Question

Two roadway designs are under consideration for access to a permanent suspension bridge. Design 1A will cost $1.7 million to build and $175,000 per year to maintain. Design 1B will cost $3.6 million to build and $40,000 per year to maintain. Both designs are assumed to be permanent. Use an AW-based rate of return equation to determine (a) the breakeven ROR and (b) which design is preferred at an MARR of 25% per year.

Answer 1

Answer and Explanation:

A. Given that Design 1A will cost $1.7 million to build and $175,000 per year to maintain

Given that Design 1B will cost $3.6 million to build and $40,000 per year to maintain

Both designs are assumed to be permanent

To find ROR using AW based rate of return equation, we find present value of each design and equate them:

Each design is permanent so

Present value of perpetuity:

Design 1A= 1700000+175000/r

Design 1B = 3600000+40000/r

=1700000+175000/r=3600000+40000/r

135000/r=1900000

Cross multiply

r=135000/1900000

r= 0.0710

r=7.10%

B Given that ROR=7.10% and MARR is 25%

MARR>ROR

Hence we reject both designs