Driving collaborative success across phases in public projects: the role of boundary spanning in fostering synergetic momentum Open Access

In the development of public infrastructure, collaborative projects have become crucial for providing better project service delivery, for instance by procuring external expertise (Hodge and Greve, 2007), and by managing the risk allocation among stakeholders (Chen and Manley, 2014). Existing research shows that during collaborative processes, there are instances when success factors are undermined, leading to disruptions in collaboration (Verweij, 2015a; Busscher et al., 2022), for example, due to imbalances in risk allocation (Tallaki and Bracci, 2021). Factors such as conflicting priorities and lack of alignment can contribute to the breakdown of synergy within collaboration (Stadtler and Karakulak, 2020). Such discord can hinder progress, diminish motivation and impede the achievement of common objectives (Busscher et al., 2022). Addressing collaboration challenges requires prompt action to rebuild trust, reinvigorate collaborative spirit and maintain synergetic momentum (SM) (Thomson and Perry, 2006). Wu et al. (2017) showed that strengthening formal communication between partnering organizations enhances project success by enabling teams to manage tasks, process and relationship conflicts more effectively. This suggests that maintaining SM towards project success necessitates deliberate investment in fostering collaboration.

Public infrastructure project outcomes are impacted by project management activities (Nallathiga et al., 2017; Satheesh et al., 2023) and among the various phases in the project lifecycle, the planning and implementation phases have the highest levels of stakeholder participation (Heravi et al., 2015). Given the importance of managing social interactions within the collaboration process, boundary spanners may play a role in managing stakeholder interests and motivations (Huxham and Vangen, 2000; Levina and Vaast, 2005; Williams, 2002). Boundary spanners are described by Van Meerkerk and Edelenbos (2018a) as “people who proactively scan the organizational environment, employ activities to cross organizational or institutional boundaries, generate and mediate the information flow, coordinate between their ‘me’ organization or organizational unit and its environment, and connect processes and actors across these boundaries” (p. 58). In public infrastructure projects, project managers or other project team members can engage in boundary-spanning activities (BSAs) to support relationships, as well as maintain communication across boundaries.

Although research has recognized the importance of boundary spanning for fostering collaboration in public infrastructure projects (Satheesh et al., 2023), most studies still conceptualize boundary spanning in static or cross-sectional terms, capturing it at a single point in the project lifecycle. Moreover, although prior work has studied boundary spanning in relation to types of boundaries (Tushman and Scanlan, 1981; Levina and Vaast, 2005) innovation (Acharya et al., 2022) governance networks (Van Meerkerk and Edelenbos, 2018b), and functions of boundary spanners (Williams, 2002), these strands offer limited insight into how boundary spanning unfolds during transitions between project phases. While boundary spanners are expected to facilitate transitions across project phases (Whyte and Nussbaum, 2020) by handling significant events across project phases to maintain SM among stakeholders (Moradi and Kähkönen, 2022). There is a gap in understanding how boundary spanners strategically move between phases within the same project to sustain collaborative momentum. To address this gap, this study examines how BSAs contribute towards critical success factors (CSFs) that indicate collaborative success and how this helps to sustain SM across project phases. This approach highlights how engaging in BSAs can reshape collaboration in a given management context and influence what becomes possible in subsequent phases by conceptualizing collaboration as a dynamic, event-driven process. The research question addressed in this study is: How do BSAs enhance CSFs to maintain SM with stakeholders across different project phases in the face of significant events? By examining the dynamic role of boundary spanners in navigating significant events and sustaining SM over extended periods, this research provides empirical evidence of how boundary spanning contributes to long-term collaboration and project success.

We adopted a case study approach to examine the specifics of a series of events, capturing the nuances and complexities that are often overlooked in larger quantitative studies (Flyvbjerg, 2006). The “A24 Blankenburgverbinding” project in the Netherlands is a relevant project for examining SM, as it achieved collaborative success and prioritized integrated spatial quality (Leendertse et al., 2016; van Putten and van Os, 2022; Baccelli, 2020). This is one of the largest public–private partnership (PPP) projects in the Netherlands, costing over two billion euros (Provinciale Zeeuwse Courant, 2024). This case was selected based on public information showing it as a successful public-private collaboration project (Nedam, 2024) and corroborated by a database developed by the authors containing 58 projects implemented by Rijkswaterstaat (the executive agency of the Dutch Ministry of Infrastructure and Water Management) (Satheesh et al., 2023). This database was developed from survey data, which showed that the “A24 Blankenburgverbinding” project has high levels of boundary spanning as well as good collaborative outcomes in the project team's interaction with most of the stakeholders. The data for this study were collected through document analysis and interviews with the managers from the integrated project management (IPM) team, from both the public and private partners in the PPP, who are responsible for the execution of the project as well as communicate with the top management and with stakeholders from municipalities.

SM is defined by Hodge and Greve (2007) as the collaborative energy and combined efforts generated when multiple partners work together towards a common goal, leading to greater effectiveness than they would achieve acting alone. SM plays a crucial role in maintaining coherence and effectiveness across distinct project phases, especially when multiple parties must align their goals and resources (Birkinshaw et al., 2017). The characteristics of the planning and implementation phases differ, as the former focuses on openness to ideas and flexibility in agenda-setting (Baartmans et al., 2025) and the latter focuses on achieving efficiency in project outcomes (Verweij, 2015b). This calls for a re-orientation of the management approaches across the two phases (Morse and Stephens, 2018). In the planning phase, the project team engage in BSA to gather project support (Larsen et al., 2018). Still, from previous projects, we can observe that there is a tendency to limit stakeholder engagement so as not to derail the project plans (Morse and Stephens, 2018). BSAs, however, are just as crucial in the implementation phase because they enable handling unforeseen changes (Verweij, 2015a). The project management team needs to proactively solve issues which arise during the implementation of a project, to facilitate SM (Conteh, 2013).

Approaching collaboration with keen interest and openness to different perspectives can help sustain SM through boundary-spanning efforts (Jones and Noble, 2008), which is particularly important as projects often encounter anticipated or unforeseen events that can influence CSFs (Lehtinen and Aaltonen, 2020). Events are defined as significant incidents that substantially influence the project's trajectory, often requiring early identification to mitigate their impact (Grau et al., 2016). Examining events across different project phases in more detail helps explore the depth, intensity and duration of stakeholder interactions within a collaboration, providing insights into the degree of collaboration (Larsson and Larsson, 2020). While events could shape project outcomes, to a large extent, their unpredictable nature can also pose challenges, making it essential for project managers to develop robust strategies for identification and response (Sunny et al., 2024), so as to maintain SM. Figure 1 is a diagrammatic representation of the interrelation among SM, project phases, CSFs and BSAs.

CSFs play a critical role in maintaining SM throughout the planning and implementation phases, not as stable preconditions, but as dynamic factors that require ongoing reinforcement. The identification and management of these factors is essential for ensuring that projects not only meet their objectives but also adapt to the complexities inherent in the infrastructure sector (Heravi et al., 2015). Jacobson and Choi (2008) demonstrated that high levels of shared vision, commitment and paired factors such as open communication and trust with collaboration are central to effective project delivery. Maintaining SM throughout the collaborative process often requires the project team to be dynamic and adaptable to changing circumstances (Stjerne et al., 2019).

From a governance perspective, CSFs can be instrumental in understanding the impact of boundary spanning on project development. The governance dimensions that contribute to maintaining SM are coordination and definition of roles in decision-making (Kujala et al., 2021). Table 1 shows how CSFs contribute to maintaining SM. The CSFs included in this study were selected because they are central to collaborative projects and suitable for assessing the influence of boundary-spanning activities. These factors form a structural relationship: foundational relational elements (mutual trust, common goal and shared vision) create the conditions enabling operational mechanisms (open communication, commitment to win-win philosophy), which are activated through leadership practices (leadership and conflict resolution, top management support). Together, they capture the relational quality of a collaboration.

1. Mutual Trust: Mutual trust fosters collaboration, enhances communication and facilitates the sharing of information, which are essential for the successful execution of complex projects (Tokede et al., 2022). Trust is a predictor of project performance and stakeholder satisfaction within project teams (Jacobson and Choi, 2008).

2. Common goals and shared vision: When all parties involved in an infrastructure project align their goals, this creates a unified direction, enhancing project coherence. This alignment is crucial as it facilitates the integration of diverse perspectives and expertise, which can lead to more innovative solutions and efficient problem-solving during both planning and implementation phases (Hoeft et al., 2021).

3. Open communication: Effective communication facilitates the alignment of goals and expectations among stakeholders, which is crucial during the early stages of project planning (Setiawan et al., 2021).

4. Commitment to win-win philosophy: Developing win-win strategies can lead to innovative solutions that address the diverse needs of stakeholders (Bryson et al., 2015). The win-win philosophy acts as a compass, motivating stakeholders to look for solutions that benefit all parties.

5. Leadership and conflict resolution. Leaders can follow a behaviour that promotes a culture of open communication, thereby enabling team members to express their thoughts openly (Sørensen et al., 2021).

6. Top management support: The influence of top management support spans various dimensions, including resource allocation, strategic alignment and stakeholder engagement, all of which are essential for maintaining SM throughout the project lifecycle (Stjerne et al., 2019).

Boundary spanning by project team members complements formal contractual agreements by navigating bureaucratic barriers and attempting to informally resolve issues. In this study, any team member can initiate and participate in BSAs to manage their organizational environment and establish external linkages (Ancona and Caldwell, 1992). A relational style of management develops mutual trust and respect through boundary spanning and this can maintain SM among partners (Noble and Jones, 2006). Vosman et al. (2024) observed that different types of boundary spanning take priority at different points of the project and for different circumstances. We focus on the activities of boundary spanners in significant events during the project lifecycle.

Relational activities (RA). Boundary spanners build coalitions, forge relationships, gather support to solve issues and strategically use social capital (Williams, 2011). They engage in active communication and coordination with stakeholders, which enhances the quality of collaboration and project performance (Satheesh et al., 2023). This activity can contribute in particular to the CSFs of building mutual trust and to developing common goals and a shared vision.

Mediation and facilitation activities (MF). Boundary spanners give due consideration to the concerns and needs of both the home and partnering organizations. They establish a safe space for dialogue where partners can freely express their concerns through active listening and reframing to help partners understand each other's perspectives (Williams, 2002). When partnering, MF helps to explore commonalities that become the frame of reference for future interactions and contribute to CSFs of open communication and commitment to win-win philosophy (Moradi and Kähkönen, 2022)

Information exchange and knowledge sharing activities (IK). Boundary spanning in projects can help to process new information by having a predictable knowledge flow in projects. Boundary spanners support knowledge exchange and the establishment of communities of practice, which are vital for overcoming silos (Roberts and Beamish, 2017). IK supports CSF leadership and conflict resolution by fostering mutual understanding, minimizing information asymmetry and ultimately reducing unnecessary expenditures (Wu et al., 2017).

Coordination and negotiation activities (CN). In an inter-organizational collaboration, boundary work entails establishing a project workflow, creating room for the adaptation of new practices, enabling a stable project environment and managing inter-organizational relationships (Vosman et al., 2024). Boundary spanners connect with different people by bridging organizational boundaries and building a network (Jones and Noble, 2008). They can mediate conflicts by influencing the network to balance competing interests by finding common ground, and this fosters trust (Williams, 2002). Projects often involve tensions that hinder coordination, requiring negotiation across phases and boundary spanning facilitates proactive conflict management, enhancing CSF trust among stakeholders (Stjerne et al., 2019).

In this study, we conceptualize collaborative success to be dependent on maintaining SM throughout the project lifecycle. SM, in turn is influenced by CSFs that are dependent on BSA taking place during significant events (see also Figure 1).

Our research strategy revolved around the analysis of BSA observed in the events occurring during the planning and implementation phases of a complex public infrastructure project. We chose a single case study design as this is suitable for analysing why certain decisions are taken at a particular event in a project, because the decisions are often very contextual (Engwall, 2003). We selected the “A24 Blankenburgverbinding” project with a design-build-finance-maintain (DBFM) integrated contract, which was initiated by Rijkswaterstaat, the executive agency of the Ministry of Infrastructure and Water Management in the Netherlands. The project involves constructing a 2x3-lane highway, two new junctions at intersections, and two tunnels (one across the river Scheur and a land tunnel) to link the A15 and A20-highways – see Supplementary Material 2. The land tunnel (called Holland Tunnel) spans a length of 500 meters, and the underwater tunnel (called Maasdelta Tunnel) measures 900 meters. The goal of the project is to improve accessibility and mobility through sustainable infrastructure in the Rotterdam region.

The data for this study were collected through multiple sources, namely, interviews, secondary documents and newspaper articles. This triangulation of sources enhanced the consistency and credibility of the results, providing a deeper insight into the case's specificities. We adopted an iterative qualitative approach, initially analysing project documents (Supplementary Material 1) to gain a preliminary understanding of contract arrangements with public and private stakeholders. This was followed by semi-structured interviews using purposive sampling to gather managers' first-hand project experiences. All interviews were conducted face-to-face, between September and December 2023, lasting 45–90 min. A total of nine interviews (I1 to I9) were conducted with senior-level managers involved in the project, including directors, managers, project team members and municipality officials (Supplementary Material 3).

A range of interview questions were asked regarding interviewees' role and responsibilities in the project (see Interview Guide in Supplementary Material 4). The interviews revolved around respondents' involvement in the project, in the collaborative process and the BSA engaged in, both within and external to the project. Depending on the interviewees' preference, interviews were conducted in either Dutch or English, with one of the two interviewers being a native Dutch speaker.

The interview material was analysed through three iterative coding cycles in Atlas.ti 24. First, we conducted open coding to identify activities, interactions, and developments mentioned by respondents, resulting in 117 initial codes across 268 quotations. Second, we clustered these codes around events mentioned in the interviews and merged or removed redundant or overlapping codes. In this step, we focused on events that put pressure on collaboration among stakeholders, as these moments made it possible to examine which BSAs were used and how these influenced CSF and SM. The research findings validate this by showing that the collaboration was strengthened through BSAs as it can be seen through the presence of SM and CSFs. Third, we mapped the refined codes onto the analytical framework, distinguishing four BSAs, six CSFs and manifestations of SM derived from the literature on public–private collaboration.

The final coding structure consisted of seven collaboration-related events, four BSA categories, six CSFs and SM. In the final coded dataset, the four BSA categories were linked to 28 quotations, the six CSFs to 18 quotations, SM to 26 quotations and the seven events to 33 quotations in the interviews. The coded segments formed the basis for the analysis presented in the results section.

To further expand our understanding of the seven events identified in the interviews, we searched LexisNexis for newspaper articles mentioning the keyword “Blankenburgverbinding”. This resulted in the identification of 1,303 newspaper articles concerning the Blankenburgverbinding project (as of 24th September 2024). We first excluded duplicate articles reporting the same incident across different media outlets, which reduced the dataset to 75 articles. A further content review identified 24 relevant articles corresponding to the events depicted in Supplementary Material 2 along the project lifecycle (see Supplementary Material 5). These newspaper articles were subsequently coded in ATLAS.ti using the same coding scheme as the interview data.

Overall, data analysis followed a hybrid approach that combined inductive pattern identification with deductive coding based on the theoretical framework. This approach made it possible to identify the BSAs that were enacted across the project lifecycle and that contributed to the collaborative success through CSFs and through maintaining SM in the project.

Our study focused on examining how BSAs influence CSFs contributing to maintaining SM in a project by mapping them through events. The observed events are distributed throughout these phases – three events in the planning phase, and four events in the implementation phase. The description of the events across the project lifecycle is depicted in Supplementary Material 6 and Table 2 shows the key events (mentioned in the interviews) that majorly impacted the project trajectory (when looking at it in retrospect) by engaging in BSA, which contributed to the CSFs.

In Table 2, the response to Event 1 portrayed a boundary-spanning approach that was “We want to learn from your point of view, and your knowledge of the area to make the project better. That's how the design of the highway is made incorporating the wishes and ideas of the different participants” (Interviewee 3). Through RA, MF and IK, the protests by environmental groups and the municipality against the construction of the tunnel gradually shifted into a discussion of aspirations with various stakeholder groups for broader enhancements to the area surrounding the infrastructure (Interviewee 6). It can be observed that in Event 1, intensive stakeholder workshops brought residents, municipalities, non-governmental organizations (NGOs) and technical experts into structured dialogue, allowing concerns about the tunnel to be translated into concrete design wishes. The BSAs of relational, mediating and information-sharing activities strengthened mutual trust, open communication and leadership in conflict resolution as CSFs, which in turn acted as antecedents that enabled SM by turning protests into co-creation and sustaining collaborative engagement around a jointly improved design.

In comparison, the MF activities in Event 2 helped to gain resources and support for the project. The ministry supported the initiative by approving a seed amount of 25 million euros for executing an Area Quality Program consisting of 30 sub-projects (Interviewee 1). The IPM team facilitated a discussion between residents of neighbouring municipalities to figure out the priority order of the projects. Interviewee 3 said that “Owing to these discussions, the surrounding municipalities also wanted to invest so that all projects could be realized and that's now the current Area Quality Program”. This helped maintain SM by building a shared investment agenda and long-term regional cooperation.

In Event 3, the boundary spanning was focused on engaging in CN activities to mitigate delays and disruptions in project execution. This meant securing top management support was essential for the successful implementation of the strategy. SM was maintained by anticipating nitrogen risks and preparing solutions early, preventing disruptive legal delays. Similarly, in Event 4, CN activities helped in minimizing disturbance to the schedule by discussing the contractual responsibilities later. This demonstrated that maintaining a common goal and shared vision facilitates efficient issue resolution. This helped in maintaining SM by replacing blame with joint problem-solving.

Event 5 exemplifies how unforeseen disruptions, such as COVID-19, can impact even well-planned projects, requiring innovative problem-solving. In this case, parallel work at two locations significantly supported the project schedule. The IPM team and private partners successfully persuaded top management to make substantial, albeit risky, amendments to their agreements. This helped maintain SM through “best-for-project” collaboration, enabling schedule gains and strengthening inter-organizational alignment. The director of Damen Verolme, Peter Altena noted that constructing the tunnel elements in the dry dock showcased capabilities beyond maritime activities, representing a win-win outcome (Co-construction, 2022).

During Event 6, the IPM team, through boundary spanning of RA and MF, was able to leverage strong relations built through stakeholder workshops and discuss the issue with the local community to develop a plan, which resulted in conducting campaigns to promote local businesses and this helped maintain SM. In Event 7, developing mutual trust through RA and CN fostered collaboration between public and private partners, promoting accountability over blame (Interviewee 2), thus protecting the partnership that underpinned ongoing SM.

BSAs are present in combinations across the events. Based on Table 2, Figure 2 illustrates which activities and CSFs were associated with each event.

Analysing the CSFs based on their prominence in different project phases reveals distinct patterns. From Figure 2, it is apparent that open communication was predominant in the planning phase (observed in two events) and commitment to win-win philosophy was found mainly in implementation phase. In their study, Moradi and Kähkönen (2022) categorized open communication as an operational factor necessary for fostering productive collaboration between partners, while they classified commitment to a win-win philosophy as an organizational success factor essential for managing effective governance within a project. The difference in categorization shows that there was an evolving stakeholder dynamic, with early stages focused on relationship building (with the help of RA) and later stages on project execution. In event 2, through MF, the IPM team could effectively assess trade-offs and establish clear priorities by openly communicating. Although MF and RA were common in events 1 and 5, their roles shifted across phases, initially fostering stakeholder engagement amid opposition and later minimizing disruptions by leveraging relationships and securing top management approval for contract modifications. This resonates with the findings from previous studies, where each phase had distinct stakeholder dynamics, sustaining relationships established in the planning phase being essential for adapting to unforeseen circumstances in the implementation phase (Dewulf and Garvin, 2020). It becomes evident from these examples that MF emphasizes maintaining collaboration even in challenging circumstances, ensuring that difficulties do not lead to disengagement from the project. Instead of withdrawing from cooperation, the preferred approach was to engage in open dialogue and constructive discussion to address issues and find mutually beneficial solutions (Interviewee 3).

Mutual trust remained consistently present in one event each in both the planning and implementation phases. In the planning phase, mutual trust contributed to fostering a project culture that facilitated collaborative engagement. The IPM team was transparent (IK) about the extent of stakeholders' influence on decision-making, and this approach was essential for managing expectations and fostering trust among stakeholders (Interviewee 1). From the results, we know that involving stakeholders early on through workshops, while there was still adaptive room to make changes to the infrastructure development plan, helped build trust. Interviewee 6 corroborated this by taking the example of CSF of mutual trust, saying that “the trust you built in your planning phase should be a basis for the implementation phase”. Literature suggests that informal discussions during planning facilitate smoother project execution over time (Dewulf and Garvin, 2020). Facilitating mutual trust was a result of IK, which showed to enhance trust when executed during the planning phase of a project (Wu et al., 2017). Mutual trust persisted throughout event 7 and studies have shown that it takes constant effort to maintain trust in a persistently changing project environment (Dewulf and Garvin, 2020). Unforeseen blockages to immersion of the tunnel element resulted in delays and needed the team to work together to solve it by engaging in RA and CN.

Leadership and conflict resolution were present in both phases, with a more pronounced presence in implementation. During the planning phase, the focus was on fostering an environment through boundary spanning in which team members felt comfortable approaching the team lead with challenges (through RA), facilitated by an approachable leadership style. In the implementation phase, the emphasis shifted towards eliminating distinctions between the IPM team and the contractor's team in problem-solving efforts. Even when an issue arose that was within the contractor's scope, the IPM team lead adopted a reflective approach, questioning why the issue was not anticipated (Interviewee 1).

Further, Figure 2 underscores that top management support was of greater significance in the planning phase as compared to implementation, whereas the reverse held for common goal and shared vision. In the planning phase, support from top management was critical for initiating the discussion of prioritizing and resource management (Stjerne et al., 2019) through boundary-spanning MF (event 2) and preventing further delays through pre-verdict contracting by CN (event 3). In the implementation phase, the IPM team had top management support for working in parallel on-site and at the docks through RA and MF (event 5) and this demonstrated that outward orientation can help in gathering resources and support for the project (Verweij et al., 2017).

Fostering common goal and shared vision among stakeholders by adapting plans based on stakeholder inputs (event 1) provided a solid foundation for the implementation phase, enabling stakeholders to transcend individual interests and prioritize collective problem-solving. Similar to the planning phase, the IPM team adhered to an approach of transparency by actively engaging in relational activities, as well as CN in the implementation phase. In events 4 and 6, the IPM team acknowledged their inability to meet the established agreements, demonstrating transparency and accountability. By communicating changes to the plans, they ensured that all stakeholders had adequate time to adjust and accommodate the necessary modifications (Interviewee 7). Generally, it could be observed that the public and private partners had a “best-for-project” mentality during the implementation phase (events 4, 6, 7), where the partnering organization did not spend time on discussing whose responsibility it was but rather sought to find solutions through CN (Kujala et al., 2021). By investing in relational and facilitation activities during the planning phase, partners built the trust that later enabled a shared vision, a common goal and a deliberate search for win–win outcomes in the implementation phase.

Three main findings emerge from our analysis. Together, these three findings are able to advance the understanding of how boundary spanning contributes to CSFs that help in maintaining SM from a public management perspective. First, we find that CSFs need to be considered as dynamic factors, requiring ongoing enhancement through BSAs across events. While existing public management literature identifies CSFs in collaborative projects (Jacobson and Choi, 2008), and collaboration theory tends to treat CSFs such as trust, shared vision and open communication as stable conditions that persist once established, our findings show that CSFs must be actively re-established in response to significant events. For example, the mutual trust built during the stakeholder workshops of Event 1 did not automatically carry over to the soil contamination crisis of Event 4, where a shared vision had to be reconstructed through renewed negotiation. This suggests that CSFs are better understood as event-contingent outcomes of boundary spanning rather than durable project assets. Our study therefore advances theory by demonstrating that BSAs function as dynamic mechanisms that continuously reinforce CSFs across project phases, shifting the theoretical lens from identifying what matters to understanding how collaborative effectiveness is maintained over time.

Second, we find that in complex PPPs, SM arises when multiple CSFs are activated through multi-level boundary spanning, enabling partners to turn challenges into improved collaborative performance. Building on Hodge and Greve's (2007) conceptualization, we provide an empirical operationalization of SM by demonstrating how it manifests through shared commitment, joint responsibility, collective action and improved collaborative efficacy during events. Our findings show that SM represents the collaborative energy generated when partners actively work together through challenges, transforming resistance into co-creation (Event 1), blame into joint problem-solving (Event 4) and crises into shared challenges (Event 7). Importantly, our analysis shows that SM manifested only when multiple CSFs were simultaneously present and reinforced by specific BSAs. Maintaining this momentum required boundary spanners to operate both simultaneously and sequentially across stakeholder groups, for example, building interpersonal trust with stakeholders during workshops (Event 1) while securing top-management commitment at the organizational level (Events 2 and 3). This oscillation was not incidental but strategically necessary, suggesting that effective boundary spanning in complex PPPs is inherently a multi-level practice. Together, these findings enrich public management theory by establishing SM as an outcome variable that emerges from the configurational alignment of CSFs and multi-level BSAs.

Third, we find that the activities of boundary spanners are phase-based, contingent on structural and relational conditions, and help to align competing interests through CSFs and to sustain SM. The boundary-spanning literature typically conceptualizes boundary spanning as the bridging of diverse organizational boundaries to enable collaboration and knowledge sharing (Collien, 2021; Cao et al., 2021), and broadly argues for its general value across collaborative settings (Williams, 2013). By demonstrating that any team member can initiate and participate in BSAs, we contribute to theory by framing boundary spanning as a distributed organizational capability rather than a specialized function. Our findings empirically reinforce the relevance of relational activities, mediation and facilitation, coordination and negotiation, and information exchange in public infrastructure projects, showing that these activities collectively support relational management and the pursuit of collaborative advantage.

We refine this view, however, in two important ways. First, building on Bartel-Radic and Munch (2023), we conceptualize boundary-spanning capacity as a phased, event-activated resource rather than a uniformly deployed practice. CSFs such as mutual trust, open communication, leadership in conflict resolution and shared vision function as both relational dynamics and structural enablers of project success: through successive acts of engagement, boundary spanners reinforce trust and shared goal orientation, thereby aligning competing interests into cohesive action and sustaining SM (Hardy et al., 2003). Second, our evidence nuances the dominant assumption that more interaction and communication necessarily lead to better collaborative outcomes. In several events, the project management team deliberately narrowed its BSAs, suspending broader stakeholder engagement (e.g. Event 3) to enable focused technical and legal action. This selective restraint preserved forward momentum, suggesting that boundary-spanning effectiveness lies not only in what activities are deployed, but in the deliberate sequencing and omission of others.

Furthermore, our analysis shows that the same BSA can activate different CSFs depending on the phase and type of event. Mediation and facilitation, for instance, strengthened open communication and mutual trust during the planning phase (Events 1 and 2), but were deployed during the implementation phase to reconstruct a shared vision under budget and technical pressure (Event 4). This indicates that the BSA–CSF relationship is phase-related rather than generalizable.

With the help of the results generated in this study, public managers can match specific BSAs to specific collaborative challenges. The case study shows that effective boundary spanning involves not just discrete activities but sustained relational engagement over extended periods, supporting theoretical frameworks emphasizing relational continuity for long-term project success. Ensuring dynamic continuity of boundary spanning through planning and implementation phases, reinforcing arguments that sustained relational engagement and institutional memory are essential for long-term project success (Stjerne et al., 2019).

The study highlights the importance of structured workshops and clear participation rules in maintaining stakeholder engagement, even under conflict or crisis. Stakeholder diversity, consisting of governmental, non-profit, community and specialist actors, requires inclusive approaches that flexibly integrate feedback to build trust, a practice relevant for project managers in similar development projects. Transparent, early and ongoing communication emerged as critical for confidence building among stakeholders. The project team's approach to maintaining dialogues even during smooth operations or crises proved instrumental in trust retention. This early stakeholder engagement initiative can be found in other contexts as well, such as the European Commission's Pact for Engagement framework, which emphasizes early, regular and meaningful stakeholder engagement through designated engagement champions and facilitation structures (European Commission, 2023).

Our analysis confirms that proactive leadership and conflict resolution skills can transform opposition to projects and arising disputes into constructive collaboration opportunities. Facilitators who mediate firmly yet empathetically serve as enablers in overcoming challenges. The study is practically relevant to stakeholders engaged in generating public value by indicating that BSAs need to be tailored to different project phases, invest in relationship-building and information-sharing activities in early project phases and prioritizing collaboration beyond short-term issues by stabilizing momentum over the whole project life.

We conducted an in-depth examination of seven key events that occurred during the planning and implementation phases of the A24 Blankenburgverbinding project. Our aim was to investigate the role of BSAs in facilitating CSFs to sustain SM, thereby contributing to the overall collaborative success of the project. The findings underscore the central role of boundary spanners in continuously working on stakeholder relationships across phases in a project lifecycle, which proved crucial for maintaining collaboration over time (Moradi and Kähkönen, 2022). While this study provides detailed insights into how BSA and CSFs interact during significant events, the specific contributions of the different stakeholders within the network could be explored further. Future research could therefore explore the role of different stakeholders in undertaking BSAs. This provides practitioners with an actionable repertoire of boundary-spanning tools tailored to different project phases and challenges. Overall, this study contributes to an advanced understanding of the different BSAs across the various project phases and how they influence CSFs. It also highlights the importance of recognizing and supporting the work of boundary-spanning individuals, whose sustained efforts are essential for (re)conceptualizing and achieving effective collaboration in public infrastructure projects.

This research was conducted as part of the long-term research co-operation between Rijkswaterstaat and the University of Groningen. The authors would like to thank all the interviewees for their participation in this study.

The supplementary material for this article can be found online.