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Systematic Approach for Determining Construction Contract Time: A Guidebook (2022)

Chapter: Chapter 2 - CTD Guide for DBB Projects

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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
×
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Suggested Citation:"Chapter 2 - CTD Guide for DBB Projects." National Academies of Sciences, Engineering, and Medicine. 2022. Systematic Approach for Determining Construction Contract Time: A Guidebook. Washington, DC: The National Academies Press. doi: 10.17226/26537.
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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. Due to its structural separation of construction from design, construction contract time in a typical DBB project is determined at the end of the nal design, or the PS&E stage (see Figure 2-1). In most DOTs, the estimated contract time is a required line item in PS&E docu- ments. At this stage, the project design is about 90 to 95 percent complete, and most project information is available. However, setting the construction contract time is a challenging process. A contract time developer needs to possess expertise and competence in understanding the work scope, analyzing required work activities, and visualizing how the project is likely to be constructed. CTD is much more than estimating the technically required duration of a project. e contractually allowable time or its range for a transportation project may be driven by many other constraints, such as political commitment, funding availability, environmental constraints, neighboring projects, labor market conditions, and community events, to name a few. us, a contract time developer must also be able to identify and comprehensively evaluate all of those potential internal and external factors that may aect contract time and carefully incor- porate them into determining the contract time. is chapter provides a procedural guide on CTD for a conventional DBB project. It rst pro- vides guidance on dierent types of contract time. en, a generic procedure is presented with detailed descriptions for each step and component in the procedure. 2.1 Types of Contract Time e types of contract time (e.g., working day or calendar day) aect the procedures used to determine contract time. For example, determining the contract time of a single-season working day contract may not require a thorough analysis of non-working days during construction (e.g., holidays and winter shutdown periods) because the non-working days do not aect the contract time. 2.1.1 Three Fundamental Types of Contract Time In general, three fundamental types of contract time must be considered: (1) working day, (2) calendar day, and (3) completion date. Some contracts may include more than one type of contract time (e.g., working day + calendar day, or xed completion date + working day) in C H A P T E R   2 CTD Guide for DBB Projects

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. Working Day Working day contract time reects only the days available to perform the work. For calcula- tions of working day contract time, every day is shown on the calendar with the exception of the following: • Saturdays, Sundays, and state-recognized holidays; • Days on which the contractor is specically required by the contract to suspend operation (e.g., winter shutdown period); and • Any other days that have been determined by the agency to be non-working days, such as those caused by: – Weather conditions that do not permit work to be eectively performed for a specied amount of time, or – Delays beyond the contractor’s control. e exceptions above are collectively known as non-working days. e agency has the nal authority to decide whether each day is charged as a working day or not. For example, a typical working-day week will have 5 days (Monday, Tuesday, Wednesday, ursday, and Friday), but in a given week the agency may only charge the contractor 4 working days because a community event that is scheduled to occur on one of the 5 days is signicant enough for the agency to charge it as a non-working day. When working day contract time will be used, to minimize disputes and claims with the contractor the agency should include in the contract a detailed guideline on charging working days. Calendar Day For calendar day contract time, every day is shown on the calendar. Each calendar day begins at midnight and extends for 24 hours, ending at midnight (the beginning of the next calendar day). A calendar day includes weekends and state-recognized holidays. e number of calendar days are tracked, but the days are not assessed as chargeable or non-chargeable because calendar day contract time does not depend on the amount of work performed by the contractor on any given day. at is, the number of calendar days is tracked, but the days are not assessed as chargeable or non-chargeable. Fixed Completion Date A xed completion date is a specic calendar date that is mentioned in the contract and by which date the work (or a specied portion of the work) will be completed. 2.1.2 Criteria for Determining Type of Contract Time e type of contract time can be determined by the criticality of project completion (e.g., whether the work is to be completed within a specic timeframe or by a specic date) or the Planning/ Programming Preliminary Design Final Design Advertise & Award Construction Contract Time Determination (90%–95% Plan) Figure 2-1. Timing of CTD.

CTD Guide for DBB Projects 11   amount of contract work that has critical deadlines (all or some major contract work). Highway agencies can apply any of the fundamental contract time types or combine two or more types of contract time by applying them to dierent parts of work in the same contract. Table 2-1 summarizes the denitions and applicability of each contract time type, and Table 2-2 shows the benets and weaknesses of each contract time type to support highway agencies in making the decision. Figure 2-2 further illustrates the dierences between each type of contract time. Only the xed date contract can contractually guarantee the completion date of a project. e ultimate end date of a project is not known when other types of contract time are used. e notice to proceed (NTP) released by the agency may aect the completion date of a project in all types of contract time except for the xed date contract. Using working day contract time, the agency controls the contract time of a project by specifying the number of allowable working days. A delayed NTP will not erode contract time, or the time allocated for the contractor to complete the job because the contract time is specied in a time- frame (i.e., number of working days) and not set by a specic date. However, because there is uncertainty involved in the number of non-working days (e.g., weather delays), the ultimate project completion date cannot be identied directly. Using calendar day contract time, the agency controls the contract time by specifying the number of calendar days. Although the ultimate project completion date is known, it is not xed to a specic calendar date. Instead, it is determined based on the NTP date as well as the number Contract Time Type Definition(What the Contract Specifies) Applicability Working day  The number of working days it should take for the contractor to complete the work  When the project completion date is not critical  Single construction season projects Calendar day  The number of calendar days to establish the completion date based on when the contract is started  When the contract work is to be completed in a specific timeframe Calendar day + Working day  The number of calendar days to establish the completion date for a portion of work based on when the contract is started and  The number of working days to complete any remaining (typically miscellaneous) work  When a facility must be open in a specific timeframe, but not all work has to be completed by the completion date  When miscellaneous items in the contract are weather-sensitive or require performance or establishment periods (e.g., landscaping and pavement markings) Fixed completion date  The date when the work is to be completed  When all project work must be completed by a specific date Fixed completion date + Working day  The date that some portion of work must be completed and  The number of working days to complete the remaining work (typically miscellaneous items)  When a facility or part of the facility must be open by a specific date but not all work has to be completed by the completion date  When miscellaneous items in the contract are weather-sensitive or require performance or establishment periods (e.g., landscaping and pavement markings) Contract time set by contractor  Contract time (e.g., fixed completion date or number of calendar days) proposed by the awarded contractor becomes the new contract time  Represents the “B” portion if the contract is procured using A+B bidding mechanism  A+B projects in which construction acceleration is desired Table 2-1. Denition and applicability of each type of contract time.

12 Systematic Approach for Determining Construction Contract Time: A Guidebook of calendar days (i.e., it can be moved). Because calendar day contracts do not dierentiate weekends, holidays, weather days (unless otherwise specied in the contract), and so forth, the contractor bears more schedule risk than in a working day contract. Using calendar day + working day contract time, the entire project is divided into two phases based on the schedule criticality of work items. For work items that are critical (schedule- wise), an agency can control the completion of these work items by specifying a timeframe (i.e., number of calendar days). e interim completion date (for critical work items) is then determined based on the NTP date and the number of calendar days. e remaining work items are administered like a working day contract. Because of the uncertainties involved in the number of non-working days, the ultimate completion date cannot be determined directly. Using a xed completion date contract, the agency controls the contract time by specifying a completion date. In other words, the ultimate completion of the project is known and is tied to a specic calendar date (i.e., cannot be moved). Because the contract time is not administered as a timeframe, a delayed NTP will certainly erode the initial duration allocated for the contractor to complete the job. us, the contractor bears most of the schedule risk in this type of contract. Using the xed completion date + working day contract time approach is very similar to using a calendar day + working day contract, with one exception: In this type of contract, the agency controls the contract time for critical work items by specifying a xed completion date for each critical item instead of specifying a timeframe. is approach means that the interim completion dates are known and do not change, regardless of the NTP date. e use of working day contract time for the miscellaneous phase of the project also suggests that the ultimate completion date cannot be identied directly. Contract Type Benefits Weaknesses Working day v Agency can delay start without penalty to contractor v No specified date for completion v Charging working days can be subjective (i.e., difficult) Calendar day v Flexible completion date (established based on start date) v Prevents contractor from prolonging the work over more than one season v Possible conflicts due to potential time requests Calendar day + Working day v Flexible completion date (established based on start date) v Prevents contractor from prolonging the work over more than one season v Specifies a date when the major items of work must be completed v Working days allows time for miscellaneous work to be completed after the completion date v Possible conflicts due to potential time requests Fixed completion date v Prevents contractor from prolonging the work v Specifies a date when all work must be completed v Possible conflicts due to potential time requests v Project completion potentially delayed if there is any delay between letting and notice to proceed (NTP) Fixed completion date + Working day v Specifies a date when the major items of work must be completed v Working days allow time for miscellaneous work to be completed after the completion date v Possible conflicts due to potential time requests v Project completion potentially delayed if there is any delay between letting and NTP Contract time set by contractor v Potentially results in tighter schedule v Possible conflicts due to potential time requests v May cause schedule-related disputes and claims Table 2-2. Benets and weaknesses of each type of contract time.

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). Figure 2-2. Comparing types of contract time.

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). Contract time will begin to be assessed as soon as the NTP is issued, regardless of the contractor’s avail- ability. However, the agency can introduce exibility in the contract time by specifying an NTP window. An NTP window means that the agency has established both the earliest and latest permissible start dates, but it is up to the contractor to decide when to actually commence work on the project within that window. is type of provision is usually paired with a working day contract or a completion date (via a calendar day) contract. In both cases, the agency maintains its control over the allowable timeframe of the project. However, because the ultimate project completion date is tied to the project start date—which is chosen by the contractor—it will not be directly known by the agency at the time of project procurement. Some agencies, such as the North Carolina DOT, have used this contracting technique, and it has increased the bidding competition and possibly lowered the bid prices. 2.1.3 Special Provisions to Introduce Flexibility into Contract Time In addition to the type of contract time, special provisions may be added into the contract to provide exibility in contract time (see Table 2-3). 2.2 Generic CTD Procedure for DBB Projects Contract time is the maximum time allowed in the contract for completion of all work con- tained in the contract documents (FHWA 2002). Project duration is commonly used interchange- ably with contract time in practice, but this guidebook denes each one dierently. Project Special Provision Description Conditional NTP v Conditional NTP is also known as delayed start date. v The contract specifies a period for fabrication and delivery, as well as the number of working days allowed for construction. v Time charges begin at the end of fabrication and delivery period. v This provision is used when the contract time is expected to be controlled by long lead-time of certain project items (e.g., lighting and signal equipment, fabricated steel members). NTP window v The contractor is allowed to commence work at any time within a specified timeframe (i.e., flexible start date). v Once work has started, the contractor will then have to complete the work within the number of working days/calendar days specified in the contract. v The NTP window is established by specifying the earliest and the latest permissible start date that a contractor can commence work. v Benefits of this provision: i. It allows contractor flexibility in scheduling projects and work crews; ii. Through the use of an allowable number of working/calendar days, it still limits the contractor’s on-site time (which means the traffic disruption will be limited as well); and iii. It increases the probability of competitive bids (more contractors are able to bid the contract without the restrictive start date). v Applicability—This provision is best applied when: i. The ultimate completion date is not critical; ii. A large number of projects involving specialized work (e.g., seal coats, highway planting, pavement grooving or bridge painting) are being advertised within a short period of time; iii. Projects have a very limited number of working days; and iv. Minor projects (e.g., resurfacing, guardrail, and bridge deck overlays) are required. Table 2-3. Provisions for exible contract time.

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. us, PDE generally ignores non-technical factors and external constraints. e PDE is used as a basis for estimating contract time. However, the PDE does not necessarily equal the contract time. Non-technical and external factors (e.g., political commitments) may eventually dictate the contract time, which is typically shorter than the original PDE. e two main determinants for contract time are (a) a PDE when no external constraints are considered, and (b) external-factor-driven milestones and completion date constraints. CTD is a result of the dynamic interaction between the two, and a series of back-and-forth adjustments between both the PDE and major milestones and completion date constraints may be required to determine the most reasonable and acceptable contract time (see Figure 2-3). e agreement of PDE and those external constraints will result in the contract time. For example, a project may need to be completed before the start of the winter season or before a special community event. However, it is important that the agency estimates project duration using a scheduling method and compares it with both the milestones and the required completion date constraints. e comparison is made to ensure that the established time is realistic for contractors to complete the job and does not give the contractors excessive time, which may cause unnecessary disruptions to the public (ITD 2011). A comparison between the PDE-based contract time and the constraint-based contract time (i.e., milestones and completion date constraints) provides the agency with the level of acceleration needed for the project based on the magnitude of the dierence between the two contract time estimates. A generic ve-step procedure can be used for determining contract time. e ve steps are described in the balance of this section and summarized in Figure 2-4. 2.2.1 Step 1—Estimate the Project Duration (in Working Days) If a project is let as a working day contract, a PDE is needed to determine the number of working days. If a project is let as a calendar day or completion date contract, the PDE is still necessary to ensure that the established contract time is realistic without signicant acceleration. e two major approaches for establishing a PDE are as follows: (a) the production rate-based approach (e.g., bar charts and critical path method [CPM]), and (b) the project parameter-based approach (e.g., the estimated cost method, multiple linear regression, and articial neural networks). 2.2.2 Step 2—Determine Milestone and Completion Date Constraints For any given project, it is important that the agency checks for and identies any milestone and completion date constraints. Typically, these types of constraints are imposed by non- technical factors (e.g., environmental issues, the urgency of completion, political commitment, weather and seasonal eects, special events, and coordination with other projects). Figure 2-3. Two main determinants for contract time.

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). e results from Steps 1 and 2, an anticipated letting date, and some other criteria (e.g., the impact of the project on the traveling public and businesses) are used as input for Step 3. If working day is selected as the type of contract time, the PDE in working days is likely to become the nal contract time, and the CTD process is nished. Otherwise, Steps 4 and 5 need to be taken. 2.2.4 Step 4—Convert Working Days to Calendar Days is step converts the estimated project duration in working days in Step 1 to calendar days based on the anticipated letting date and non-work constraints on contract time. Some examples of non-work constraints are holidays, winter shutdown periods, and limited allowable working windows of some activities due to specication requirements and environmental restrictions. 2.2.5 Step 5—Determine Contract Time is step compares the PDE-based contract time in calendar days calculated in Step 4 to the constraint-based contract time based on the milestones and completion date constraints identied in Step 2. e two contract times are evaluated and adjusted to determine the nal contract time. Estimate Project Duration Bottom-up Scheduling Methods Top-down Scheduling MethodsST EP 1 Determine Constraints Factors That May Dictate Contract Time Relevant Documents & StakeholdersST EP 2 Select Contract Time Type Required Completion Date Impact on Traffic & BusinessesST EP 3 Convert to Calendar Days Typical Working Calendar Non-working Days ST EP 4 Determine Contract Time PDE-based Contract Time Constraint- based Contract TimeST EP 5 Procedures Influential Factors/Major Components/Options Figure 2-4. Overall CTD procedure for traditional DBB projects.

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). e bottom-up approach, like CPM, requires detailed information on construction activities, such as quantities, production rates, and sequential relationships between the activities, to establish a construction schedule, which provides the project duration. e top-down approach, like multiple linear regression, relies on a predeveloped model that captures the relationships between general project characteristics and project duration in past projects to predict the project duration of a new project. At the end of the nal design phase, the bottom-up approach is preferred over the top-down approach for the following reasons: 1. Bottom-up methods can leverage the available detailed project information, such as design plans and trac maintenance plans. In contrast, the top-down methods only consider some general project characteristics as input to predict project duration. 2. Current top-down prediction models cannot consider the eects of various inuential factors on project duration. Some examples are environmental issues, work area restrictions, coor- dination with and relocation of utilities for construction, and working time restrictions. is limitation makes the accuracy of the top-down approach questionable. is step starts with the selection of a scheduling method used for the PDE. Next, the selected method is used to estimate the project duration in working days. Figure 2-6 presents three levels of detail that can be used when considering scheduling methods. Table 2-4 summarizes the advantages and disadvantages of potential scheduling methods to support the selection, and Figures 2-7 through 2-10 present the specic tasks (sub-steps) that are completed to execute Step 1. In this guidebook, Appendix A provides more detailed information about specic sched- uling methods in relation to Tool T2.1. Access to Tool T2.1 is provided in the downloadable CTD4HP Toolkit. Step 1 Estimate Project Duration Bottom-up approach Top-down approach Scheduling methods Project parameters Prediction models (e.g., multiple regression) Production rates Activity logic Others Activities & Quantities Project duration Figure 2-5. Two major approaches for establishing the PDE.

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) • Able to learn both linear and non-linear relationships between variables • Develops solution quickly • Accuracy depends on the quality and amount of training data • Difficulties in the selection of the most appropriate size and configuration of a network Case-Based Reasoning (CBR) • Utilizes specific knowledge from similar cases to develop solution • Considerable effort needed to construct a CBR system • Solutions lack creativity Monte Carlo Simulations • Probabilistic method • Less likely to under- or over- estimate a schedule (compared to PERT) • Need to identify statistical distribution for each simulation input • Need to recognize and determine correlation and interdependency between variables Table 2-4. Advantages and disadvantages of scheduling methods. Step 1 Estimate Project Duration No CriteriaDetailLevel 1 Guidance. A scheduling method is required for all projects. In this case, CPM is recommended, as it is more generic than the bar chart method. Example. A DOT can use CPM as a standard method for all projects. One CriterionDetailLevel 2 Criterion 1 Guidance. Use a primary criterion (e.g., project amount) to categorize projects. CPM is recommended for more complex categories. The bar chart method is used for simpler projects. Example. Bar charts for projects under $1 million and CPM for projects higher than $1 million. Multiple CriteriaDetailLevel 3 Criterion 1 Criterion 2 Guidance. Use at least two primary criteria to categorize projects. CPM is recommended for more complex categories. Example. Use CPM for urban projects over $10 million. Figure 2-6. Detail levels of a category system for scheduling methods.

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. A general approach is to categorize projects into groups based on their scheduling complexity and the required accuracy. Some criteria for evaluating scheduling complexity may include the number of work items, the complexity of the relationships among the work items, and the complexity of phasing plans. This figure provides guidance on categorizing projects for scheduling methods. • Generally, bar charts are appropriate with the projects that have low scheduling complexity, and CPM is used for projects with high scheduling complexity. Top-down scheduling methods (e.g., the estimated cost method) can be used for the projects that do not require a highly accurate PDE or can be used as a complement to the bottom-up methods. Select a scheduling method for PDE Estimate project duration using the selected method Sub-Step 2—Estimate project duration using the selected method. • Two methods can be used to estimate the project duration: Bottom-up methods (see Figure 2-8). • Top-down methods (see Figure 2-9). Figure 2-7. Step 1—Estimating project duration (step and sub-steps). Step 1 Estimate Project Duration

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. This step can be conducted using supporting tools developed by DOTs or commercial CPM software programs. Sub-Step 2b—Establish project-specific production rates. • Production rates (PRs) used for estimating project duration should be project-specific and realistically achievable by contractors. • See Appendix A (Tool T2.2) for DOTs’ production rate (PR) tables, charts, and estimation tools. • See Appendix A (Tool T2.3) for a generic tool for PR. Sub-Step 2d—Establish construction logic. Two approaches for developing the construction activity logic for a new project are (a) project-specific and (b) predefined. With the project-specific approach, schedulers start from scratch to identify activity relationships. Predefined logic templates provide schedulers with common sequences to work with in order to facilitate the process. Sub-Step 2c—Calculate duration for each activity. For a work item with quantity, the duration of the item is calculated by dividing the given quantity by the production rate estimated in the previous step. Sub-Step 2a—List activities and their corresponding quantities. • List critical activities that are necessary to complete a project. • Consider other time-consuming activities such as required submittals, time to obtain permits, and approvals of test materials. Figure 2-8. Estimating the project duration for Step 1 in working days using a bottom-up method. Step 1 Estimate Project Duration

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. Before using any tool, estimators need to know how to use the tool, its required input, the expected accuracy of the output, and the assumptions and limitations of the tool. Sub-Step 2c—Generate project duration. Given the input, the tool can immediately generate project duration. Sub-Step 2b—Provide input for the tool. • Gather relevant information and provide input for the tool by choosing among available options (e.g., less than $1 million or greater than $1 million) or by typing required values (e.g., quantities of major activities). • For example, the Colorado DOT is currently developing a neural network tool for calculating the PDE. To use the tool for a new project, a user chooses project size and project type and then types in engineer’s estimates and quantities of major bid items. Figure 2-9. Estimating the project duration for Step 1 in working days using a top-down method. The development of a top-down model is time-consuming and requires particular expertise, such as data mining, machine learning, and statistics. As a result, the model is not typically developed in-house but rather by outsourcing. After the model is developed, contract time developers can quickly estimate the project duration of a project by providing the input variables of the predeveloped model. Typical steps of using such a model for estimating project duration are shown in Figure 2-9: Step 1 Estimate Project Duration

22 Systematic Approach for Determining Construction Contract Time: A Guidebook The outcome of this step. A project duration estimate (PDE) in working days. Pros and cons. Not applicable. The methods and tools used in this step. Bottom-up methods: Spreadsheet-based tools (e.g., Tool T2.3) or commercial scheduling software programs (see Appendix A). Top-down methods: Tools developed by the agency. Emerging technology. Examples of advanced scheduling methods: Multiple linear regression, artificial neural networks, and case-based reasoning. Required documents and information. Design plans, specifications, agencies’ guidance and manuals (such as CTD manuals), and a list of bid items and corresponding quantities. Bottom-up methods: Traffic maintenance plans, records of similar past projects, specific method statements of work items from similar projects, construction industry- standard production rates (PRs) such as RS Means Heavy Construction Cost data book, and PR tables, charts, or estimation tools. Figure 2-10. Overview of Step 1—Estimate project duration. Figure 2-10 provides an overview that summarizes Step 1, the key input needed to execute the step and sub-steps, the output expected, the methods applied to complete this step, the pros and cons, and emerging technology that may be helpful in completing the step. Tool T2.1 is a spreadsheet-based generic tool for PR estimation. Tool T2.1 is further described in Appendix A of this guidebook and can be accessed via the downloadable CTD4HP Toolkit. Step 1 Estimate Project Duration

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. For example, DOTs with a harsh winter can regulate dierent completion date constraints on projects of varying work types and regions depending on the eect of the winter on construction activities. Figure 2-11 shows the sub-steps of a systematic procedure that can help determine the milestone and com- pletion date constraints. Sub-Step 1—List factors that dictate contract time. List potential factors that can control contract time. Of the factors that influence contract time, some factors can impose milestone and completion date constraints on contract time or require the adjustment of PDE to meet the constraints (see Appendix A, Tool T2.4). Table 2-5 provides descriptions and examples of the major factors that can dictate the contract time of a project. Sub-Step 2—Identify relevant documents and stakeholders. Identify relevant documents and stakeholders for each factor. For example: • Seasonal limitations of work activities can be found in standard specifications. • Political commitments can be found in agreements with local officials. • Local events can be determined by consulting with the design project managers, office of public affairs, or local officials. Sub-Step 3—Identify time constraints for each factor. Determine time constraints associated with each influential factor according to the relevant sources. Sub-Step 4—Determine project milestones and completion date. Project the constraints identified in the preceding sub-step in the same timeline and synthesize them to establish project milestones and completion date. Identify relevant documents and stakeholders List factors that dictate contract time Identify time constraints for each factor Determine project completion date & milestones Figure 2-11. Step 2—Determine constraints (step and sub-steps). Step 2 Determine Constraints

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). Examples: See Table 2-5. The outcome of this step. Possible milestones and completion date constraints. Example: A project needs to be finished by October 15 to avoid the winter season. Some projects need to be completed before a specific date to allow for the start of construction on their subsequent projects. Tourism is also considered a major event that can dictate the ending date of a project. Pros and cons. Not applicable. The methods and tools used in this step. Can be done manually or by using a spreadsheet-based tool like Tool T2.5 (see Appendix A). Emerging technology. Not applicable. Figure 2-12. Overview of Step 2—Determine constraints. Figure 2-12 provides an overview that summarizes Step 2. A spreadsheet-based tool like Tool T2.5 can be used to project and synthesize time constraints. Tool T2.5 is described further in Appendix A and can be accessed in the downloadable CTD4HP Toolkit. Step 2 Determine Constraints

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. is tool can be used eectively by the contract time developer to ensure a complete review of inuential factors. Table 2-5 provides descriptions and examples for ve major factors that inuence contract time. Influential Factor Description Examples Weather and seasonal effects Working in the winter is typically “less productive, more expensive, and more disruptive to the traveling public” (Illinois DOT 2017). Given seasonal effects, many DOTs prefer to minimize construction work in the winter months. • The Illinois DOT prefers to complete small resurfacing projects before winter (Illinois DOT 2017). • The Missouri DOT sets time limits for several types of projects (e.g., surfacing and paving projects) at the end of the construction season (Missouri DOT 2004). • In Minnesota, contract time in many cases is decided based on the weather constraints due to the short construction season in their state, and the contractors are required to speed up their operations to complete the projects as required. Coordination with other projects Coordination with other projects can also establish the completion date of a project. Some projects need to be completed before a specific date to allow for the start of construction on their subsequent projects; otherwise, claims for delays may arise (Missouri DOT 2004). • In Massachusetts, certain projects need to be postponed until other adjacent projects in the vicinity are completed to satisfy the traffic management requirements of the area. Political commitments Another major factor is political commitments, such as a request from an affected city asking a DOT to finish a project by a specific date due to a local event. • In a past project, a DOT changed design plans due to a request by a developer of a giant mall that was under construction nearby at that time. The developer requested a new exit off the highway to the mall. The agency then designed a brand-new interchange with a new bridge and ramps just for the mall. The developer also put up a million dollar bonus as an incentive to encourage the contractor to finish the project by the mall opening date. School, business, or community events Some examples of events that can dictate the completion date are tourism, state fairs, farming operations, school start and end dates (Illinois DOT 2017). • Tourism is also considered a major event that can dictate the end date of a project (Arizona DOT 2015). The increase in traffic volume in the tourist season causes a significant decrease in contractors’ productivity. Inversely, construction can negatively affect visitors. Therefore, project completion dates may be set before the tourist season, if possible, to prevent the negative influences on both sides (Arizona DOT 2015). Budget Most DOTs have a 5-year program that outlines the agency’s plan to improve the state’s transportation system, and one of the agency’s main goals is the • CTD is driven by the 5-year program in some agencies. The program specifies the number of projects that need to be completed in each fiscal year and the corresponding allocated funding. completion of the program as planned (Illinois DOT 2017). Therefore, a project should be finished before the end of its planned fiscal year. Table 2-5. Five major factors that inuence contract time. Step 2 Determine Constraints

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. e PDE in working days, 3. e anticipated letting date, and 4. Other relevant criteria, such as the criticality of the project. If working days is selected as the type of contract time, the PDE in working days (obtained from Step 1) will likely become the nal contract time. In this case, Steps 4 and 5 are not neces- sary, and the CTD process is complete. If working days is not selected as the type of contract time, it will be necessary to continue with Steps 4 and 5. Figure 2-13 presents the sub-steps in the procedure to complete Step 3. Sub-Step 2—Compare roughly between the PDE (with an anticipated letting date) and constraints. In some cases, a project has milestone and completion date constraints, but the contractor still has plenty of time to finish the project before the required completion date by letting the project early. If this is the case, the agency can select working days as the type of contract time instead of calendar days or fixed completion date. Sub-Step 3—Choose the contract time type based on other criteria. Without milestone and completion date constraints, the agency can still select a completion date as the contract time type based on other reasons (e.g., the impact on the traveling public and businesses and to avoid unwanted delays from contractors). Choose contract time type based on constraints Compare roughly between PDE and constraints Choose contract time type based on other criteria Sub-Step 1—Choose contract time type based on constraints. • If all project work must be completed by a specific date, choose fixed completion date. • If contract work is to be completed in a specific timeframe, choose calendar day. • working day. If project completion date is not critical, choose Figure 2-13. Step 3—Select contract time type (step and sub-steps). Step 3 Select Contract Time Type

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. The outcome of this step. The type or combined types of contract time (e.g., working days, calendar days, and/or fixed completion date). Note: If the type of contract time is working days, the result from Step 1 likely becomes the contract time. Otherwise, continue the procedure (Steps 4 and 5). The methods and tools used in this step. Can be done manually with a spreadsheet-based tool like Tool T2.5 (see Appendix A). Pros and cons. Emerging technology. See list provided in Table 2-2. Not applicable. Required documents and information. The estimated project duration in working days obtained from Step 1, milestones and completion date constraints obtained from Step 2, an anticipated letting date, and information about other relevant criteria affecting types of contract time (e.g., annual average daily traffic volume of the project). Figure 2-14. Overview of Step 3—Select contract time type.

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). Step 4 is used to develop a project-specic calendar to convert working days to calendar days. Based on the anticipated earliest letting time and the PDE in working days, contract time developers calculate calendar days for the project. Figure 2-15 presents the sub-steps that make up Step 4, and Figure 2-16 shows a visual example of dierent calendars. Sub-Step 1—Develop an integrated working calendar. Develop an integrated working calendar that incorporates various non-work constraints on contract time. An integrated calendar is a combination of two types of calendars: one applicable to all work activities and the other relevant only to some specific activities. Examples of those calendars are: • Base calendar—Specifies the typical weekly working schedule; • Holiday calendar—Typically includes state- recognized holidays; • Winter shutdown calendar—Includes the period of time that the project shuts down due to severe weather; • Environmental calendar—Includes the period of time that specific activities are not allowed to work due to ecological constraints; and • Landscaping calendar—Includes time restrictions for landscaping activities. Develop an integrated working calendar Sub-Step 2—Convert working days to calendar days. Convert working days to calendar days based on the developed, integrated working calendar. Convert to calendar days Figure 2-15. Step 4—Convert to calendar days (step and sub-steps). Step 4 Convert to Calendar Days

CTD Guide for DBB Projects 29   Figure 2-16. Integrated working calendars. Figure 2-16 shows an integrated working calendar that allows the contract time developer to convert project duration in working days into project duration in calendar days. Many non- working calendars may exist that can may aect a project; therefore, identifying and applying each non-working calendar, one by one, is important for a successful conversion. For example, even during the winter shutdown period, some non-weather-related activities may be performed with approval from the agency. In determining weather-related shutdown periods, many DOTs have established comple- tion date constraints in their specications. For example, the Iowa DOT recognizes that the arrival of cooler weather in the fall is not a simultaneous occurrence across the state (Iowa DOT 2017). For the establishment of contract periods, the agency has divided the state into three tiers (northern, center, and southern), and the completion date constraints dier for each tier. For projects that take place in the northern tier, Portland cement concrete (PCC) paving must be completed by mid-October and hot-mix asphalt (HMA) paving and resurfacing must be completed by the third week of October. For projects that take place in the southern tier, mid-November is the completion deadline for PCC paving and the rst week of November is the completion deadline for HMA paving and resurfacing. Some DOTs, such as the West Virginia DOT and the Virginia DOT, have established a xed duration for the winter shutdown period. e West Virginia DOT denes the 4 months from December through March as the winter shutdown period, and the Minnesota DOT has a 5-month winter shutdown period from November 15 to April 15. However an agency denes its winter shutdown period, it is advised not to apply the shutdown to all project activities because some project activities can actually be performed during the winter shutdown period. Step 4 Convert to Calendar Days

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) can be directly aected by environmental calendars. us, the contract time developer must have good knowledge of these specic cal- endars and properly incorporate them when creating the integrated working calendar. Similar calendars, such as landscaping calendars, can be found in the agency’s specications. Tool T2.5 uses the integrated working calendar concept and can greatly facilitate the con- version process by automating the entire calculation process. Tool T2.5 is further described in Appendix A and can be accessed in the downloadable CTD4HP Toolkit. Water Access Calendars (Massachusetts DOT) Calendar name Considers Allowable working window Water Access 1 Low flow periods June 1–September 30 (4 months) Water Access 2 Low flow periods AND fish migration July 15–September 15 (2 months) In-stream construction activities (Virginia DOT) In-stream activities Allowable working window • Pile driving • Cofferdams • Dredging • Excavation February 15–June 30 ** (4.5 months) Table 2-6. Example of an environmental calendar. Step 4 Convert to Calendar Days

CTD Guide for DBB Projects 31   Step 4 Convert to Calendar Days The outcome of this step. An integrated working calendar, including (a) days in which all activities are allowed to be performed, (b) days in which specific activities are not allowed to be performed, and (c) days in which no activities are allowed to be performed. Project duration in calendar days. Pros and cons. Not applicable. The methods and tools used in this step. Two possible ways to convert from working days to calendar days using the integrated calendar: • C1: Assign the calendar to the PDE schedule at the activity level if PDE is established using CPM. This approach considers the possible change of the critical path of the project schedule due to non-work constraints on some specific activities (i.e., days in which specific activities are not allowed to work). This task is supported by CPM software programs. With this method, the calendar can be created earlier in Step 1, and the conversion is automated and straightforward. • C2: Allocate the total number of working days into the calendar to find the number of calendar days or to add the total of non-work days to the number of working days. This approach can be applied when PDE is established using top- down methods (e.g., the estimated cost method) or when the start date, end date, and duration of each activity are not available. See Tool T2.5 (described in Appendix A). Emerging technology. Not applicable. Required documents and information. The anticipated letting time, the PDE in working days (obtained from Step 1), state regulations, federal or state agency guidelines, standards specifications, CTD manuals, construction manuals, project requirements, and design plans. Figure 2-17 provides an overview that summarizes Step 4. Figure 2-17. Overview of Step 4—Convert to calendar days.

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. Tool T2.5 also can be used to complete Step 5 (see Appendix A). Sub-Step 1—Determine PDE-based contract time (A). PDE-based contract time is calculated based on the PDE in working days (obtained from Step 1), the anticipated letting date, and the conversion of estimated project duration from working days to calendar days (completed in Step 4). Sub-Step 2—Determine constraint-based contract time (B). Constraint-based contract time is established based on milestone and completion date constraints (obtained in Step 2) and the anticipated letting date. Sub-Step 3—Determine contract time for letting. • If A is significantly smaller than B, the contract time should equal A. DOTs do not want to give contractors more time than needed because doing so might cause unnecessary disruptions to the traveling public and businesses. • If A is approximately equal to B, the contract time can be A or B. • If A is significantly higher than B, significant acceleration might be needed. Revisiting the PDE and constraints might be necessary to see whether some adjustments are possible. DOTs may apply incentive/disincentive provisions to accelerate construction time. The CTD procedure for DBB projects with incentive provisions is discussed in Chapter 3 of this guidebook. Determine PDE-based contract time (A) Determine constraint - based contract time (B) Determine contract time for letting Step 5 Determine Contract Time Figure 2-18. Step 5—Determine contract time (step and sub-steps).

CTD Guide for DBB Projects 33   Required documents and information. The project duration estimate in working days (obtained from Step 1), milestones and completion date constraints (obtained from Step 2), the anticipated letting date and type of contract time (obtained from Step 3), and the conversion from working days to calendar days (determined in Step 4). The outcome of this step. The PDE-based contract time (A) and the constraint-based contract time (B). The contract time for letting (if A is significantly smaller than or approximately equal to B) or the level of acceleration needed from the contractor (if A is significantly higher than B). Pros and cons. Not applicable. The methods and tools used in this step. Can be done manually using a spreadsheet-based tool like Tool T2.5 (see Appendix A). Emerging technology. Not applicable. Step 5 Determine Contract Time Figure 2-19. Overview of Step 5—Determine contract time.

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. e eects of those technologies are not limited to the con- struction phase but also apply to other phases of the project lifecycle (e.g., planning, design, and maintenance). at said, given the scope of this guidebook (i.e., construction contract time), this section focuses on the time impacts in the construction phase. Major advanced technologies that are actively used for highway projects include the following: • Global positioning system (GPS): – GPS is used for surveying tasks. – GPS also serves as the main component for other technologies (e.g., automated machine guidance) that have a direct impact on project duration. • 3D-engineered models: – ree-dimensional (3D) models are used in the design and construction phases. – 3D models help improve stakeholders’ spatial understanding of the project structures (e.g., multiple bridges at an interchange) and enhance communication among project partici- pants during construction. – 3D models can facilitate early detection of design conicts (e.g., clashes among utilities), thus avoiding rework and change orders during construction (Adam et al. 2015). – 3D models can be used as input for automated machine guidance to guide equipment operators. • 4D models: – 3D-engineered models are loaded with a construction schedule (e.g., CPM) to develop four-dimensional (4D) models. – 4D models can help improve the visualization of the construction process and trac phasing and detour through simulation. Such modeling also helps with the review of construction logic and the evaluation of design changes on the construction schedule (Adam et al. 2015). • Automated machine guidance (AMG): – AMG is primarily used to improve the productivity and quality of excavation, grading, and paving work (Adam et al. 2015, Jonasson et al. 2002). – A 3D AMG model needs to be uploaded in a computer that is mounted on a piece of equipment (e.g., excavators) to assist machine operators with grading and alignment by providing vertical and horizontal guidance in real-time (Adam et al. 2015, FHWA 2013). AMG equipment can automatically adjust its operations according to the uploaded 3D model (FHWA 2014). – AMG helps reduce construction project duration by increasing equipment productivity, reducing survey and staking time, and improving equipment logistics (FHWA 2013). • Intelligent compaction (IC): – IC is used for the compaction of road materials (e.g., soil, subbase, base, asphalt) to obtain more uniform compaction (Adam et al. 2015).

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. 2019). – IC can help increase productivity by minimizing the number of rolling passes while ensur- ing quality and reducing the time for checking the quality of compacted materials (Guo et al. 2018, Minchin et al. 2005). • Accelerated bridge construction (ABC) technologies: – “ABC uses safe and cost-effective planning, design, materials, and construction methods to reduce the onsite construction time involved in building new bridges or replacing and rehabilitating existing bridges” (FHWA n.d.). – Multiple ABC technologies help accelerate bridge construction. An example is slide-in bridge construction. “A new bridge is built on temporary supports parallel to an existing bridge. Once construction is complete, the road is closed, and the existing bridge structure is demolished or removed. The new bridge is positioned into place, tied into the approaches and paved within 72 hours” (FHWA n.d.). – ABC helps reduce “traffic impacts, onsite construction time, and weather-related time delays” (FHWA 2011). 2.4.2 Methods of Taking Account of Advanced Technologies in Establishing the PDE The technologies listed in the preceding section affect construction project duration at dif- ferent levels. Whereas some technologies such as AMG and IC directly affect the duration of particular work activities, others—such as 3D-engineered models—have an indirect influence on project duration. The next sections present four ways to deal with advanced technologies in establishing the PDE. Determine Percent Increases in the Production Rates of Affected Work Activities This approach can be used for AMG and IC, which affect some specific work activities. DOTs can conduct a case study to identify the percent increase for different scenarios (e.g., using various equipment and positioning methods or comparing production rates among historical projects using or not using advanced technology). A survey conducted by Vennapusa et al. (2015) showed that AMG has been used for different activities (e.g., fine-grading, trench excavation, and earth moving), with the productivity gain varying from 5 percent to more than 100 percent. Determine Percent Increases in the Total Project Duration Some technologies, such as 3D-engineered models and 4D models, may affect the entire project duration. It is challenging to identify a complete list of activities affected by the technology and determine the productivity gain of those activities. Instead, DOTs can identify two groups of completed projects with similar characteristics wherein one group has used the technology and the other has not. The average project duration for each group is then calculated and compared to determine the percentage increase when using the technology. The number of projects in each group should be large enough to ensure the reliability of the result. Include Advanced Technologies as Input Variables in Project Duration Estimation Models Some DOTs have developed automated tools to estimate the project duration based on the values of input variables (e.g., project characteristics and major quantities). The DOTs can modify

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. In this chapter, the section, “Development of Top-Down PDE Models,” provides more details. Identify Changes in Construction Logic When Using Advanced Technologies ABC technologies can accelerate construction project duration signicantly. e decision to use ABC usually is made in the planning phase, and ABC features and components are reected in project plans. At the end of the nal design phase, project duration estimators can take the technologies into account by reviewing project plans carefully and consulting with construction personnel (if necessary) to come up with an appropriate sequence of activities to reect the use of technology. 2.5 Development of Top-Down PDE Models Advanced scheduling methods, such as multiple linear regression, articial neural network (ANN), and case-based reasoning (CBR), can be used to quickly estimate the project duration without the requirement of detailed project information. e detailed description of each sched- uling method is provided in the description of Tool T2.1 in Appendix A. is rest of this section discusses a general procedure that DOTs can apply to develop a top-down PDE model using advanced methods. Figure 2-20 describes a generic procedure for developing a PDE model in which the following sub-steps are required: Identify Potential Input Variables Influential Factors Previous Prediction ModelsST EP 1 Collect Historical Data for Training Available Databases Quality & Quantity of DataST EP 2 Set an Evaluation Protocol Training Dataset Validation Dataset ST EP 3 Train the Model Optimum Architecture & Parameters Outsourcing ST EP 4 Validate & Apply the Model Expected Accuracy New Projects vs. Past ProjectsST EP 5 Procedures Influential Factors/Major Components/Options Figure 2-20. Generic procedure for developing a top-down PDE model.

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. Tool T2.4 (further described in Appendix A) provides detailed information about factors that inuence the PDE model. 2.5.2 Step 2—Collect Historical Data for Training Based on the identied potential input variables for the PDE model, DOTs need to nd some way to collect as much historical data as possible. e most eective approach is to examine available databases to gather relevant information for training the model. Additional data may need to be collected for various input variables. Considerations include the following: • e trade-o between the collection of additional data to increase model accuracy and the expenses of money and time by DOTs; • e quality and quantity of the gathered data determine the accuracy and reliability of the model; and • e importance of using consistent ways of recording and coding input variables (e.g., using latitude and longitude or districts to record project location). 2.5.3 Step 3—Set an Evaluation Protocol From the collected data, DOTs can set aside a hold-out validation dataset to validate the developed PDE model before using it. 2.5.4 Step 4—Train the Model Training a prediction model is challenging and time consuming. For example, the main chal- lenge of developing an ANN is that no xed rule or method exists to determine the optimum architecture or its parameter values for a specic problem (El-Gohary et al. 2017, Mustafa et al. 2013, Petroutsatou et al. 2012). erefore, an ANN designer oen needs to undergo a trial-and- error process of determining the appropriate architecture, constructing multiple models with dierent structures and parameters, and selecting an appropriate training algorithm for the problem under consideration before being able to select one that produces satisfactory results. A good strategy is for DOTs to outsource this step and use the hold-out dataset to evaluate the developed model. 2.5.5 Step 5—Validate and Apply the Model DOTs can use the hold-out dataset to evaluate the accuracy of the developed model. However, schedulers should be cautious about applying the model to a new project that is signicantly dierent from past projects (e.g., before applying a new construction technology) because the developed model is built upon past data. 2.6 References Adam, J., B. Cawley, K. Petros, D. Brautigam, R. Burns, S. Burns, J. Kliewer, J. Lobbestael, R. R. Park, and C. T. Jahren (2015). Advances in Civil Integrated Management. NCHRP Project 20-68A, Scan Team Report. Available at: http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP20-68A_13-02.pdf.

38 Systematic Approach for Determining Construction Contract Time: A Guidebook Chang, G. (2017). “Automation in Highway Construction: Success, Challenges, and Guidance.” Available at: https://docs.lib.purdue.edu/roadschool/2017/presentations/92/. El-Gohary, K. M., R. F. Aziz, and H. A. Abdel-Khalek (2017). “Engineering approach using ANN to improve and predict construction labor productivity under different influences.” Journal of Construction Engineering and Management, 143(8), 04017045. FHWA (2002). FHWA Guide for Construction Contract Time Determination Procedures. Federal Highway Admin- istration, Washington, D.C. Available at: https://www.fhwa.dot.gov/construction/contracts/t508015.cfm. FHWA (2011). Accelerated Bridge Construction Manual: Experience in Design, Fabrication and Erection of Pre- fabricated Bridge Elements and Systems. Federal Highway Administration, Washington, D.C. Available at: https://www.fhwa.dot.gov/bridge/abc/docs/abcmanual.pdf. FHWA (2013). “Executive Summary: Automated Machine Guidance with Use of 3D Models.” Federal Highway Administration, Washington, D.C. FHWA (2014). “The Use of Automated Machine Guidance on the Florida SR 417 Lane Widening Project.” Case Study (Spring 2014) Tech Brief. Federal Highway Administration, Washington, D.C. Available at: https:// www.fhwa.dot.gov/construction/3d/amg/pubs/hif13055.pdf. FHWA (n.d.). Accelerated Bridge Construction. Federal Highway Administration, Washington, D.C. Available at: https://www.fhwa.dot.gov/bridge/abc/. Guo, F., C. T. Jahren, J. Hao, and C. Zhang (2018). “Implementation of CIM-related technologies within trans- portation projects.” International Journal of Construction Management, 1–10. Idaho Transportation Department (2011). “Contract Time Determination in Project Development.” Idaho Transportation Department, Boise, ID. Illinois DOT (2017). “Chapter 66: Contract Processing,” The Bureau of Design and Environment (BDE) Manual. Illinois Department of Transportation, Springfield, IL. Available at: https://www.login-faq.com/idot- bde-manual-chapter-66/. Iowa DOT (2017). “Letting Guidelines – Section 11: Contract Periods/Innovative Contracting.” Office of Contracts, Iowa Department of Transportation, Ames, IA. Jonasson, S., P. S. Dunston, K. Ahmed, and J. Hamilton (2002). “Factors in productivity and unit cost for advanced machine guidance.” Journal of Construction Engineering and Management, 128(5), 367–374. Minchin, J., R. Edward, D. C. Swanson, and H. R. Thomas (2005). “Computer methods in intelligent compaction.” Computing in Civil Engineering (2005), 1–11. Missouri DOT (2004). “Contract Time Determination.” Missouri Department of Transportation, Jefferson City, MO. Mustafa, M. R., R. B. Rezaur, S. Saiedi, H. Rahardjo, and M. H. Isa (2013). “Evaluation of MLP-ANN training algorithms for modeling soil pore-water pressure responses to rainfall.” Journal of Hydrologic Engineering, 18(1), 50–57. Patel, D., R. Sturgill, G. Dadi, and T. Taylor (2019). “Evaluating the Performance of e-Construction Tools in Highway Resurfacing Projects.” In: Proceedings of the 36th International Symposium on Automation and Robotics in Construction (ISARC). IAARC Publications, 274. Petroutsatou, K., E. Georgopoulos, S. Lambropoulos, and J. P. Pantouvakis (2012). “Early cost estimating of road tunnel construction using neural networks.” Journal of Construction Engineering and Management, 138(6), 679–687. Vennapusa, P. K., D. J. White, and C. T. Jahren (2015). “Impacts of automated machine guidance on earthwork operations.” Proceedings of the 2015 Conference on Autonomous and Robotic Construction of Infrastructure (June 2–3, Ames, IA). Iowa State University, Ames, IA.

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Contract time affects the cost of construction, traffic disruption and public inconvenience, the economic impact of projects to the surrounding areas, and schedule risks.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 979: Systematic Approach for Determining Construction Contract Time: A Guidebook provides state departments of transportation guidance for producing consistently credible, reliable, and defensible contract time estimates.

Supplemental to the report is NCHRP Web-Only Document 298: Developing a Systematic Approach for Determining Construction Contract Time, a spreadsheet-based Toolkit, a Technical Memorandum, and a Presentation.

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