PPME Subdivision Design Assignment


Economic Analysis

Prepare a spreadsheet (using EXCEL, Quattro or a similar program) that provides a financial analysis of a proposed subdivision. Include a calculation of the cost of development -- sewers + streets + grading + land + interest + soft costs. Set up the spread sheet so you can use land cost and interest rates as parameters. Use other cost data from the Notes or some other appropriate source; update these costs to the current year by 1.6% per year. Assume general characteristics of a subdivision for the purposes of setting up the spreadsheet.

Once you have determined your final project design at the end of the semester, examine the cash flow of the project over time. Assume that 25% of construction costs in year one and 75% in year two and land costs over six years. Assume one fourth of the lots are sold per year beginning with year three. Find the price per lot that is required to have a 25% return on investment. Assume an interest rate of 2 points over the prime rate. Costs and revenues for years two to six should be discounted by 1/(1+i)n.

Hand in a print of your spreadsheet, and a listing of the cell formulas used to calculate costs in the sixth year of the project on the due date in the class syllabus. Keep your disk, as you will need it for the final phase of the project.

Subdivision Layout

A parcel of land (to be designated) located in your neighborhood is to be subdivided into lots following your neighborhood plan. (If you reserved the site for all open space, you should revise your plan for residential and mixed development.) You should modify your plan if necessary.

A draft design (layout of subdivision) should be submitted for review and critique by the required date to get some feedback for the project.

Street Design

You will need to locate streets and lots in the subdivision. The street centerline will need to match the streets that enter the area. The streets will contain storm sewers (see the next part) that will flow out to connect to a nearby arterial or drainage way. Locate the street's centerline horizontally and vertically. Show your results on a subdivision plan map and on plan/profile paper. Follow WDOT design guidelines and use a horizontal scale of 1" = 50 ft. and a vertical scale of 1" = 10 ft.. Label PC, PI, PT, D, R and T for horizontal curves; PVC, PVI, PVT, L, G1, G2 for vertical curves on the drawing. Also show existing grade and proposed grades as well as elevations at every station and at beginning and ends of vertical curves. Also show a typical section. Include your calculations.

Storm Sewers

Determine pipe size and slope and location of manholes for a storm sewer system to drain the area given in the previous assignment. Assume a runoff coefficient of 0.40 and an inlet time of 10 minutes for areas with a maximum flow distance of 500 ft. or less. (Increase inlet time by 1 minute per 50' if the distance is greater than 500 ft.). Rainfall intensity can be found from the following formula (10 year storm):

I = 141.8/(17.1+t)

where t is inlet time + flow time.

The minimum cover for the sewer should be 4 feet and the minimum pipe size should be 12".

For the purposes of this assignment, assume that you will be draining only your parcel.


Reports and Drawings

Explain your designs in a brief report. Your report should include an explanation of the following (use headings): relation to neighborhood design, goals of your design, assumptions made in your design, subdivision layout, horizontal alignment of streets, vertical alignment of streets, sewer layout and design, economic analysis, conclusions.

Your drawings should include the following:

(Note plan and profile views are on same piece of paper.)

Everything (plat, plan and profile of streets and sewer, and report) is due December 13 at 4:00 p.m..