Benefits and Challenges of Design-Build - Design-Build for Water and Wastewater Projects - page 12

Table 2-1. Comparison of schedule performance by delivery method for building and
transportation projects

Item

CII/Pennsylvania State
University Study*

University of
Reading Study†

FHWA Report
to Congress‡

Construction Speed DB 12% faster than

DBB

DB 12% faster than
DBB

—

Total Speed of Project
Delivery

DB 33.5% faster than
DBB

DB 30% faster than
DBB

DB 14% faster
than DBB

* Konchar and Sanvido 1998, Sanvido and Konchar 1999
† Bennett, Pothecary, and Robinson 1996
‡ FHWA 2006

Table 2-2. Comparison of schedule performance by delivery method for design and
construction of water and wastewater facilities (median values) (Bogus,
Shane, and Molenaar 2009)
Performance Measure Design-Build Design-Bid-Build

Schedule Duration (months) * 23 40

Schedule Growth (months) * 1.0 2.0

Proportion of Projects with Schedule Growth ≤0* 41% 36%

* Statistically significant results
Source: Bogus, Shane, and Molenaar 2009.

Cost

Design-build can also provide benefits in terms of cost savings. The cost savings can come
from many areas including design and construction innovations, fewer change orders,
improved communication, shorter project schedules, and reduced claims. For building
projects, DB was found to have lower project or unit costs of between 6 and 13 percent
(Table 2-3). For transportation projects, DB was found to reduce the total project cost by
3 percent (Table 2-3). Design-build projects also were more likely to be completed within
5 percent of the project budget compared to DBB projects. In a study specific to water
and wastewater facility projects, DB projects had lower cost growth and were significantly
more likely to finish within budget, even while the total project size was generally larger
(Table 2-4).
The mechanisms by which DB projects can achieve cost savings are not as clearly
defined as they are for schedule savings. In terms of schedule, time savings can clearly
be achieved by eliminating the contractor's bid phase in DBB and overlapping design
and construction in DB. For costs, there are many areas where savings can be achieved,
although actual DB performance is more variable in terms of cost benefits than it is in
terms of schedule benefits.