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From page 9... ... 9 e DBB project delivery method is the primary method used for transportation projects in DOTs. e frequent use of this method will continue to be popular in the future because it carries many benets for the owner, such as construction cost savings driven by competitive bidding, relatively higher construction cost certainty, clearer responsibility and liability arrangements due to separation of design and construction, relatively easier management because of its linear process, tighter contract administration, and more. Read the entire page →
From page 10... ... 10 Systematic Approach for Determining Construction Contract Time: A Guidebook order to secure certainty on the completion time of major milestone work items. When setting up the contract, the agency needs to evaluate the applicability and the pros and cons of each contract time type to select the most appropriate type or types for the project. Read the entire page →
From page 11... ... CTD Guide for DBB Projects 11 amount of contract work that has critical deadlines (all or some major contract work) Read the entire page →
From page 12... ... 12 Systematic Approach for Determining Construction Contract Time: A Guidebook of calendar days (i.e., it can be moved) Read the entire page →
From page 13... ... CTD Guide for DBB Projects 13 Working day contract Calendar day contract Calendar day + working day contract Fixed completion date contract Fixed completion date + working day contract NTP window Legend: Agency has control (i.e., the parameter can be explicitly specified by the agency in the contract) Read the entire page →
From page 14... ... 14 Systematic Approach for Determining Construction Contract Time: A Guidebook In all these cases, the agency has control over the project start date (i.e., NTP date) Read the entire page →
From page 15... ... CTD Guide for DBB Projects 15 duration estimate (PDE) is dened as a rational estimate of the time needed to complete the scope of the work specied in a contract based on available project design and known project information under the assumption of normal working conditions. Read the entire page →
From page 16... ... 16 Systematic Approach for Determining Construction Contract Time: A Guidebook 2.2.3 Step 3 -- Select the Contract Time Type An important decision that the agency needs to make before determining a specic number of days or assigning a completion date for the contract is to select the type of contract time (e.g., working day, calendar day, or xed completion date) Read the entire page →
From page 17... ... CTD Guide for DBB Projects 17 2.3 CTD Procedure for DBB Projects -- Steps and Sub-Steps 2.3.1 Step 1 -- Estimate the Project Duration Various scheduling methods are available for establishing the PDE. ere are two major approaches: bottom-up and top-down (see Figure 2-5) Read the entire page →
From page 18... ... 18 Systematic Approach for Determining Construction Contract Time: A Guidebook Methods Advantages Disadvantages/Limitations Bar Charts/Gantt Charts • Simple, easy to understand • Do not show relationships between activities • Do not indicate controlling activities • Do not show the effects of changes Critical Path Method • Four types of activity relationships • Able to identify critical paths • Easily determines the effect of change orders/delays • Performs what-if analyses using different construction methods/sequences • Requires knowledge and experience from users • Deterministic method Linear Scheduling • Effective for linear and repetitive projects • Visual representation of activities with production rates • Only effective on pure linear projects • Deterministic method Program Evaluation and Review Technique (PERT) • Stochastic method • Obtains risk-appropriate project duration • Ignores all sub-critical paths • Generates optimistically biased project duration • Difficult to provide three durations for each activity Estimated Cost Method • Quick and easy estimation with a predeveloped model • Sensitive to accuracy and size of input database Multiple Regression • Good for top-down estimation with key parameters • Accuracy in question Artificial Neural Network (ANN) Read the entire page →
From page 19... ... CTD Guide for DBB Projects 19 Sub-Step 1 -- Select a scheduling method for PDE. • When multiple scheduling methods are available and allowed for establishing the PDE, it is necessary to have proper guidance on how to choose an appropriate scheduling method for a given project. Read the entire page →
From page 20... ... 20 Systematic Approach for Determining Construction Contract Time: A Guidebook e bottom-up approach commonly involves the sub-steps shown in Figure 2-8: List activities and their corresponding quantities Estimate project duration using bar chart or CPM Establish project specific production rates Establish construction logic Calculate duration for each activity Estimate project duration using the selected method [Bottom-up Method] Sub-Step 2e -- Estimate project duration using bar chart or CPM. Read the entire page →
From page 21... ... CTD Guide for DBB Projects 21 Review the tool and its user manual Provide input for the tool Generate project duration Estimate project duration using the selected method [Top-Down Method] Sub-Step 2a -- Review the tool and its user manual. Read the entire page →
From page 22... ... 22 Systematic Approach for Determining Construction Contract Time: A Guidebook The outcome of this step. A project duration estimate (PDE) Read the entire page →
From page 23... ... CTD Guide for DBB Projects 23 2.3.2 Step 2 -- Determine Milestone and Completion Date Constraints e estimated project duration obtained in Step 1 can dier from the nal contract time due to the existence and inuence of non-technical and external factors (e.g., weather and seasonal eects, coordination with other projects, and political commitments) that can impose constraints on the milestones or the completion date of a project. Read the entire page →
From page 24... ... 24 Systematic Approach for Determining Construction Contract Time: A Guidebook Required documents and information. State regulations, federal or state agency guidelines, state 5-year programs, standards specifications, CTD manuals, project requirements, design plans, and others (e.g., agreements with local officials) Read the entire page →
From page 25... ... CTD Guide for DBB Projects 25 Tool T2.4 (described in Appendix A and accessible in the downloadable CTD4HP Toolkit) addresses 42 inuential factors and their potential impacts on contract time. Read the entire page →
From page 26... ... 26 Systematic Approach for Determining Construction Contract Time: A Guidebook 2.3.3 Step 3 -- Select the Contract Time Type Four pieces of information are necessary to make an informed and accurate decision about selecting the type of contract time: 1. Milestone and completion date constraints, 2. Read the entire page →
From page 27... ... CTD Guide for DBB Projects 27 Step 3 Select Contract Time Type Figure 2-14 provides an overview that summarizes Step 3. Tool T2.5 is described further in Appendix A and is accessible via the downloadable CTD4HP Toolkit. Read the entire page →
From page 28... ... 28 Systematic Approach for Determining Construction Contract Time: A Guidebook 2.3.4 Step 4 -- Convert Working Days to Calendar Days If the selected contract time type in Step 3 is calendar day or xed completion date, it will be necessary to convert working days to calendar days to compare the PDE (obtained in Step 1) with the milestone and completion date constraints (obtained in Step 2) Read the entire page →
From page 29... ... CTD Guide for DBB Projects 29 Figure 2-16. Integrated working calendars. Read the entire page →
From page 30... ... 30 Systematic Approach for Determining Construction Contract Time: A Guidebook Table 2-6 provides examples of two environmental calendars: water access calendars from the Massachusetts DOT and an in-stream construction calendar from the Virginia DOT. Specic activities (e.g., pile driving, coerdams, dredging) Read the entire page →
From page 31... ... CTD Guide for DBB Projects 31 Step 4 Convert to Calendar Days The outcome of this step. An integrated working calendar, including (a) Read the entire page →
From page 32... ... 32 Systematic Approach for Determining Construction Contract Time: A Guidebook 2.3.5 Step 5 -- Determine Contract Time is step determines a PDE-based contract time and a constraint-based contract time and compares the two to determine the contract time for letting. Figure 2-18 presents the sub-steps of the procedure and Figure 2-19 provides an overview that summarizes Step 5. Read the entire page →
From page 33... ... CTD Guide for DBB Projects 33 Required documents and information. The project duration estimate in working days (obtained from Step 1) Read the entire page →
From page 34... ... 34 Systematic Approach for Determining Construction Contract Time: A Guidebook 2.4 Impacts of Advanced Technologies on Project Duration is section provides general guidance on the impacts of some increasingly adopted advanced technologies on project duration and the methods of taking into account those impacts when estimating project duration. 2.4.1 Advanced Technologies and Their Impact on Project Duration Increasingly, DOTs are using advanced technologies to improve project performances such as cost, time, quality, and safety. Read the entire page →
From page 35... ... CTD Guide for DBB Projects 35 – Vibratory rollers are equipped with GPS devices, a measurement system of the deformation of materials during compaction, temperature trackers, and a reporting system to track roller movements, materials temperature, roller passes, and compaction measurements (Chang 2017, Patel et al. Read the entire page →
From page 36... ... 36 Systematic Approach for Determining Construction Contract Time: A Guidebook those models by adding advanced technologies as input variables. However, the number of projects using the technologies should be large enough to ensure the accuracy of the estimation models. Read the entire page →
From page 37... ... CTD Guide for DBB Projects 37 2.5.1 Step 1 -- Identify Potential Input Variables Each factor that aects project duration can be taken into consideration by incorporating an input variable that represents the factor. In the context of highway construction, examples of input variables include project cost, roadway length, and the number of lanes. Read the entire page →
From page 38... ... 38 Systematic Approach for Determining Construction Contract Time: A Guidebook Chang, G Read the entire page →

From page 9...

... 9 e DBB project delivery method is the primary method used for transportation projects in DOTs. e frequent use of this method will continue to be popular in the future because it carries many benets for the owner, such as construction cost savings driven by competitive bidding, relatively higher construction cost certainty, clearer responsibility and liability arrangements due to separation of design and construction, relatively easier management because of its linear process, tighter contract administration, and more.