Faith, form, and the bin: the CT-VR framework for culturally tuned recycling infrastructure in Gulf cities

1 Introduction

Doha serves as a prime example of “petro-urbanism,” with its development and transportation systems funded through petroleum resources. In less than two decades, the population of the capital expanded from a pearl-diving port to a metropolitan region with over 1.2 million people, achieved via large-scale mega-projects rather than gradual or incremental development (Shandas et al., 2017). These developments impact the quantity of solid waste generated, with Qatar generating over 2.5 million tons of municipal solid waste (MSW) annually. Of the total, 60% is organic, and the other 40% is deemed recyclable (Talballa and Gichuru, 2023). According to Bello (2018), solid waste encompasses only non-liquid discarded materials deemed undesirable or of no value, produced by households, commercial, and industrial endeavors within a designated locale or administrative district. The per capita data are disputed; reported values, along with their numerators and denominators (see Supplementary Table S1). The methodological implication is clear: an intervention targeting behavioral changes related to the physical aspects of a community must be assessed against explicitly defined baseline values, preferably using data obtained directly from primary statistical sources rather than secondary reports or summaries serving as background information for supporting key statistics.

Through the Qatar National Vision 2030 and the National Development Strategies (NDS), particularly NDS-1 (2011–2016), policies were implemented to raise the recycling rate from approximately 8%−38%, while restricting municipal waste generation to 1.6 kg per capita per day (Al Tamimi and Company, 2020). While the per capita waste generation reached approximately 1.3 kg/day, the intended 38% collection rate from the NDS-1 was not realized. Therefore, NDS-2 (2017–2022) set a new collection rate target of 15% for 2022 (Company 2020, 2022). The MSW treatment capacity is bolstered by the Mesaieed Domestic Solid Waste Management Center, which can process up to 2,300 tons daily. This study explores the behavioral and spatial elements related to how households separate materials prior to collection, emphasizing the community's role in shaping personal disposal choices.

1.1 The problem of urban leftover space (ULSp)

The rapid and poorly coordinated urban expansion of Doha (Rizzo, 2014) has led to a proliferation of unused or underutilized “leftover” spaces (Akkerman and Cornfeld, 2009), including building setbacks, undefined block edges, mosque-forecourt margins, market peripheries, and metro approaches. AL-Mohannadi et al. (2023) identify comparable remnants in Doha's Al-Najada Zone and propose their redesign grounded in social principles, showing the fragments possess latent civic utility and are open to intervention. The term leftover space is primarily used (equivalent to “residual space”), with “lost space” reserved for Trancik's (1986) interpretation. In the Gulf region, empirical research exploring people's perceptions of leftover spaces is acquiring traction, offering new insights into how these spaces are viewed. Azhar et al. (2022) studied the evaluation of urban leftover spaces (ULSp) by built-environment experts vs. laypeople, uncovering consistent disparities that point to the implicit opportunities of these spaces and the challenges of using only professional assessments. Such leftover spaces are seldom systematically and consistently assessed as potential sites for civic reuse or recycling infrastructure.

1.2 Immersive VR as a pre-deployment evaluation tool

Real-world pilots of street furniture are costly, require significant time, and present challenges in terms of control and management. Immersive virtual reality (VR) offers a controlled and consistent simulation environment that can be tested and refined before deployment. VR facilitates the alteration of diverse design components, simultaneously producing empirical behavioral metrics and introspective participant inputs. Previous studies have employed virtual reality to examine urban design in terms of pedestrian behavior (Oselinsky et al., 2023) and to conduct controlled assessments in engineering and educational settings (Halabi, 2020). However, the credibility of these findings is accompanied by specific limitations. VR possesses inherent biases, including the underestimation of egocentric distance and a narrowly defined concept of locomotion (Horejsi et al., 2025). Such biases may lead to errors in spatial measurements or in the approach to objects. This investigation treats VR-derived approach, gaze, and sorting measures as behavioral proxies, as indicators of what participants do within the immersive environment rather than direct measures of what people actually do in the physical world; these proxies serve as design discriminators and require confirmation through a subsequent physical pilot-validation stage.

1.3 Scope and contribution

Adhering to the PRISMA 2020 guidelines, this systematic analysis used a conceptual framework (Sections 2, 3) to guide and restrict the development of a proposed design-and-evaluation framework (Section 4), reserving empirical verification for future studies (Section 5.6). The findings of this review offer evidence, and the proposed culturally tuned virtual reality (CT-VR) framework and propositions present hypotheses derived from this evidence. The differentiation between these two will persist. In addition, we specify the exclusions from this study: it is not designed as a gamified environmental education initiative for minors, an ocean plastic awareness campaign, or a desktop serious game. Instead, the emphasis is placed on adults' recycling practices concerning the physical components of public recycling infrastructure within a realistic VR representation of the public realm. This distinction is noteworthy because current research on VR and environmental issues has predominantly focused on the categories previously excluded. The three research questions correspond to the review and synthesis (two) and the conceptual model (one). All align with the contributions.

• RQ1 (C1 and C2): How does the conceptualization of VR's role differ across the three identified literatures, where do their perspectives diverge, and what is the resultant systemic deficiency?
• RQ2 (C3): How can Islamic environmental ethics (Khalifa, Taharah) be quantified or used as measurable design parameters within a socio-spatial framework?
• RQ3 (C4 and C5): How can micro-scale civic recycling infrastructure be effectively assessed using VR coupled with validated instruments and objective tracking to support reproducible site prioritization within ULSp, distinguishing the VR behavioral-evaluation stage from the spatial site-selection stage?

C1 will be produced, serving as an integrated visualization of VR's role as perceived by three separate entities; C2 is a six-gap cross-silo matrix substantiated by the counts derived from the executed screen; C3, A Defensible Operationalization of Khalifa and Taharah as measurable design variables; and C4 is a measurement system that correlates objective tracking with validated measures within a theory of planned behavior framework. and C5, a replicable approach to Analytic Hierarchy Process (AHP)/Geographic Information System (GIS) site selection, accompanied by detailed examples.

1.4 Conceptual grounding: leftover space theory

Trancik's (1986) work, “Finding Lost Space,” supports the notion that interstitial fragments can be considered a potentially usable component, as it identifies lost spaces resulting from modernist urban planning, vehicular orientation, and single-use zoning. Rizzo (2014) demonstrated a comparable fragmentation of human scale concerning megaprojects in the Gulf region, while Azhar et al. (2022) identified a divergence in perceptions of urban leftover space (ULSp) from both professional and lay viewpoints. Therefore, an evaluation method that captures the perceptions of the public in situ, rather than depending solely on professional judgments, is needed.

1.5 Theory of planned behavior and the intention–behavior gap

The theory of planned behavior (Ajzen, 1991, 2020) is considered the leading model in recycling studies, highlighting attitudes, subjective norms, and perceived control as key determinants of an individual's intention to recycle. The intention and perception of control influence an individual's recycling behavior. The most pertinent facet of this theory is the intention-behavior gap (Kollmuss and Agyeman, 2002), as recycling intentions have consistently shown greater predictive power than reported recycling behavior. Chan and Bishop (2013) extended the theory of planned behavior's application to recycling, incorporating moral norms, which accounted for 39% and 41% of the variance in stated intent and actual recycling, respectively. While meta-analyses consistently validate the theory, they also underscore the gap between intent and behavior (Armitage and Conner, 2001; Bamberg and Möser, 2007). The conceptual foundation of this study acknowledges the discrepancy between behavior and intent, prioritizing objective measurements over self-reporting, as research shows that spatial factors significantly influence household waste disposal more than stated individual intentions (Rosenthal and Linder, 2021).

1.6 Islamic environmental ethics as design drivers

Two key Islamic concepts form the foundation of this study's research design. First, Khalifa states that humankind must act as a “steward” or “trustee,” fulfilling its “Amanah” by managing creation. Second, Taharah signifies the ritual purity and cleanliness that adherents of Islam endeavor to attain. Extensive scholarly work underpins these two concepts (Nasr, 1996; Dien, 2000; Foltz et al., 2003), with applications planned in domains such as waste management and environmental ethics and behaviors using Maqasid al-Shari'ah (Shompa et al., 2024; Begum et al., 2021; Miftahorrozi et al., 2022). However, no studies have been identified that have attempted to apply the concepts of Khalifa or Taharah to the design of specific recycling infrastructure within Qatar or other Gulf Cooperation Council (GCC) member states. This gap is addressed by C3 (Section 4.3). From a broader perspective, considerable evidence supports a pragmatic view of faith-based interventions. While these interventions might enhance public understanding of environmental responsibilities, they rarely result in behavioral modifications when encountering considerable political or economic restrictions (Zulkifli et al., 2023). This underscores the substantial value of establishing and validating a controlled pre-deployment method that facilitates the segregation of cultural design cue impacts from structural confounders.

1.7 Immersion and presence theory

Subjective presence, defined as the experiential perception of being physically present in a location, is a prerequisite for conducting a valid assessment prior to deployment, necessitating that users interact with virtual infrastructure in a manner comparable to their interaction with physical infrastructure. The Igroup Presence Questionnaire (IPQ; Schubert et al., 2001) is recognized as the preeminent instrument for measuring presence. Recently, the administration of all IPQ questionnaire items and the reporting of results via standardized scales have been recommended (Tran et al., 2024). Hence, the CT-VR framework interprets presence as a condition that requires assessment rather than one that is assumed. While the sense of presence is a significant factor in how immersive technologies affect user behavior, its direct contribution to the causes of immersion-related behavioral effects has not been established. The Behavioral Framework for Immersive Technologies (BehaveFIT, Wienrich et al., 2021) provides the mechanism and is employed with TPB, where TPB delineates the predictors of recycling, and BehaveFIT clarifies how the medium affects these factors.

To bridge the theoretical models (Figure 1) with the contextual realities faced by Gulf cities, including Doha, this study adopts a tripartite CT-VR framework that structures the analysis and sharpens the focus on the identified problem.

• The Problem: cities in the Gulf Region, including Doha, produce significant waste per capita due to high municipal waste generation yet have low recycling rates, alongside considerable unused urban space caused by rapid and unregulated petro-urban expansion and the elevated expenses linked to a “build first” rather than “deploy first” approach. The influence of engineering on waste management extends beyond technical mechanisms to encompass cultural interpretations.
• The Gap: the literature review indicated a lack of studies investigating the intersection of VR design assessment, pro-environmental behavior evaluation, and the assessment of ULSp (n = 0 out of 18 studies).
• The CT-VR Framework: the design incorporates a stationary kiosk chassis with customizable skins reflecting various cultures, representing Khalifa (stewardship) and Taharah (purification).

2 Methods

The review was conducted and reported according to the PRISMA 2020 guidelines for reporting reviews (Page et al., 2021). The method is elaborated in Supplementary File S2, and the review's procedural overview is depicted in Section 3.1. The subsequent sections adhere to the standard method for systematic reviews, presenting information in the review's sequence process: study design, review question and PICOS, participants, interventions, comparators, search strategy, data sources, study selection, data extraction, and analysis. Section 4 establishes the conceptual CT-VR framework, and Section 5.6 highlights areas that may require empirical confirmation of the proposed model.

2.1 Study design

A systematic review was used in this paper's literature review to develop a narrative, cross-disciplinary synthesis. Given the varied nature of the study designs, settings, and outcomes across the three disciplines contributing data to this publication, a meta-analytic review was deemed unsuitable and therefore excluded from the outset of the research initiative. The findings from the extant literature are presented through a narrative synthesis, employing a structured gap analysis (Section 3.3) as both an analytical instrument and a method for assessing robustness to bias.

2.2 Review question and PICOS

This study aimed to reveal the extent to which immersive VR has been used by researchers to assess culturally specific recycling programs and comparable urban micro-infrastructures in ULSp, incorporating both objective and subjective evaluation techniques. This study used PICOS parameters such as

• Population (P): adults (or, where relevant, general users) interacting with civic recycling or analogous micro-scale infrastructure and ULSp in which such infrastructure is located.
• Intervention (I): immersion in virtual reality environments, whether through head-mounted displays or CAVEs, is employed as a method for testing and eliciting behavior to assess designs influenced by cultural or religious factors.
• Comparators (C): where relevant, comparators may encompass desktop/2D presentations, conventional presentations, neutral vs. tuned design options, or baseline/no intervention comparisons. Given the variety of eligible designs, comparators were deemed unnecessary.
• Outcomes (O): measurement of behavioral indicators (proxies for approach, dispensing, gaze, and attention), user presence and experience, components of the Theory of Planned Behavior (attitudes, norms, perceived control, intentions), and the moderating role of cybersickness on data quality during VR use (cybersickness is an established concern in VR that may affect the precise measurement of approach/ dwell times).
• Study Design(s) (S): the original pool of studies was refined by excluding non-peer-reviewed records, retaining peer-reviewed experimental, quasi-experimental, observational, mixed-methods, and design evaluation studies, while reviews were separated from the pool.

2.3 Participants

Eligible studies included humans interacting with a physically built environment, civic infrastructure, or VR representations of those environments; no age or population restriction was applied beyond each study's own scope. As noted in Section 3.2, diverse studies have used student samples to generalize their findings to other populations. Studies on non-human or purely simulated agents were excluded.

2.4 Interventions and comparators

This study primarily focused on evaluating the design intent of an immersive VR experience. Studies employing VR for training, therapeutic, or educational purposes without an evaluative or design component. Awareness studies were omitted because, although environmental awareness was acknowledged as a precursor to behavioral intention, it was not the direct focus of the research. The primary aim of this research was to examine the physical dimensions of infrastructure before implementation, thus assessing individuals' documented approaches and disposal habits in relation to infrastructure, as opposed to alterations in their knowledge or attitudes. Designs that enhance awareness, such as those employing gamification or educational methods and typically relying on self-reported intentions, address a different connection in the behavioral sequence. Thus, they are addressed in Section 3.2.2 with a descriptive summary, distinct from the data collected for this study. Documentation of the comparator conditions was optional, reflecting the variety of potential study designs and the review's focus on describing variable relationships rather than compiling results.

2.5 Search strategy and data sources

The evaluation encompassed six databases: Scopus, Web of Science, IEEE Xplore, ScienceDirect, ACM Digital Library, and PubMed. A thorough search of all six elements was performed by leveraging three Boolean constructs: immersive technology, pro-environmental behaviors and infrastructure, and urban leftover spaces (ULSp), and site assessments. The search strategy involved an “AND” operator to link these categories and an “OR” operator for conditions within each category. The study covered the period from January 2015 to April 2026 (the search was executed in April 2026; see Supplementary File S1 for database-specific final search strings and exact execution dates), incorporating notable pre-2015 contributions by Mehrabian and Russell (1974), Norberg-Schulz (1980), Trancik (1986), and Ajzen (1991). Specific searches within the database encompassed Islamic-environmental-ethical terminology (“Khalifa,” “Taharah,” “Maqasid”), terms employed when conducting searches. The complete search queries and associated dates are listed in Supplementary File S1.

2.6 Eligibility criteria

Studies were deemed eligible if they utilized an immersive Virtual Reality (VR) approach, such as head-mounted displays or CAVE systems, as their primary research method for assessing design or investigating environmentally beneficial behaviors. This also extends to the evaluation or prioritization of urban leftover spaces (ULSp) within that context. The other inclusion criterion was that the studies had to be peer-reviewed and written in English. Studies that used desktops alone or only used Augmented Reality with no immersion factor as part of the study design were excluded. Similarly, non-peer-reviewed publications, including theses, preprints, and editorials, were excluded. Reviews and meta-analyses were excluded from the initial list but were documented independently. Thus, the inclusion/exclusion criteria provided the PICOS elements specified in Section 2.2. Although the three silos share the immersive-VR eligibility requirement above, they were searched with silo-specific facets (Supplementary File S1): the design-evaluation and pro-environmental-behavior silos required immersive VR as the primary method, whereas the leftover-space silo used the spatial and site-assessment facet (Block C) with immersive VR as an optional facet, because the ULSp literature is not predominantly VR-based. One leftover-space study is therefore retained without an immersive-VR component and is clearly identified as such. Because the cross-silo gap matrix (Section 3.3) asks whether any single study simultaneously satisfies criteria drawn from all three silos, the pooled corpus of 18 studies is used as a common denominator; the zero-count intersections are reported as bounded observations about this retrieved corpus rather than as claims determined solely by the search construction, and this dependence on the search strategy is stated as a limitation in Section 5.2.

2.7 Study selection, data extraction and analysis

In the screening process, duplicate records were identified, and all records were independently reviewed by two reviewers for eligibility at the title/abstract and full-text levels. Cohen's Kappa was employed to quantify agreement among reviewers, showing substantial concordance across both screening phases [Title/Abstract: κ1 = 0.78, 95% CI (0.65, 0.92); Full Text: κ₂ = 0.76, 95% CI (0.55, 0.98)]. Upon reviewing studies that met the eligibility criteria, two individuals extracted key bibliographic information, including the silo, VR medium, population/sample, study design/comparators, measurement type (behavioral, presence, self-report), and whether the authors had culturally adapted their intervention and selected a reproducible site. Data from the studies populated the gap matrix (Section 3.3) in this study.

The synthesis was presented in a narrative format, focusing on the three “silos” described in Section 3.2, with a cross-silo gap matrix ranking all included studies by six criteria (Section 3.3). Methodological quality and risk of bias were assessed using a set of design-appropriate instruments rather than a single tool. The Mixed Methods Appraisal Tool (MMAT), developed by Hong et al. (2018), was used for qualitative, quantitative descriptive, and mixed-methods studies. The risk of bias was appraised with design-appropriate tools. Because the included corpus comprised experimental and quasi-experimental design-evaluation studies, pre/post behavioral studies, and one governance study, but no randomized controlled trials, non-randomized studies of interventions were appraised using ROBINS-I (Sterne et al., 2016) and qualitative, quantitative descriptive, and mixed-methods studies were appraised using the MMAT (Hong et al., 2018); RoB 2 (Sterne et al., 2019) would be applied to any randomized controlled trial, but none met the eligibility criteria. These appraisals were integrated into the synthesis through a structured risk-of-bias assessment. In this process, studies identified as having a risk of bias were excluded from the analyses to determine the effect of their removal on the gap size (Section 3.3). Owing to the heterogeneity issues detailed in Section 2.1, no meta-analyses could be performed. Supplementary File S4 contains the appraisal results pertinent to this study.

3 Results

3.1 Study characteristics and flow diagram

A total of 194 records were retrieved from the databases. After excluding 86 duplicate entries, 108 distinct records were identified. The screening of 87 unique records by title and/or abstract was conducted after the removal of 21 additional non-scholarly or otherwise ineligible records. Of these, 53 were deemed ineligible. 34 full texts were examined, and 16 were excluded based on the criteria shown in Supplementary Table S3 and Figure 2. Because of these exclusions, 18 (N = 18) studies were included in the synthesis. The parameters for study inclusion were deliberately set to prioritize peer-reviewed, indexed, and English-language materials that incorporated Immersive VR. This approach specifically targets research pertinent to ULSp, and the implications of these constraints are thoroughly examined in Section 5.2.

3.2 Study characteristics and synthesized findings

3.2.1 VR for architectural and environmental design evaluation

Immersive VR has proven effective in evaluating architectural elements, street furnishings, and overall urban landscapes. Immersive VR presents an innovative method for laypersons to evaluate designs (Ma et al., 2025) and contributes to research on occupant comfort and adaptive behavior (Alamirah et al., 2022). At an urban scale, research has shown its validity for multisensory assessment (Maffei et al., 2015), comparison of user preferences between VR and traditional communication methods (Zhu et al., 2021), citizen perceptions of streetscape safety (White et al., 2023), citizen assessments of public space quality (Belaroussi et al., 2024), and testing walkability and design of future streets (Oselinsky et al., 2023; Argota Sánchez-Vaquerizo et al., 2024). This highlights the importance of Building Information Modeling (BIM)-VR studies for the validity logic, as they have proven a high correlation between virtual and real-world visual perception, with eye-fixation patterns aligning to within roughly 1.5% (Hermund et al., 2018).

Galán Serrano et al. (2024) conducted an evaluation of street furniture using a head-mounted display, incorporating eye-tracking data, a subjective sense of presence measurement tool, and a semantic differential self-reporting method, all focused on one piece of civic furniture. This study is unique within this dataset because it integrates all three micro-level methods. It also pioneers the application of these methods to civic furniture units, deviating from waste management units, and does not incorporate cultural considerations. Primarily, the research data were collected at the building or street level. In contrast, a few studies, specifically 3 out of 18, incorporated an immersive technique for the evaluation of micro-level civic infrastructure (Section 3.3).

3.2.2 VR for pro-environmental behavior, recycling and waste

The study by Stenberdt and Makransky (2023) serves as a prime example of an intervention involving immersive waste sorting aimed at school-based climate change education, which enhanced participants' knowledge and pro-environmental intentions. Self-efficacy served as a predictor of the participants' intent to sort. The study focuses on sorting waste into fields within a school environment, rather than adults' interactions with a physical structure, which inherently highlights the research gap. Plechatá et al. (2024) also reported that direct experience with dietary information via VR fostered stronger behavioral intentions and actions compared to passively receiving that information within the VR environment. Mediating these findings, efficacy beliefs highlight VR's distinct experiential and evaluative significance, setting it apart from mere information provision and connecting it to dietary compared to structural/infrastructure behaviors. The two additional studies exemplified VR-as-training and VR-as-awareness design models, and the seminal literature review (Cosio et al., 2023) suggested that environmental extended reality research was expanding significantly, although evidence of behavioral impacts remained limited. To reconcile these studies with the full-text exclusion of awareness, communication, and edutainment applications (Supplementary Table S3), a distinction is drawn between studies included in the formal synthesis and studies discussed only as contextual literature. Educational, gamified, and training-oriented VR studies were retained in the behavioral silo only where they immersively operationalized waste-sorting or disposal actions as measured outcomes; studies whose sole function was awareness or communication were excluded from the synthesis and are cited here for context only. Each such study is flagged accordingly in Supplementary File S4 so that the synthesized set is clearly separable from the contextual set.

Recent research has revealed a growing number of new virtual reality (VR) applications designed for waste sorting. Peng and Leong (2024) used VR to simulate waste sorting, revealing that participants subsequently reported a greater willingness to sort waste and a better understanding of the process, as evidenced by a pre- and post-intervention comparison involving 250 residents (Borawska et al., 2024). While these studies showcase the promise of VR in waste management, they distinctly highlight the differences between this research and previous work. These findings stem from questionnaires that gauged participants' self-reported knowledge and intentions regarding waste sorting within an educational setting, as opposed to observing their actual behaviors following modifications to the physical recycling infrastructure. Thus, the significance of this research, as evidenced by the corpus gathered (Section 2.6), is clear, yet it falls short of being a comprehensive survey of the literature. The pre-deployment, instrumented evaluation of recycling infrastructure remains a crucial, unaddressed aspect, along with the practical implementation of Islamic environmental ethics as adaptable design elements.

The meta-analysis findings might moderate the optimism regarding VR's persuasive capabilities. A comprehensive analysis of 43 studies involving 5,644 participants, conducted by Martingano et al. (2021), revealed that while virtual reality exhibited a notable effect size (d = 0.33) for improving emotional empathy, it did not have an effect size (d = 0.08) for improving cognitive empathy and did not improve on lower-technology options like reading. The CT-VR framework benefits most from VR, not for its superior persuasion, but for its capacity to facilitate consistent, tightly controlled, and measurable pre-deployment trials. This silo is dominated by gamified education, training, and awareness, sampled from students and special populations, and drawn predominantly from Western and East-Asian settings; only 1 of 18 studies immersively pre-tests recycling infrastructure (Section 3.3).

3.2.3 Urban leftover spaces (ULSp) and their assessment

Garau et al. (2025) employed Space Syntax and GIS-based prioritizing to develop rigorous, replicable methodologies for transforming underutilized street spaces into social areas, notably excluding formal AHP and VR-based approaches. Rizzo (2014) and Furlan et al. (2022) conducted thorough characterizations of the Gulf Record, yet their analyses omit a detailed pre-deployment method and a reproducible framework for behavior-tied site prioritization. AL-Mohannadi et al. (2023) investigated urban voiding within Doha's Al-Najada Zone, subsequently proposing re-planning scenarios rooted in social contexts. These scenarios highlighted both local relevance and a desire for intervention, although they did not include an evaluative method to assess the impact of a designed insertion on the usage. This CT-VR framework provides methodological steps, with Section 3.2.2 confirming that the silo utilizes VR for visualization rather than an instrumented evaluation. No studies were identified in the reviewed literature that proposed an immersive pre-deployment evaluation method for ULSp. Furthermore, none of the reviewed studies combined formal GIS-MCDA/AHP site selection with an immersive pre-deployment technique (Section 3.3).

3.3 Synthesized findings: cross-silo gap analysis

A collective review of the three syntheses (Table 1, Figure 3) revealed that each source contained unique information absent from the remaining two. While design-evaluation VR uses rigorous instrumented techniques, it neglects micro-infrastructure and culture. VR for behavior change holds great cultural value, yet it uses gamified designs based on non-inferential methods sampled from students. The concept of “leftover space scholarship” shows spatial depth but lacks a defined evaluative method. The six identified gaps were quantified using data from 18 studies, and the sensitivity analysis involved recalculating each count after removing the studies with a substantial risk of bias. The outcome is a statement that functions as a bounded observation compared to a defined corpus, rather than an all-encompassing negative claim (Section 5.2). Even within broad boundaries, the intended results are empty or almost entirely so.

Table 1. Cross-silo gap matrix with n/N counts.

Gaps (d) and (f) stand at 0/18 and are invariant to exclusions (see Section 3.4 for the sensitivity analysis).

3.4 Assessment of risk of bias (RoB)

Each study was appraised with a design-appropriate risk-of-bias or quality tool (ROBINS-I for non-randomized studies of interventions and MMAT for qualitative, quantitative descriptive, and mixed-methods studies; no randomized controlled trials were included, so RoB 2 was not required; respective ratings detailed in Supplementary File S4). Both primary gap cells (d): Cultural/Religious Tuning and (f): Reproducible GIS-MCDA/AHP Site Selection were excluded from consideration. For the two primary zero-count gaps (d and f), the numerator is zero and cannot change under exclusion. For the remaining gaps, removing studies with a high risk of bias alters both the denominator and the composition of an already small corpus, so the direction and magnitude of any change in the observed proportions cannot be assumed in advance. The results of the sensitivity analysis are therefore reported transparently in Supplementary File S4, once the appraisal of every included study has been completed, rather than anticipated here.

4 A culturally tuned CT-VR framework

This research is motivated by gap analysis, leading to the central contribution of a CT-VR framework (Figure 4) suggesting the use of VR for evaluating a recycling kiosk before its actual construction. The CT-VR framework posits the recycling kiosk as a culturally and spatially embedded behavioral catalyst. This allows for the real-time modification of design elements in virtual reality, facilitating the evaluation of user reactions to changes. The application of VR goes beyond simple demonstrations, offering a way to meticulously control and assess cultural nuances, light levels, and object placement, as behavior is recorded objectively. The CT-VR framework includes four key elements: classification of ULSp, collection of VR-adjustable, culturally specific design parameters, a testable theory of action, and a logical approach to measurement designed for VR sessions. Each is linked to a particular gap identified in earlier research (Section 4.1) and presented as a falsifiable hypothesis, with the empirical testing procedures detailed in Section 5.6.

4.1 From identified gaps to design choices

All design decisions can be attributed to a particular gap identified during the review (Section 3.3, Table 2), not simply to an unsubstantiated claim. The gaps were: (a) VR used for teaching, not evaluation, and (b) the neglect of micro-scale infrastructure, the kiosk framed as a design object. The assessment was conducted at the scale of the receptacle and its surroundings using the skin-swapping design space (Section 4.3). A measurement framework is applied that prioritizes behavior, not learning, as the definitive result (Section 4.5); (c) there were no immersive pre-deployment tests motivated by the framework's pre-deployment focus and Proposition P1; (d) the absence of cultural or religious tuning (0/18) constitutes its defining characteristic, with Khalifa and Taharah being conceptualized as manipulable indicators (P1, P3); (e) fragmentary measures (1/18) motivate the three-channel measurement logic (P4); and (f) ad hoc site selection (0/18) uses the reproducible AHP/GIS method (P5).

Table 2. Established findings in the literature vs. new contributions by element.

From the synthesis, two cross-cutting options emerge rather than from a single decision: the climate-responsive shading variable (Proposition P2), driven by the Gulf city context in Section 1.1–1.3, and the empirical consideration of presence as a mediator (Proposition P6), stimulated by the presence theory literature in Section 1.7. The overall CT-VR framework (Figure 3) highlights how manipulable design cues (Khalifa, Taharah) and non-religious controls (climate-responsive shading, salience) influence disposal behavior within an immersive VR environment and the typology influencing these pathways, as well as the location of each proposition (P1-P6) within its projected routes to be tested, not validated.

4.2 Five leftover-space typologies

The first component of the CT-VR framework recognizes the ULSp of a Gulf city in five typologies, each conditioning both the appropriate design and the behavioral prediction to be tested. Table 3 presents a university typology as one of five distinct settings, contrasting with the common convenience samples used in VR research. Participant age and education were incorporated as covariates, allowing for the isolation of setting-specific effects from variations in population characteristics.

Table 3. Five leftover space typologies and their predicted behavioral conditioning.

4.3 Operationalizing Khalifa and Taharah as design variables

The second part of the CT-VR framework defines the design space not as a finished product but as a collection of variables that can be measured and changed. Two cultural cues from Islamic environmental ethics—Khalifa and Taharah— were paired with two non-religious controls (climate-responsive shading and salience), ensuring that cultural influences could be measured against equivalent baselines. This study proposes this operationalization with caution, presenting it as a hypothesis for validation rather than a concluded finding. Khalifa (trusteeship over creation) is translated into a stewardship-framing cue that casts correct disposal as discharging an entrusted responsibility, and Taharah (purity) into a cleanliness-and-separation cue. Integrating an ethical-religious principle as a design parameter necessitates the translation of abstract concepts into tangible directives that are expected to influence behavior, with a critical distinction maintained between superficial implementation and genuine ethical substance. When fully understood, Khalifa (trusteeship over creation) and Taharah (purity) represent communal and structural principles rather than motifs; the framework does not instantiate depth in a bin skin. With its narrower, defensible design, it can provide an in-situ prompt of the user's ethical beliefs, smoothing the gap between their values and disposal choices. A stewardship-framing cue derived from Khalifa conveys the principle of the trusteeship of creation as guidance on proper item disposal to fulfill fiduciary duties. Similarly, cleanliness/separation cues based on Taharah translate the principle of purity. Each is linked with a directional, falsifiable prediction (Section 4.4), which ensures that the operationalization is testable instead of interpretive and acts as a supplement, not a substitute, for the communal and educational processes through which these ethics are developed. Whether such cues influence behavior and whether any effect results from cultural framing rather than mere salience remains an empirical question that the design does not resolve and that the neutral-cue controls aim to address. To establish construct validity, the framework specifies that the intended meaning of each cue be verified before behavioral testing: prior qualitative co-design and manipulation checks with members of the local population are required to confirm that participants perceive the stewardship cue as invoking Khalifa and the cleanliness/separation cue as invoking Taharah. To distinguish specifically religious or cultural effects from more general moral or cleanliness priming, the design further specifies that each religiously framed cue be compared not only against a neutral condition but also against a secular counterpart of equivalent content, that is, the Taharah cue against a secular cleanliness message and the Khalifa cue against a non-religious stewardship or responsibility framing. The culturally diverse composition of Gulf populations is acknowledged, and cultural response is not treated as homogeneous; participants' cultural and linguistic backgrounds are therefore modeled rather than assumed constant. The direction and behavioral influence of faith-related cues is treated as a hypothesis to be tested rather than presumed, consistent with evidence that religiosity and Islamic religious values are associated with pro-environmental behavior in Muslim urban contexts (Rice, 2006), and with precedents for embedding immersive technologies within religiously and culturally specific urban settings (Ebraheem et al., 2025).

The CT-VR framework embeds three safeguards to prevent the instrumentalization of faith or implied endorsement when operationalizing religious values in public design. Shared ethical values, such as stewardship and cleanliness, are evoked by cues, not religious texts or imagery. The cultural sensitivity criterion for site selection (Section 5.6.3) and stakeholder consultation is mandatory, not elective, and this study acknowledges as a limitation that local religious experts and users were not consulted during the present framework-development phase; their participation is a required condition of any future application and would strengthen the cultural grounding of the operationalization, and neutral-cue control guarantees that any claim about religious cue effectiveness is tested against an equivalent baseline. These guardrails are a vital contribution, ensuring that the operationalization is usable while preventing its inherent risks. As Dane et al. (2024) show, immersive VR has functioned as a collaborative medium for co-designing public spaces, embedding stakeholder engagement deeply within the design stages rather than treating it as an afterthought.

The other parameters govern the design of the space. A climate-sensitive shading variable acknowledges that in extreme heat conditions, such as those in Doha, offering shade does not affect a user's decision to approach the bin. Given that the shading variable is independent of the type of cue presented, the effect of the religious cue can be isolated and scrutinized (Proposition P2). The constraint of using four bins guarantees that the design aligns with the practical operational conditions of Qatar's many active recyclers, ensuring both internal validity and feasibility of implementing any subsequent recommendations. These choices are grounded in the evidence review. Salient bins attract more attention and are used more often, although color preference varies according to the setting and material (Högberg and Sörqvist, 2026). Bin usage tripled when general waste bins were accessible (Rosenthal and Linder, 2021, N = 272), and involving users in bin design enhanced their acceptance (Keramitsoglou and Tsagarakis, 2018). As color and iconographic conventions differ across cultures, Western approaches should not be automatically applied in a Qatari setting, emphasizing the need for culturally adapted solutions rather than simple adoption.

4.4 A falsifiable theory of action

The third part of the CT-VR framework specifies the impact of design variables on behavior using six testable propositions (Table 4), each corresponding to an unoccupied or scarcely filled cell within the gap matrix (Table 1), thus preventing validation by mere assertion.

Table 4. Six falsifiable propositions linking design variables to behavioral outcomes, each mapped to a gap matrix cell.

4.5 The measurement logic

The fourth component of the CT-VR framework is its measurement logic. This study detailed a principled approach to measuring its constructs through three interconnected channels: objective behavioral tracking, validated self-reports, and a presence check, all of which correspond to the established constructs of the TPB. To avoid an over-extended battery, a limited set of primary outcomes is pre-specified, the aim behavioral proxies and the TPB battery, with affect (PAD), user experience, cybersickness, and usability treated as secondary or control measures within a stated statistical hierarchy (Supplementary Table S4). Presence is assigned a single, pre-specified analytic role for each analysis rather than functioning simultaneously as a validity threshold, exclusion criterion, manipulation check, and mediator; where it is used as the mediator for Proposition P6, that role is fixed in advance. Because mediation and structural-equation models are planned, a sample-size and power justification will be established a priori before data collection. Because of the intention–behavior gap (Section 1.5), where stated intentions often overestimate actual behavior, objective measures are prioritized, and self-reports are used only for confirmation. The implementation of this logic is detailed in the empirical program provided in Section 5.6 (Supplementary Table S4). However, the two levels are kept clearly apart through mapping. The first is measurable: gaze duration, fixation counts, and time to first fixation are recognized indicators of the attention approach, and selecting the correct bin for a stimulus serves as a direct behavioral measure. For example, Li et al. (2026) presented a large-scale example using virtual reality and physiological sensors with 251 street-scene images. The second hypothesis proposes that these measurable indices might predict TPB's constructs of attitudes and perceived behavioral control (P4), showing a potential link. The CT-VR framework proposes a testable perspective, in contrast to assumed knowledge. This is a sound viewpoint, as attention and approach are recognized as theoretical precursors to intentions, and small-scale spatial configurations often provide more exact predictions of waste disposal behavior than individuals' stated intentions (Rosenthal and Linder, 2021). Presence is a conditional determinant for measurement, and VR-to-real predictive validity is unestablished (Section 5.2).

5 Discussion

5.1 What the foundation establishes

This systematic review and framework offer a novel combination of three elements. The first quantitative synthesis revealed no interrelationship between individuals who assess immersive designs, adjust cultural practices, and establish recycling systems, as shown by the analyzed corpus (Table 1). This observation reflects a finding rather than a flaw and firmly underlines the value of this research. The second part is a conceptual framework encompassing typologies of leftover space, adaptable cues for interactive elements, and integrating Khalifa and Taharah as design parameters. This CT-VR framework reconceptualizes the conventional “recycling bin” as an artifact with significant behavioral, cultural, and spatial attributes. Finally, the method (i.e., measurement architecture + multi-criteria site selection) is replicable and transferable, independent of the VR-based study (Table 5). Given the absence of validation from empirical data, the framework's claims function as hypotheses, subject to the research outlined in Section 5.6, rather than confirmed findings. Therefore, the gap counts should be regarded as an observational limit of the search rather than assertions about the entire field (Section 5.2).

Table 5. Site selection criteria, rationale, and AHP weights.

The weights shown are illustrative and consistent with the example in Supplementary Table S5.

5.2 Limitations

This study has three limitations that confine the scope of its contribution.

• The synthesis is limited by the defined scope of the research and the breadth of the literature reviewed. This study was restricted to peer-reviewed articles published in English and excluded gray literature, regional publications, works not indexed in databases, and literature written in Arabic or other non-English languages. Hence, the synthesized subset of the literature was a lower bound. The assertion about the “near empty” intersection is still valid because of this constraint, as the sensitivity analysis in Section 3.4 safeguards against overreliance on low-quality evidence, and no studies were found for the two gaps of interest.
• The link between objective tracking and TPB is partially hypothetical and is examined in Section 5.6. The correlation between virtual reality experiences and real-world events has not yet been proven. Studies are currently examining whether virtual reality can produce valid ecological perceptions of the environment (Sato and Higuchi, 2025). Therefore, presence served as a measure besides the assumption of its existence as a quantified condition (Section 4.5).
• The study centers on a single city and faith framework, while the transferability of the mechanism is detailed in Section 5.3. The data for calibrating cue content and weighting were derived from a predominantly Muslim Qatari context and should not be assumed to generalize without recalibration.

5.3 Generalizability beyond Doha and Islamic contexts

The framework's design prioritizes transferability, although its portability depends on several factors. The transferable elements encompass structural aspects (factor typology as a factor, skin-swapping control, AHP-weighted site selection, and three-channel measurements) as these are content neutral. However, culturally specific content remains untransferable. This encompasses the expected impacts of the Taharah and Khalifa cues, which were specifically designed for a Muslim-majority Qatari demographic. Thus, a more precise specification is required to establish the applicability of this study to alternative environments. For instance, a researcher intending to apply this study in a diverse cultural context must establish a comparable framework grounded in local cultural values concerning stewardship and cleanliness, incorporate input from local experts to derive new weights for site selection via AHP, and validate all associated assumptions. Therefore, this study contributes a reusable method for determining the recycling infrastructure for each leftover space, exemplified by the Gulf and Muslim-majority applications addressed.

5.4 Theoretical implications

The conceptual framework encompasses three distinct actions.

• The primary contribution is an integrative framework that combines immersive design evaluation (Neo et al., 2021), pro-environmental behavior studies (Scurati et al., 2021), and “leftover space” discourse, unified by a single subject. Within cultural and spatial contexts, the recycling kiosk offers a common framework (typology, interchangeable visual cues, and three-channel measurement) and serves as a prototype for addressing micro-scale civic artifacts as design objects, psychological stimuli, and components of urban form.
• The CT-VR framework enhances environmental ethics theory by converting the rich normative concepts of Khalifa and Taharah (Dien, 2000; Foltz et al., 2003; Nasr, 1996) into measurable and manageable design components with associated falsifiable hypotheses. This facilitates the expansion of Islamic environmental ethics into empirical design research while simultaneously enriching secular design and behavioral literature with culture-specific insights.
• The CT-VR framework builds upon the TPB by integrating the intention–behavior gap (Kollmuss and Agyeman, 2002) as a central design philosophy, emphasizing empirical indicators of behavior and viewing presence as a mediator linking cues to behavior, a connection that has not yet been rigorously defined in the existing literature.

5.5 Practical implications

The CT-VR framework can be employed before validation. For municipal authorities, it redefines procurement (which bin to purchase) as design and siting (which culturally adapted configuration will be used in which residual setting), focusing on areas often neglected by master planning (Rizzo, 2014; Azhar et al., 2022) and providing a verifiable, criteria-and-weight-based site-selection framework (Section 5.6.3) instead of arbitrary placement. For institutional custodians, such as mosque, market, university, transit, and compound managers, the typology model offers tailored guidance specific to their respective environments. This includes employing stewardship and purity framings in proximity to mosques, focusing on capacity and proximity within markets, and emphasizing salience in transit environments. Section 4.3 provides crucial guardrails that delineate the boundary between ethically framing concepts and the inappropriate use of sacred iconography. For operators and designers, skin swapping entails maintaining a consistent, robust four-bin chassis while modifying low-cost surface treatments based on the usage context, ensuring economic viability and interoperability for Qatar's operators. There is one main cautionary point that the CT-VR framework requires validation. The intention is to guarantee that decisions about design and placement are conscious, clear, and culturally fitting, rather than prescribing the scale of their influence.

5.6 Future directions: an empirical research program

The CT-VR framework was built specifically to facilitate testing. This section details the process by which this will be accomplished. This paper proposes a research program rather than an experimental one. Thus, three immediate actions can stem from the gap analysis and framework: using immersive VR to validate design propositions, establishing a site-reproducibility method for technology testing and deployment, and duplicating the physical pilot study in a different context.

5.6.1 Immersive VR validation of the CT-VR framework

The most direct form of testing is through an immersive VR experiment that operationalizes the design space specified in Section 4.3 and assesses the six propositions (Section 4.4) as formal hypotheses. Virtual reality serves as the natural medium by enabling the manipulation of cue framing, salience, and shading while maintaining constant bin geometry, capacity, and placement through skin-swapping control, and it records objective proxies such as approach, dwell, correct-bin selection, and gaze, besides validated self-reports. Implementing a balanced design, wherein adults are assigned to specific scenarios based on typology and cue configuration, would allow for the conversion of P1–P6 into directional hypotheses that are amenable to falsification.

5.6.2 The measurement logic, instantiated

Implementing the measurement logic (Section 4.5) necessitates a battery capable of capturing the three channels without becoming an uninterpretable amalgamation of data. Supplementary File S3 and Supplementary Table S4 presents a structured example: objective tracking and the TPB battery as primary outcomes; affective response (PAD) as a secondary process measure; presence (IPQ) as both a validity prerequisite and the mediator for P6; and user experience, cybersickness (CSQ-VR, favored over the simulator-era SSQ), and usability instruments as controls and data quality checks. The decision to present the battery separately from the framework itself allows for the conceptual contribution to be delineated from any single, empirical implementation.

5.6.3 A reproducible site-selection method

The choice of where to test and eventually deploy must be planned carefully and not handled in an ad hoc manner (f, gap 0 of 18). A method for testing candidate ULSp is introduced using a reproducible process that ensures consistency. ULSp were ranked using a multi-criteria score called S_i = Σ_j w_j · x_ij, where x_ij is the rating of site i on a scale of 1–5 for criterion j, and w_j is the assigned weight for each criterion. This integrates the AHP (Saaty, 1980) with the GIS-MCDA weighted linear combination, a method validated for facility siting (Ali et al., 2023; Osséni et al., 2023). The weights reported here are illustrative rather than empirically elicited; the pairwise-comparison matrix in Supplementary Table S5 is derived from a predetermined weight vector and is perfectly consistent (CR = 0) by construction, which is pedagogically useful but is not equivalent to an elicited AHP model. In the planned application, the six criteria will be weighted through expert pairwise comparisons on the 1–9 Saaty scale (Saaty, 1980). Experts will be purposively recruited across the relevant municipal, planning, and community-stakeholder domains; individual pairwise matrices will be aggregated using the geometric mean of judgments; each matrix will be retained only if its consistency ratio is below 0.10; and rank stability will be examined through a sensitivity analysis that perturbs the criterion weights. With a written rubric as their guide, at least two raters will evaluate each rating and subsequently harmonize their conclusions.

A hypothetical illustration of this method, with three fictional candidate site examples and weighted vectors, is provided in Supplementary Table S5. The process detailed here serves to differentiate between candidate sites rather than recommending actual sites. The “degree of residuality” quantifies how strongly a location exhibits the defining traits of leftover spaces, characterized by their undefined purpose, vague spatial boundaries, and peripheral placement within their built surroundings (Trancik, 1986; Azhar and Gjerde, 2016). In practice, site A, B, and C are concrete examples of locations falling under the five typologies, such as the edge of a mosque's grounds, the perimeter of a marketplace, or the area near a metro stop. These specific spots were assessed based on the criteria previously described. For example, Site A has an advantage of 0.75 (i.e., 4.25 vs. 3.50) because of the high values assigned to “foot traffic” and “cultural sensitivity,” which were weighted higher than all other criteria (Supplementary Table S6). It is reasonable to assume that an alternative weighting method would yield the same results, which underscores the critical importance of sensitivity analyses. The method presents a self-contained, transferable, and agile framework suitable for site assessments in cities predominantly in the Gulf region and Muslim-majority countries, accommodating pilot initiatives, virtual reality research, and in-person trials with local weight considerations.

The framework extends beyond VR validation by prompting the engagement of human pilots at residual sites to confirm whether the phenomena identified through VR measurements are pertinent to real-world waste management. Further research is required to establish the predictive validity of these results. For instance, this research necessitates getting approval from the Institutional Review Board (IRB) for employing any biometric data collection techniques, such as eye tracking (gaze), head or body motion capture technologies, and similar methods. In addition, it is imperative to get explicit consent from participants, ensure secure data storage through encrypted access, implement the deidentification or anonymization of all collected data, and pre-register all data retention frameworks. Cybersickness (CSQ-VR) and immersion (IPQ) were recorded during each pilot session as quality control metrics, facilitating the interpretation of subsequent behavioral metrics within the context of their originating immersive environment.

6 Conclusion

This study contributes a VR-based method, coupled with the CT-VR methodological framework, to pre-evaluate culturally adapted recycling infrastructure within the ULSp of Gulf Cities. Systematic reviews revealed a distinct deficiency, as no studies were found that employed pre-implementation evaluations using objective immersion metrics to appraise the cultural calibration of recycling facilities, nor did any studies incorporate Islamic environmental tenets as design parameters to shape disposal behavior. The contribution of this research will be substantiated by evidence, in addition to rendering the absent methods explicit and reproducible. The CT-VR framework enables the controlled evaluation of culturally tailored recycling infrastructure prior to implementation, a capability currently absent in both urban design and waste management research methods literature. Examining how culturally informed recyclable variations influence disposal behavior under fixed geometric and locational conditions will yield both objective indicators and subjective self-reported actions, enabling site selection via a repeatable procedure. These six hypotheses, along with the framework, are offered as testable conjectures rather than confirmed discoveries. Further research should aim to empirically validate these results. By delineating the evidence-based findings from the framework's implications, this study offers a methodology that can be disseminated throughout the urban sustainability sector to identify optimal locations for recycling facilities.

Generative AI statement

The author(s) declared that Generative AI was used in the creation of this manuscript. The author(s) declare that the Pro writing aid tool was used during the preparation of this manuscript for language refinement and editorial assistance only. All conceptual contributions, methodological designs, data extraction and scoring, analyses, interpretations, and syntheses are the original work of the author(s), who take full responsibility for the content of this publication.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/frsc.2026.1925375/full#supplementary-material

Supplementary material Supplementary material at the source

Footnotes

Edited by: Praveen Kumar Maghelal, Rabdan Academy, United Arab Emirates

Reviewed by: Hare Kılıçaslan, Karadeniz Technical University, Türkiye

Sabeeh Lafta Farhan, Wasit University, Iraq

Footnotes

CT-VR, Culturally tuned virtual-reality (evaluation framework); the framework proposed in this paper; VR, Virtual reality; ULSp, Urban leftover space; HMD, Head-mounted display; CAVE, Cave automatic virtual environment (a projection-based immersive VR system); PRISMA, Preferred reporting items for systematic reviews and meta-analyses; PICOS, Population, intervention, comparison, outcomes, study design; MMAT, Mixed methods appraisal tool; ROBINS-I, Risk of bias in non-randomized studies—of interventions; RoB, Risk of bias; OSF, Open science framework; CI, Confidence interval; TPB, Theory of planned behavior; BehaveFIT, Behavioral framework for immersive technologies; IPQ, Igroup presence questionnaire; PAD, Pleasure–arousal–dominance (affect model); GUESS-18, Game user experience satisfaction scale (18-item short form); CSQ-VR, Cybersickness in virtual reality questionnaire; SSQ, Simulator sickness questionnaire; VRSQ, Virtual reality sickness questionnaire; UMUX-LITE, Usability metric for user experience (Lite version); SUS, System usability scale; AHP, Analytic hierarchy process; GIS, Geographic information system(s); MCDA, Multi-criteria decision analysis; CR, Consistency ratio (in the analytic hierarchy process); MSW, Municipal solid waste; GCC, Gulf cooperation council; NDS, National development strategy (Qatar); NDS-1 (2011–2016), NDS-2 (2017–2022).