National Academies Press: OpenBook

Practices for Construction-Ready Digital Terrain Models (2021)

Chapter:Chapter 5 - Summary of Findings

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Page 39
Suggested Citation:"Chapter 5 - Summary of Findings." National Academies of Sciences, Engineering, and Medicine. 2021. Practices for Construction-Ready Digital Terrain Models. Washington, DC: The National Academies Press. doi: 10.17226/26085.
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Suggested Citation:"Chapter 5 - Summary of Findings." National Academies of Sciences, Engineering, and Medicine. 2021. Practices for Construction-Ready Digital Terrain Models. Washington, DC: The National Academies Press. doi: 10.17226/26085.
Page 41
Suggested Citation:"Chapter 5 - Summary of Findings." National Academies of Sciences, Engineering, and Medicine. 2021. Practices for Construction-Ready Digital Terrain Models. Washington, DC: The National Academies Press. doi: 10.17226/26085.
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Suggested Citation:"Chapter 5 - Summary of Findings." National Academies of Sciences, Engineering, and Medicine. 2021. Practices for Construction-Ready Digital Terrain Models. Washington, DC: The National Academies Press. doi: 10.17226/26085.

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39 Summary of Findings The primary objective of this synthesis study was to document current processes and strategies for the effective use and transfer of DTMs from design into the construction phase of highway projects. Secondary objectives were to identify DOTs that have experience using DTMs in construction and to provide an overview of implementation to date and lessons learned that identify success factors and challenges. Each objective was previously addressed in the survey results presented in Chapter 3 and the DOT case examples described in Chapter 4. The following sections revisit the primary findings of this NCHRP synthesis study. The information used to generate the conclusions is inclusive of the 40 DOTs that responded to the survey. When specific numbers are referenced, non- responding states are not included in the findings. 5.1 Extent of DTM Use in Construction and Inspection • Although 3D modeling and DTMs have been around for some time, their use is still inconsis- tent nationally: 15% of DOTs use DTMs on fewer than 10 projects annually, whereas 25% of DOTs use DTMs on more than 100 projects (Figure 9, N = 40). The results are further echoed in length of use: 11% of DOTs have less than 3 years of experience whereas 45% of DOTs have more than 10 years of experience (Figure 10, N = 40). • States have used DTMs most on corridor widening, intersection improvement, bridge construction or replacement, and road rehabilitation projects (Figure 18, N = 37). The larger the project budget, the more likely a DTM was used. In fact, only 5% of states have used a DTM on a project with a budget of less than $1 million. Over half (51%) of responding DOTs use DTMs on all projects regardless of project budget (Figure 17, N = 37). • A few states outsource their DTMs for all projects; a few others create them all in-house. For most states, in-house model creation ranges between 40% and 60% (Figure 11, N = 32). • Frequency of use in construction inspection varies also: 10% of DOTs never use DTMs in inspection, 24% rarely use them, 42% sometimes use them, and 24% often use DTMs when inspecting projects (Figure 14, N = 38). No survey respondent believed that his or her agency always uses a DTM during inspection. As noted in its case example in Chapter 4, PennDOT seeks to go fully digital through all phases of a project’s life cycle through its Digital Delivery 2025 initiative. • In the construction phase of projects, most DOTs use their DTMs for grade work (95%), quantity measurements (94%), survey verification (92%), field staking (89%), AMG (86%), and progress checks (86%). Essentially, agencies primarily use DTMs for geospatial field measurements. Fewer DOTs use the models for future activities such as work planning (49%) and cost analysis for maintenance (31%) (Figure 12, N = 38). In Chapter 4, ALDOT, MaineDOT, ODOT, PennDOT, and UDOT note that their contracting communities’ use of C H A P T E R 5

40 Practices for Construction-Ready Digital Terrain Models AMG pushed them forward to adopting and using DTMs in construction. That exposure and subsequent use stirred a vision for several agencies toward a future with reduced or no paper documentation on projects. 5.2 Policy Guidance for DTM Use • Although some states have significant experience with DTMs in both number of projects and length of use, little policy guidance is formally documented. The most frequently noted written specification language is that the DTM (or XML) is provided as “for information only” for contractors to use at their own risk (91%). Even for some advanced states outlined in the case examples, the final remaining hurdle to full digital project delivery is moving the model into the contract documents. There is a significant drop-off to the next most frequent policy language. The extent of DOT liability for the accuracy of the model (53%), standard surveying practices (47%), and extent of DOT liability for the use of the model in the field (44%) are the next most frequently documented policy statements. Less than a third (31%) of states describe file management protocols or model handover policy from design to construc- tion. (Figure 23, N = 36). • Contract document precedence remains in the typical order, with written specifications having priority over 2D plans and 3D models. Given that most states still do not include 3D models in contract documents, this finding is not surprising but could be changing in the near future. Although 38% of DOTs have not executed a project for which the DTM was part of the legal contract documents, they state that they plan to in the near future because the use of 3D models is increasing, and states are becoming more open to using 3D models as a legal contract document. Only 24% of states have executed a project with the 3D model included in the contract documents (N = 32). Additional information can be found in Appendix B. 5.3 Model Verification Processes • In the field, most states verify accuracy of the work built from the model by conducting independent verification of survey points (78%). Less than a third of states (31%) run actual model checks with the design model and the model used by the contractor. A few states conduct both field verification of survey points and model checks. One state mentioned that it compares point cloud data captured from either LiDAR or UAS photogrammetry to the contractor’s DTM (Figure 24, N = 32). In Chapter 4, MaineDOT notes the importance of similar location and number of survey points for model verification. If those vary signifi- cantly, it can lead to significant discrepancies between agency and contractor quantities. • If changes are made in the field, however, few states actually modify the DTM model once the contractor is using it. More than half of the states surveyed do not have the DTMs updated to an as-built condition; 25% of DOTs have their staff or consultant inspection staff keep the model updated as an as-built. A select few states have the designer or contractor make the as-built modifications of the DTM (Figure 25, N = 32). 5.4 Benefits and Strategies for Effective DTM Use in Construction • In the short term, DOTs believe that the most significant benefits that DTMs provide in construction are easier calculation of quantities, earlier identification of conflicts, reduced risk during bidding, and improved communication among project stakeholders. In general, states also believe that DTMs lead to fewer change orders and project delays (Figure 20, N = 37).

Summary of Findings 41 In the case examples, the DOTs noted the time savings and accuracies achieved for quantity measurement as meaningful benefits, along with the ability to support their contractors’ use of AMG. • DOTs were more strongly aligned with their vision of long-term benefits from DTM use. Those long-term benefits noted were cost savings, improved accuracy of plans, improved documentation of measurements, improved communication, better efficiency in construc- tion, and fewer claims and litigation (Figure 21, N = 38). Some noteworthy reductions in claims were mentioned in Chapter 4, particularly in the cases of MaineDOT, ODOT, and UDOT. • The successes discussed in the case examples seemed to be attributed to three main sources; supportive leadership, resource dedication, and collaborative contracting relationships. UDOT noted the importance of stable leadership that champions technology and educated risk-taking. Its administrative leadership has been relatively consistent for 20 years and is not afraid to fail with well-planned trials. From a resource standpoint, ODOT has dedicated staff comprising IT and end users to evaluate, test, implement, and support technology initiatives. There are proponents in MaineDOT for a similar group. PennDOT has an active survey- ing group that evaluates and supports emerging technologies. Finally, all DOTs reported positive relationships with their contracting partners and the importance of trust in those relationships. • Training is always an issue with any new or emerging technology in regard to how successful its implementation is. This area appears to have a wide range of strategies and approaches. Most states (84%) rely on informal peer training for their end users. Some also provide field-based (65%) or classroom-based (52%) training with hardware and software. Almost a third (32%) of states just provide reference material and rely on the end users to develop their own skills (Figure 15, N = 37). MaineDOT offers classroom style training but also one-on- one in the field training as needed. ODOT conducted training at every construction office in the state. It also requires an 8-hour training course before staff members can access surveying equipment. Regional training is offered on an as-needed basis or as updates occur. PennDOT has 2-day training requirements on technical and procedural issues. Several DOTs also mentioned benefits of these advanced skillsets not only in efficiency of work but also in attracting a future workforce. Working with 3D models, UASs, and GPS technology leads to a more sophisticated workforce and one that is positioned to attract younger generations. 5.5 Challenges and Knowledge Gaps • Even with numerous benefits and the examples of states with significant experience, many barriers remain to further use and implement DTMs. Training presents the most consistent roadblock for DOTs. Specifically, training for inspectors (70%), office staff (65%), and field survey staff (62%) are the most frequently mentioned barriers for further DTM use in con- struction. Other frequently noted issues are incomplete and inconsistent models (49%), designer lack of confidence in the model (41%), insufficient knowledge of equipment operators (38%), and cost of staying current with field technology (32%) (Figure 22, N = 37). • On the basis of the case examples, some more specific challenges emerged. DOTs have some uncertainty regarding newly available software. The transition to a new platform has a learning curve that should enhance workflows, but the DOTs interviewed are not there yet. In addition, some of the existing field software packages can struggle with complex models. Equipment costs can be an impediment and a difficult sell depending on budgets and decision makers in the DOT. Some states are also still struggling to overcome certain regulatory and legal issues such as accepting electronic stamps and electronic signatures, and defining the makeup of a plan set of record.

42 Practices for Construction-Ready Digital Terrain Models The findings from this synthesis project demonstrate some inconsistencies in the use of DTMs in construction. DOTs have a wide range of experience in both the number of projects and the years of experience with DTMs. The case examples suggest that the states with inno- vative, risk-seeking cultures related to technology adoption and collaborative relationships with their contracting communities seemed to be the most advanced in their use of DTMs in construction. Often, the contracting community pulled those states forward: contractors’ adoption of AMG forced their partner states to investigate the models driving the equipment. In addition, states with higher use of alternative contracting methods such as DB and CM/GC found it easier to share the design model in the construction phase because of early contractor involvement. Training and skillsets are barriers to further use of DTMs in construction. Some DOTs lack well-developed training programs for their end users, while others lack the in-house surveying knowledge to effectively leverage the models in construction. Ultimately, the next major advancement in DTM use in construction for the DOTs surveyed and interviewed is to incorporate the models into contract documents. A select few states have successfully integrated models into contract documents. Most have not but do have near-term aspirations to do so, whereas others still have no interest in including the model in the contract. For those DOTs working toward that integration, adopting necessary policy changes, training needs, and hardware and software costs (both initial and maintenance costs) seem to be the current focus. Finally, as noted in the MaineDOT case example, if contractors are going to build DOT projects digitally, then inspection tasks can also be done digitally.

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Digital terrain models (DTMs) are three-dimensional (3D) models of the ground surface showing natural features such as ridges and breaklines.

The TRB National Cooperative Highway Research Program's NCHRP Synthesis 560: Practices for Construction-Ready Digital Terrain Models documents processes and strategies used by state departments of transportation (DOTs) for the use and transfer of DTMs from design into the construction phase of highway projects.

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