. Illustration of the total areas associated with individual condition
indicators.
friction, rutting, and IRI are 10, 16, and 20 percent, respec- lated for each individual condition indicator. In this example,
tively (i.e., when compared with the respective areas associ- the total overall benefit contribution is 14.0 percent. While by
ated with the do-nothing option, the preventive maintenance itself this actual total benefit value is essentially meaningless,
treatment application results in increases of 10, 16, and 20 per- total benefit values computed for different timing scenarios can
cent in the friction, rutting, and IRI areas, respectively). Fur- be used to compare the effectiveness of the different timing
ther assume benefit weighting factors of 50, 25, and 25 are scenarios. Results of this example are presented in Table 19.
chosen for friction, rutting, and IRI, respectively (note that
these factors add up to 100). The overall benefit contributions
are then determined by multiplying the benefit weighting fac- Step 9: Cost Computations
tor percentages by the individual benefit values (e.g., for fric-
tion 10 percent × 50/100 = 5.0 percent). The total overall benefit A simple two-step LCCA is conducted to compare the dif-
contribution is then computed as the sum of the values calcu- ferent cost streams associated with each preventive mainte-
