Towards transformation-oriented planning: what can sustainable urban mobility planning (SUMP) learn from transition management (TM)?

ABSTRACT The European Commission’s concept of Sustainable Urban Mobility Planning (SUMP) aims to prepare transport planners for the challenge of fundamental transformations to achieve climate-neutral and sustainable cities. While the concept has been widely adopted by European cities over the last decade, it can be asked whether SUMP is able to trigger the required transformative change in mobility systems. This paper critically reflects on the SUMP concept by systematically comparing it with the theoretical governance framework of Transition Management (TM), which is explicitly designed to foster transformative change. Based on a literature review, we examine similarities and differences between these approaches regarding the planning dimensions of context, content and process. Drawing on this comparison, the paper demonstrates how SUMP could learn from TM in practice and research in four main ways: (i) utilising transition theory to better address transition features; (ii) using collaborative formats from TM while taking account of legitimacy concerns; (iii) incorporating backcasting approaches; and (iv) explicitly integrating experiments into the process cycle. The paper exemplifies how insights from transition research can stimulate the further development of procedures, methods and tools towards transformation-oriented planning.


Introduction
To move towards sustainable and climate-neutral mobility systems as envisioned by the European Green Deal (European Commission, 2019), the European Commission stresses that "we must shift the existing paradigm of incremental change to fundamental transformation".(European Commission, 2020a, p. 2).For the Commission, urban transport planning plays a vital role in achieving sustainable mobility (European Commission, 2011, 2020a).
After identifying major sustainability challenges in urban mobility in the early 2000s (partly rooted in traditional planning practices), the European Commission published its Action Plan on Urban Mobility.This plan recommends supporting the development of so-called Sustainable Urban Mobility Plans (European Commission, 2009;May, 2015).Subsequently, major efforts have been launched to change urban transport planning practice by specifying and disseminating the Sustainable Urban Mobility Planning (SUMP) concept throughout Europe (Werland, 2020).Initial guidelines for "developing and implementing a sustainable urban mobility plan" (Wefering et al., 2014) were published as part of the urban mobility package (European Commission, 2013).Along with complementary resources (Eltis, 2021) these guidelines provide guidance for planners and were updated in 2019 (Rupprecht Consult, 2019).At the heart the of the concept is the so-called SUMP-cycle, which encompasses four planning phases: (i) preparation and analysis (e.g.analysing stakeholders and challenges); (ii) strategy development (e.g.defining future mobility scenarios, a vision and targets); (iii) measure planning (e.g.identifying policy-packages); and (iv) implementation and monitoring (Rupprecht Consult, 2019).Today, SUMP has become "Europe's de facto urban transport planning concept" (Rupprecht Consult, 2019, p. 9).
Yet the question arises whether SUMP is sufficient to support the fundamental transformations (here used synonymously with "transitions") that the European Commission identifies as necessary to achieve sustainability.Urban mobility transitions are highly complex: they not only involve changes in vehicles, infrastructures, mobility options and travel behaviour but also require new policies, regulations and approaches to planning and governance as well as changes to socio-cultural norms and the meaning of mobility (e.g.desirable images of urban mobility, status symbols) (Canitez, 2019;Geels, 2018;Schwanen, 2015).Moreover, urban mobility transitions are interconnected with changes in other sectors such as land use or public health (Banister, 2008;Koszowski et al., 2019).Transitions evolve over long time frames of several decades (CREATE, 2018a) and are impacted by unpredictable events and trends (e.g.shifting societal preferences, economic developments, global crises) (Lyons & Davidson, 2016;Marchau et al., 2010) as well as the local context (Buehler et al., 2017;Schippl & Truffer, 2020;Schwanen, 2015).Since transitions are influenced by multiple actors with diverse roles, responsibilities, interests and levels of authority, they are inevitably conflictual, contested and normative (e.g. the selection of objectives and suitable measures) (Avelino, 2017;Hodson & Marvin, 2010;Marletto, 2014).Tensions between such features of sustainability transitions and established planning have provoked a lively debate around the question: Does planning act to advance or hinder transitions?(e.g.Carroli, 2018;Malekpour et al., 2015;McCormick et al., 2013;Wolfram, 2018).
The purpose of this paper is to shed light on the relation between SUMP as a contemporary transport planning approach and the demanded urban mobility transitions.Transition Management (TM), which was explicitly developed as a governance concept to support sustainability transitions (Frantzeskaki, Bach, et al., 2018;Loorbach, 2010), serves as a critical lens to reflect on SUMP.TM processes aim to foster transitions by addressing transition features outlined above and by supporting potentially transformative innovations (Loorbach et al., 2021).Like SUMP, TM builds on a cycle encompassing four activities: (i) strategic activities to gain orientation (setting up the process, system analysis, long-term visioning); (ii) tactical activities to set a mid-term agenda for change (identifying actions and responsibilities to contribute to long-term objectives); (iii) operational activities including so-called transition experiments; and (iv) reflective activities that serve to constantly question and adapt the other activities (monitoring and evaluation).Wolfram (2018) suggests that planning can learn from TM to enhance its concepts, procedures and tools to accelerate transitions.Recent publications have confirmed the value of examining the relations between TM and procedures of governance and planning (e.g.Chaffin et al., 2016;Malekpour et al., 2020;Nwanekezie et al., 2021;Raynor et al., 2017;Wolfram, 2018).In particular, various studies have identified relations between TM and established mobility planning or SUMP (Jhagroe & Loorbach, 2018;Lindenau & Böhler-Baedeker, 2014;May, 2015;Smeds & Jones, 2020).Until now, however, there has been no systematic attempt to compare the concepts of TM and SUMP.Aiming to close this gap and contribute to discussions on how transport planning can benefit from sustainability transition studies (e.g.Bakker et al., 2014;Naess & Vogel, 2012;Switzer et al., 2013;Torrens et al., 2021), we formulated the following research questions: (1) What are the conceptual similarities and differences between TM and SUMP in terms of fostering sustainability transitions?(2) To what extent and how can conceptual aspects of TM be integrated into SUMP to strengthen its transformation-orientation?
After this introduction, we outline our methodological approach to answering these questions.We then present the results of comparing both conceptsstructured along the dimensions context, content and process (Section 3) and illustrate options for applying aspects of TM to SUMP (Section 4).Finally, we summarise our findings, draw some conclusions on ways of moving towards transformation-oriented planning and reflect on limitations of our methodological approach.

Methodological approach
To identify ways of strengthening the transformative orientation of SUMP, the concepts of TM and SUMP were systematically compared by means of a literature review.
To gather relevant literature, we searched scientific databases (i.e.Scopus, Google Scholar) using the keywords "Transition Management", "Transition Governance", "'Sustainable Urban Mobility Planning' OR SUMP" and search strings combining these keywords.Furthermore, the practice-oriented Eltis database, 1 which contains additional knowledge for SUMP practitioners (e.g.briefings, topic guides), was screened for relevant resources giving concrete details of SUMP.Further resources were identified by reading the gathered literature.
Two rationales were followed in selecting and reviewing relevant literature: First, key publications were pinpointed and reviewed to identify the core features of the two concepts.These key publications should describe the basic ideas behind TM or SUMP as comprehensively as possible and be considered relevant in science or practice according to their diffusion.Regarding TM, key publications include Loorbach's foundational work (2007,2010), various scientific conceptualizations of urban TM (e.g.Frantzeskaki, Hölscher, Bach, & Avelino, 2018;Loorbach et al., 2021;Nevens et al., 2013) and the practice-oriented guidelines of Roorda et al. (2014).Regarding SUMP as a practical concept, the second edition of the guidelines (Rupprecht Consult, 2019) sums up the concept and integrates insights gained from previous SUMP applications and research projects.Second, we identified further publications which (critically) reflect on the concepts in general or in relation to specific aspects such as legitimacy (e.g.Kenis et al., 2016), foresight methods (e.g.Smeds & Jones, 2020) or concrete tools (e.g.Hebinck et al., 2022).These were included in the review to enable a deeper understanding of the concepts.
To systematically compare SUMP with TM, the literature was reviewed by applying the planning dimensions framework developed by Wiechmann (2008Wiechmann ( , 2018)).This framework distinguishes three strongly interlinked dimensions: context (why to plan?), content (what to plan?) and process (how to plan?) (Wiechmann, 2008(Wiechmann, , 2018)).Context describes relevant societal challenges (here: sustainable urban mobility) as well as the governance structures, organisations and legitimation of planning which influence the scope of action for planning.Content relates to the issues and problems addressed, the lenses through which they are perceived and the mechanisms used to influence developments.Process covers the procedures and instruments of decision-making, which involves a wide range of actors (Wiechmann, 2008(Wiechmann, , 2018)).
The results of the comparison were explored at two structured discussion workshops within the authors team, which were set up to identify opportunities for utilising TM aspects in practical SUMP guidance or research on SUMP.The discussions focused on the degree to which these aspects of TM are compatible with the context of SUMP, whether they could strengthen the transformative orientation of SUMP and on concrete proposals for SUMP practice and research.

Context
3.1.1Origin and background of the approaches SUMP emerged from a European Commission initiative aimed at improving urban transport planning practice in the face of persistent sustainability challenges.The concept draws on experiences of local transport planning practice, existing national guidance and research on urban transport planning.A wide-ranging dialogue between stakeholders and planning experts from across the EU was established to specify the details of the concept (May, 2015;Rupprecht Consult, 2019).The first edition of the central guidelines was published in 2014 (Wefering et al., 2014), with the second edition following in 2019 (Rupprecht Consult, 2019).Ongoing research projects such as CIVITAS SUMPs-UP, CIVITAS SUMP-PLUS and CIVITAS SUITS contribute to SUMP's development.While grounded in established transport planning practice, the explicit intention of SUMP is to move away from traditional (car-oriented) planning approaches and paradigms (see the table in Rupprecht Consult, 2019, p. 10).
In contrast, TM emerged around the early 2000s in the academic field of sustainability transition studies (Köhler et al., 2019;Markard et al., 2012).As a theoretical concept, TM is explicitly designed to address various aspects of transitions (Loorbach, 2007).At the same time, it has frequently been applied to participatory processes and has grown and developed from these applications (for an overview Frantzeskaki, Hölscher, Wittmayer, et al., 2018).

Governance structures
SUMP is designed to be incorporated into the work of transport departments of city administrations.As established actors, these departments are expected to initiate and facilitate planning processes.They apply the SUMP concept to fulfil their mandatory tasks of managing and developing the local mobility system.SUMP is thus implemented within established governance structures where two factors hinder its transformative potential: First, local planning institutions have a legacy of (traditional) planning procedures and techniques and adhere to existing norms and (sectoral) distributions of responsibilities that have sometimes remained unchanged for decades (Wolfram, 2018).These experiences serve as an orientation for current activities, even if they are not suited to current transition challenges.Paradigmatic change must therefore overcome this inherent institutional inertia (Carroli, 2018).Second, administrations favour systematic and sequential procedures, standardised methods, measurable outputs and foreseeable futures to justify decisions (Carroli, 2018;Peris & Bosch, 2020).In contrast, transitions can be described as uncertain and context-dependent, i.e. they do not follow a standard script.Clearly, flexibility and adaptability are required to achieve the desired ends.
Unlike SUMP, TM was not developed as a tool for established planning authorities.In fact, it is designed to remain independent of existing planning institutions and established governance structures (Wittmayer, 2016;Wolfram, 2018).Instead, TM complements existing governance activities while establishing its own governance structures (also framed as "governance niches") (Roorda et al., 2014;Wolfram, 2018).Therefore, TM should be initiated by actors who aim for transformative change and explicitly adhere to objectives such as a mobility transition.These actors may be associated with public administrations but can also be entirely independent of them, e.g.grass-root initiatives (Roorda et al., 2014).TM processes should be facilitated, i.e. implemented and moderated, by independent actors such as local research institutions (Loorbach, 2010).Under this approach, TM can provoke and ask ambitious questions, including the roles and responsibilities of actors (Hölscher, 2018;Wolfram, 2018).However, very practical steps must be taken to achieve the change envisioned.In particular, the adaptation of mobility systems including major infrastructures requires time, staff and financial resources as well as the support of local administrations and political leaders.TM must constantly strive to retain independence while meeting these practical needs (Ehnert, Frantzeskaki, et al., 2018;Ehnert, Kern, et al., 2018;Loorbach et al., 2017).

Legitimation
To gain legitimacy, SUMP involves a representative array of societal actors as well as seeking the approval of decisions by democratic institutions such as the city council.In this way, SUMP aims to secure societal and political acceptance by seeking consensus (Rupprecht Consult, 2019;Wefering et al., 2014).City administrations and elected politicians are accountable for outcomes of SUMP processes.In doing so, SUMP tries to address the requirements of liberal democracy.
TM is less concerned with acceptance and representation.Instead, the key source of legitimacy here is scientific knowledge of the need for fundamental societal transitions to meet sustainability targets (Voß et al., 2009;Wolfram, 2018).TM has been strongly criticised for this seemingly weak approach to legitimacy in liberal democracy (e.g.Hendriks, 2009;Kenis et al., 2016;Smith & Stirling, 2008).According to a recent review by de Geus et al. (2022), two main criticisms have been expressed (for a further discussion see also the review by Corais et al., 2022).The first concerns TM's approach to participation and the uncritical selection of actors.Facilitators of TM processes have to decide who will participate based on assumptions regarding actors' knowledge, motivation, influence and availability, etc. (Geus et al., 2022).As long as these criteria are not revealed or critically discussed (Hendriks, 2009), TM risks assigning decision-making on future strategies to a non-democratically selected "elite" of actors (Geus et al., 2022).The second main criticism revolves around the risk of depoliticising sustainability issues, i.e. by ignoring the fundamental ideological conflicts underlying strategic decisions (e.g.market-oriented vs. regulatory measures) or the inevitable power imbalances between actors.Some scholars insist that TM hides these conflicts by highlighting the achieved consensus on an abstract long-term vision of sustainability (Geus et al., 2022;Kenis et al., 2016), whereby powerful actors may exploit the proclaimed consensus to promote their own agenda (Kenis et al., 2016).Moreover, since TM builds on the voluntary commitment of actors, it may fail to hold actors responsible and accountable for decisions made within TM processes (Hendriks, 2009).
Table 1 summarises the different structural contexts for applying TM or SUMP.The features of TM regarding its urge to remain independent and legitimacy questions outlined above support Wolfram's (2018) argument that TM cannot simply replace existing governance activities as applied by established planning authorities.Nevertheless, TM can be used as a critical lens to reflect on planning approaches such as SUMP while contextual differences must be carefully considered when drawing practical conclusions for SUMP (focus of this paper).It can also function as a complementary governance activity to existing SUMP procedures (Wolfram, 2018).
Conceptually, TM keeps the definition of sustainability completely open: it should be negotiated between local actors acknowledging their values and beliefs (Loorbach,  2010).This openness has been criticised for potentially emptying the term "sustainability" of meaning, i.e. it becomes completely negotiable and free of any principles (e.g.climate neutrality) (Rauschmayer et al., 2015).While this argument is aligned with the criticism of TM that it depoliticises sustainability issues, paradoxically, such openness can create space to ask political questions regarding desirable futures and to discuss underlying assumptions, values and beliefs, and thus determine what sustainable actually means in a local context (Kenis et al., 2016;Schäpke et al., 2017).
In contrast, SUMP offers a more tangible guiding definition of "a sustainable transport system" by referring to basic criteria such as providing accessibility, creating a balance between "economic viability, social equity, health and environmental quality" and "making effective use of urban space and of existing transport infrastructure and services" (Rupprecht Consult, 2019, p. 11).The prioritisation of these aspects is negotiated at the local level.

Scope of mobility systems and theory of change
Both approaches acknowledge the complexity of mobility systems, which necessarily encompass a variety of societal and technological elements (e.g.infrastructure, mobility options including all modes, policies and regulations, mobility patterns, cultural meanings, governance and planning).These systems are interdependent of other sectors such as land use, health or business development, are embedded in multi-level governance structures (municipal, regional, national, supranational) and involve a variety of actors with diverse values, interests, objectives and power (Loorbach, 2010;Malekpour et al., 2020;Rupprecht Consult, 2019).TM and SUMP differ in terms of how concrete system boundaries are defined and which aspects are highlighted.
Taking a transition challenge as its starting point, TM is rather flexible in defining and delineating the system under consideration (Malekpour et al., 2020;Roorda et al., 2014).Conceptual system frameworks from the field of socio-technical transition studies are used to understand the complex systems and interrelations between the various elements and actors (e.g.Marletto, 2014;Schippl & Truffer, 2020;Switzer et al., 2013).Theories used in TM are highly sensitive to potentially transformative innovations and actors associated with them (Avelino, 2017;Roorda et al., 2014).
The SUMP guidelines specify the scope of the mobility system more precisely.For instance, plans should integrate all modes and include "infrastructure, technical, regulatory, promotional and financial measures" (Rupprecht Consult, 2019, p. 12) as well as develop capacities for improved planning and implementation (Kalakou et al., 2021).The guidelines explicitly suggest planning for the spatial scope of an entire "functional urban area" (Rupprecht Consult, 2019).

Theory of change
TM and SUMP treat transitions in urban mobility as a question of the dynamic interactions between the various elements of the mobility system under consideration.
Again, TM draws on concepts from sustainability transitions literature (Frantzeskaki, Bach, et al., 2018;Loorbach et al., 2017) that define characteristics of transitions such as co-evolution, deep uncertainty and path dependence.These concepts are used to analyse, understand and anticipate processes of change (see e.g.Geels, 2012Geels, , 2018)).For instance, the "X-curve" model of transitions was developed within TM as an actionable tool for collaboration (Loorbach et al., 2021).The X-curve conceptually and visually illustrates how transitions unfold as two opposing and equally important processes, namely: (a) the build-up of new solutions and structures; and (b) the breakdown of established (old) solutions and structures.Phase patterns of various transition phases are defined for both processes to facilitate an understanding of the current state of processes of change and to identify actions that support or counteract these (for an insightful review on the X-curve and an application for a mobility system, see Hebinck et al., 2022).
While SUMP is not grounded in an explicit theory of change, it is nonetheless inevitable that the broad repertoire of methods and heuristics it refers to is founded on assumptions about how change evolves and can be influenced (e.g. by particular forms of infrastructure, price mechanisms and combinations of push and pull measures; see following section).But these relations has been little investigated.

Mechanisms to influence developments
Both approaches assume that local actors can, to a certain extent, influence change towards sustainability.Here they highlight the need for two-pronged approaches, 2 namely to foster sustainable solutions and at the same time restrict those deemed unsustainable.In practice, that essentially translates to a mix of measures that restrict car use and promote alternatives such as walking, cycling or public transport (Kivimaa & Kern, 2016;Rupprecht Consult, 2019).Both TM and SUMP highlight the need for coordination and cooperation between actors at all levels of governance, from all sectors and from all modes of transport as the interdependencies between them determine the possibilities of change.The difference between the approaches lies in the radicalness of change envisioned, and the role of actors in the processes.
TM strongly focuses on introducing radical innovations that substantially diverge from the status quo and on triggering transformative change.Here the notion of what constitutes a radical innovation is highly contextual (Geus et al., 2022): whereas introducing a network of protected cycling tracks will be radical in a city with no previous cycling infrastructure, this will be regarded as conventional in bicycle-friendly cities such as Copenhagen or Amsterdam (Bertolini, 2020;Schwanen, 2015).
Moreover, TM assumes that powerful actors and established actor constellations tend to maintain the status quo.Conversely, the aspired radical innovations require changes in the roles of actors, their understanding of the problem and in power constellations and networks.Therefore, TM focuses on those actors willing to support transformative change (so-called "change agents").These can be, for instance, individuals from municipal transport departments, private (car sharing) companies or citizen initiatives for liveable streets.TM aims to enhance the actors' knowledge, resources and networks by involving them in collaborative processes (see subsection 3.3.2for more details).In this way, actors should come to understand how change may unfold, question their own assumptions, beliefs and roles ("social learning"), connect to other actors sharing the same visions, create coalitions to enhance their collective power to influence change ("network building") and strengthen their intrinsic motivation and abilities ("empowerment") (Avelino, 2009;Nevens et al., 2013;Schäpke et al., 2017).Since the envisioned change depends on the actions of the actors supported by TM, these must be carefully selected to ensure democratic legitimation (see subsection 3.1.3).Under this approach, TM assumes that the voluntary coordination of these actors will be effective in fostering change.
In contrast to TM, the focus of SUMP is on measures for sustainable mobility that have to be planned by the public administration and then implemented with partners (e.g.public transport companies, civil society networks).While SUMP highlights acceptance of measures among citizens, stakeholders and political leaders to legitimate actions, less emphasis is placed on radical change and the need to alter power constellations of actors.Moreover, the need to establish broad consensus on strategies and measures may undermine or hinder radical changes since these are often a source of conflict.
To sum up, we find differences in the content of the approaches regarding the use of theory, the openness of definitions and the mechanisms to influence developments (summarised in Table 2).While TM strongly draws on concepts and assumptions of transition theory, it only vaguely defines sustainability and system boundaries.To foster change, TM relies on the voluntary commitment of actors willing to support change and thus engages with this target group.In contrast, SUMP offers more concrete and pragmatic definitions of sustainable mobility systems while lacking an explicit theory of change.To implement change, SUMP mainly concentrates on those instruments available to public administrations.These findings reflect the particular contextual requirements of TM and SUMP regarding legitimation and governance structures.

Process 3.3.1 Process structure
Structurally similar, the processes in TM and SUMP are based on a cycle that encompasses participatory, strategic, tactical, operational and reflective governance activities (see the process cycles in Loorbach, 2010;Roorda et al., 2014;Rupprecht Consult, 2019).The processes are modular; steps can be processed iteratively and should be arranged in a context-sensitive way (Raynor et al., 2017;Rupprecht Consult, 2019).
In order to identify and utilise "windows of opportunities" (Harlow et al., 2018;Loorbach, 2010), TM explicitly gives users greater freedom.TM processes evolve over time by flexibly adapting to changing conditions guided by the locally-defined transition challenge (e.g.climate neutral mobility).
In contrast, SUMP more strongly structures the process to meet the requirements of administrations and representative democracy.For instance, political representatives should approve planning decisions at certain predefined milestones.In combination with systematic methods and tools, SUMP aims to ensure the legitimation of decisions, but may undermine flexibility.

Involving actors
TM and SUMP advocate the close involvement of societal actors throughout the entire process to enhance the quality of outputs (e.g.planning documents, visions, measures) and outcomes (e.g.changes in decisions regarding sustainable mobility).Both approaches acknowledge that power imbalances in participatory processes mean that established and powerful actors could potentially exercise their power to shape or prevent change (Rupprecht Consult, 2019;Voß et al., 2009).Although these assumptions are similar, they lead to rather different approaches and ways of involving actors.
As mentioned before, TM uses participation to enhance the capacities of motivated actors to influence change by involving them in a collaborative format, the so-called "transition arena".The arena acts as a protected environment whereas free as possible from external constraintsa network of actors can collaboratively seek sustainable solutions.In doing so, they come to understand local mobility systems, pinpoint opportunities for or barriers to change, envision alternative images of urban mobility, develop ideas for transformative actions, build networks and actively undertake experiments (Frantzeskaki, Bach, et al., 2018;Nevens et al., 2013;Roorda et al., 2014).
In contrast, SUMP prioritises the need to secure legitimacy by involving actors representing all societal groups.This includes both minority groups and powerful, established actors.To "[s]trive for a broad coalition that supports your SUMP and feels ownership" (Rupprecht Consult, 2019, p. 40), SUMP makes use of open citizen participation formats and formats that involve selected actors.

Strategic activity: gaining system insights
To identify current problems in sustainability and opportunities for change, a key component of both processes is to analyse the entire mobility system, including the relevant actor constellations.However, the approaches differ in their focus and in the ways that users are guided.
TM aims to identify existing dynamics of change that support or hinder sustainability transitions (Loorbach, 2010).To identify such dynamics, an evolutionary perspective is applied to take account of historical development pathways and identify path dependencies.The analysis is guided by theories of transitions (e.g.X-curve) while step-by-step methodological guidance is rarely given (Malekpour et al., 2020).
SUMP offers a multitude of concrete methods to identify current sustainability problems, risks and opportunities.For instance, the Civitas Tool inventory suggests methods for manifold tasks, e.g.stakeholder analysis, accessibility assessments and map-based surveys (CIVITAS, 2021).

Strategic activity: visioning and foresight
To gain long-term orientation and develop a strategy, both approaches make use of longterm visions and scenarios of the system to generate knowledge of "desirable" and "possible" futures.Here, the procedural logics, foresight methodologies and rationales differ.
TM first develops a vision of a desirable future state of urban mobility as well as the meaning of sustainability in a certain local context.This vision, which should diverge radically from the status quo (Loorbach, 2010;Roorda et al., 2014), must be sustainable, motivational and express a shared ambition of the participants (criteria according to Wiek & Iwaniec, 2014).Subsequently, transition pathways are developed to bridge the gap between the status quo and the vision using collaborative backcasting approaches (Hyysalo et al., 2019;Roorda et al., 2014).In essence, TM asks: What do we need to change to achieve the vision?(Vergragt & Quist, 2011).This step aims to move away from accustomed ways of thinking to discover potential innovations and transition barriers.The end result is to create motivational narratives of pathways towards sustainable urban mobility futures that are used to engage with interested actors (Malekpour et al., 2020;Roorda et al., 2014).
In SUMP, the initial step is to develop scenarios as a set of alternative futures deemed "plausible" but ambitious.Developed scenarios should "capture the scope of uncertainty that comes with 'looking into the future' in order to have a better factual basis for strategic decisions" (Rupprecht Consult, 2019, p. 79).In this way, SUMP asks: Which longterm strategies may be effective, feasible and realistic?(Rupprecht Consult, 2019).Transport models support the development of scenarios by calculating the probable effects of different strategies on mobility behaviour.Visions are developed within the boundaries of future scenarios to ensure their feasibility.The vision should be shared and accepted by a broad range of actors.At the end of this step, visions are translated into tangible objectives and indicators guided by tools such as indicator sets (e.g.European Commission, 2020b) in order to track success.

Tactical activity: agreeing on shortand mid-term actions
To distil these ideas on long-term futures into concrete measures, TM and SUMP outline measures and actions which should be realised in the short-term (3-5 years) and mid-term (5-15 years).To ensure broad visibility of the process results, summarising documents are prepared to give an overview of all actions and responsibilities as well as underlying visions and pathways ("transition agenda" in TM; "Sustainable Urban Mobility Plan" in SUMP).The rationales behind this step vary.
Actions in TM processes are entirely reliant on voluntary commitment (Roorda et al., 2014;Wolfram, 2018).TM stresses that the agenda must be communicated in a motivational way to actors (beyond the transition arena), who should then engage with the visions, pathways and actions by taking over responsibilities or supporting the ideas (Roorda et al., 2014).
In SUMP, the focus is rather on municipal actions (e.g.regulations, infrastructure, coordination, information) that have to be accepted by citizens, stakeholders and political decision-makers.Accordingly, emphasis is placed on the justification of planning decisions, a step which mostly relies on systematic procedures and tools for identifying, packaging and appraising (e.g.multi-criteria assessment, cost-benefit analysis, participatory assessments) measures.For this purpose, SUMP offers a variety of tools (e.g.May, 2016;University of Leeds, 2016).

Operational activities: experimenting and implementing
Actions identified in the transition agenda or action plan are realised at the operational level.Here, there is a fundamental difference between the approaches: In TM, operational activities are framed as transition experiments which test novel solutions for sustainable urban mobility (innovations).In doing so, TM aims to cope with unpredictable outcomes of radical changes through learning by doing.Transition experiments are designed to differ from the status quo, address transition challenges, be feasible in the short-run, mobilise a broader group of actors and strategically help to achieve the long-term vision (Bertolini, 2020;Roorda et al., 2014).A vital step is to institutionalise the tested innovations: either the innovations fit into the existing regulatory and organisational frame without losing their transformative potential or the frames themselves must be adapted to the innovation (Ehnert, Frantzeskaki, et al., 2018;Ehnert, Kern, et al., 2018;Hölscher, 2020).
In contrast, SUMP concentrates on the successful implementation of measures that are well-appraised and widely accepted.These measures can be conventional or may be radical in some aspect.Furthermore, SUMP provides guidance on how plans can be translated into administrative processes and legal frameworks (e.g.CIVITAS SUMPs-UP, 2021).

Reflective activities: monitoring and evaluation
As both TM and SUMP aim to learn from experience, they include monitoring and evaluation procedures for three aspects, namely: the development of the mobility system, the impact of operational activities and the TM/SUMP process itself.
TM's process cycle emphasises the need for constant reflection, learning and adaptation of assumptions, norms, values and roles (Loorbach, 2010;Roorda et al., 2014).Yet TM processes address rather intangible learning outcomes (e.g.understanding of transitions, changing discourses, network building), which are difficult to operationalise and consequently challenging to evaluate (Peris & Bosch, 2020;Schäpke et al., 2017).
In SUMP, on the other hand, concentrates on evaluating and monitoring tangible developments.These are assessed using sets of indicators that reflect the vision.Guidance is given on suitable methods and tools for monitoring and evaluation (e.g. on the planning process itself: Rupprecht Consult, 2021).
Generally speaking (see Table 3), the clearer structure of SUMP processes and the stepby-step guidance on methods as well as the focus on tangible outcomes articulates a rather engineering-oriented perspective of SUMP.That aligns with SUMP's governance context.TM processes, on the other hand, are shaped by transition theory and the respective transition challenge, which together serve to create a highly communicative, collaborative and action-oriented but less tangible process.

Integrating aspects of TM into SUMP
This section identifies to what extent and how conceptual aspects of TM can be utilised in SUMP to strengthen its transformation-orientation.This relates to improving practical guidance on SUMP contents and processes as well as outlining directions for further research activities in the context of SUMP.Before discussing these in detail, it is important to first acknowledge the similarities of both approaches.While SUMP evolved from rather technocratic traditional approaches to transport planning, it follows TM in significantly departing from these in several key ways, namely by: . setting sustainability as the explicit normative objective; . treating change of urban mobility as a complex and context-specific challenge; . stressing the need to support sustainable mobility solutions and to restrict unsustainable car use; . providing (at least some) modular options to design a planning process that meets the contextual requirements; .integrating participatory elements; . using long-term visions for strategic guidance and aligning short-term actions to them; . integrating monitoring and evaluation procedures into the process.
However, there are clear differences between TM and SUMP.While the former aligns itself more closely with transition theory and establishes transformative long-term sustainability visions, SUMP is more focused on creating plans for urban mobility that are ambitious but also deemed feasible and realistic.TM is strongly attached to the ideal of communication and collaboration between participants.In doing so, it places transitions at the centre of discussions and aims at mutual learning.Although SUMP incorporates communicative elements, it can still be described as engineering-oriented in order to satisfy the need to justify decisions.TM focuses on actors willing to support change, reasoning these efforts with the need for transition.SUMP aims at legitimation.These differences reflect the contexts in which the approaches were developed and underline that TM cannot simply replace SUMP as an approach to transport planning in city administrations; this would require either a fundamental shift in governance institutions or the further elaboration of TM to address the administrative and democratic requirements (Wolfram, 2018).Yet it is doubtful if the former is realistic or even desirable if we wish to retain the norms of liberal democracies.Equally, it can be questioned whether adapting TM to the existing governance institutions would damage TM's abilities to address transition features.Considering these similarities, differences and relations between TM and SUMP, we have identified four aspects of TM that could strengthen the transformative orientation of SUMP in practice and research and discuss them in the following four subsections.
4.1 Sharpening the repertoire of SUMP tools by understanding complex transitions and borrowing from TM Guided by transition theories, TM highlights the need to understand transitions.In contrast, SUMP does not have such a theoretical fundament and is more "hands on" by providing a huge body of guidance and tools for specific tasks.While extremely useful, this repertoire has evolved over time without explicit consideration of the features of transitions.As this neglect may undermine SUMP's ability to support transitions, SUMP can benefit from transition theories to sharpen existing tools and integrate additional tools to better address the specific features of transitions.
For instance, established transport simulation models calibrated to the current state of the system can poorly capture the impacts of future visions that diverge radically from the status quo (Avelino, 2009).A strong reliance on such modelling results can cause planners to neglect such futures since they are outside the scope of the modelling results.For this reason, transportation scholars have criticised the use of transport demand models in long-term planning (Lyons, 2021;te Brömmelstroet & Bertolini, 2011;Timms, 2008).By using concepts from transition theory research can help to better understand the strength and limitations of transport simulation models in the context of mobility transitions and to develop models able to better capture transformative change.In other domains, it has proven useful to use transition theory as an analytical lens to examine particular modelling and assessment techniques.The insights gained provide information about these approaches' ability to capture transitions (see e.g.Köhler et al., 2018;Mercure et al., 2021).In doing so, better models and guidance on using them can be developed.
In practice, ideas and tools from TM can be used to better understand the transition dynamics of urban mobility systems, especially developments that hold opportunities or barriers for change.Understanding complex transition processes can be challenging, specifically in participatory formats (Nagorny-Koring & Nochta, 2018).The X-curve from TM acts as a simple but actionable and communicative tool for this purpose (Hebinck et al., 2022;Loorbach et al., 2021).It helps participants learn about transition challenges while reflecting on their own assumptions, roles and influence to foster change (Hebinck et al., 2022).This tool could be tested for system analysis in SUMP using collaborative formats.It can be adapted to the field of urban mobility by learning from existing tools, such as the system assessment tool of CREATE which proposes system dimensions for the analysis, such as evolutions in car use, visions for the city, policies, etc. (CREATE, 2018b).The use should be evaluated, e.g.regarding the impact on actors' knowledge of urban mobility transitions.

Using collaborative formats and addressing legitimacy questions
TM assumes that existing and dominant assumptions, values and beliefs about mobility systems (e.g.no economic development with less transport, automobility as a symbol for freedom and wealth; see Black, 2001;Essebo, 2013) need to be questioned in order to realise desired sustainability transitions.To this end, TM suggests that actors should reframe their assumptions and beliefs by collaboratively questioning what is required to achieve urban mobility transitions.The so-called "transition arena" is the format designed to foster this process by involving selected actors.
This transition arena could be adapted as a format for collaboration in SUMP processes.Smeds and Jones (2020) suggest using this format to establish a small network of actors (e.g. from public administrations, civil society or scientific institutions) who are willing to support the transition.In the arena, these actors gain ownership of developed transition pathways, which they revise and debate over time and constantly take over responsibilities for the implementation (Smeds & Jones, 2020).
However, as indicated before, the tensions between such participatory formats to foster transitions and questions of legitimacy in liberal democracies deserve further scrutiny.While there is a growing debate about these issues in TM (see 3.1.3),Marsden and Reardon (2017) suggest that transport planning suffers from a general lack of research into legitimacy, power and contestability.SUMP procedures should be studied from this perspective and discussions around this topic in TM could act as a starting point to do so.For instance, de Geus et al. (2022) present a framework for legitimacy in TM processes, which, by incorporating norms of liberal democracies and normative dimensions of transitions, offers insights into tensions between these aspects and suggests ways of improving governance processes.This framework could be refined for application to urban mobility.It could be used to evaluate the legitimacy of SUMP applications in various cities acknowledging different process designs (e.g.choice of actors involved, types of participatory formats).Guidance on how to balance legitimacy with the needs of transitions can be developed for further SUMP applications.

Backcasting transition pathways
Collaborative backcasting is used in TM to collectively question the status quo and to develop future visions that diverge from established pathways (Vergragt & Quist, 2011).For a more transformation-oriented approach, SUMP should strive to move away from forecasting-based scenario planning with a stronger present-orientation (Naess & Vogel, 2012;Smeds & Jones, 2020).Hence, it is recommended that SUMP uses backcasting for strategy development.For instance, Smeds and Jones (2020) suggest a practice-oriented approach to develop a so-called "transition pathway" in SUMP processes (similar approaches are proposed by e.g.CREATE, 2018b;Lyons & Davidson, 2016).Briefly, this approach can be broken down into five stages: First, a long-term vision of the desired mobility system embedded in a broader city vision is developed.Second, backcasting is used to identify a policy mix sufficient to achieve this vision.Third, explorative scenarios are developed to map uncertain external developments and to stress-test the policy mixes.Fourth, enabling measures are identified regarding the institutional capacity and financial resources.Finally, the transition pathway is presented as a motivational and communicative narrative (as in TM).
Furthermore, as Sustar et al. (2020) suggest research should create systematic and communicative methods (e.g. based on the backcasting idea) for deliberative envisioning and speculation of radically different future mobility systems.Such methods can be developed by drawing on transport and the transition literature (e.g.Hyysalo et al., 2019;Soria-Lara & Banister, 2017;Varho & Tapio, 2013).
In addition, scholars could devise and assess radical mobility visions (e.g.images of cycling cities 3 ) (Torrens et al., 2021) to provide inputs for the deliberation of desirable and possible futures in SUMP processes.

Integrating transition experiments into the SUMP cycle
In contrast to SUMP, TM conducts experiments to actively deal with uncertainty and to expand the range of future options considered possible.Such experimentation is not new to transport literature and has been shown as vital to realise a shift away from car-centred policies (CREATE, 2018a).However, Bertolini points out the challenge of "finding ways to not just tolerate, but rather proactively shape institutional and physical space for experimentation, and for learning from it". (Bertolini, 2020, p. 750).
Such spaces could be developed by integrating experiments into the SUMP cycle along with strategy development, measure planning and implementation.Insights from experiments (e.g. on barriers for solutions or on the impact of experiments) could feed back into planning to adapt regulatory, institutional, funding and operational structures and processes (e.g.administrative procedures, regulatory norms, responsible actors) or to refine and improve the tested solution (Bos & Brown, 2012;Hölscher, 2020).Successfully tested solutions may lead to measures that foster a broader implementation.Smeds and Jones (2020) discuss the integration of experimentation into the implementation stage of SUMP.Clearly, political aspects of experiments and their legitimacy (Savini & Bertolini, 2019) must be further investigated to provide further practice-oriented guidance for SUMP processes.

Conclusions
This paper examined TM and SUMP as two approaches aimed at fostering change towards sustainable urban mobility.A first systematic comparison outlined similarities and differences regarding the dimensions context, content and process.Based on the results, we identified how SUMP could become more transformation-oriented by incorporating aspects of TM.In doing so, we contribute to discussions on the relations between planning and transitions in both fields (Stead, 2016;Torrens et al., 2021) and identify trajectories for SUMP and research in this context.Furthermore, the developed analytical framework may prove useful for the evaluation and design of TM and SUMP processes.
SUMP represents a major step forward from traditional approaches to transport planning.However, we see room for improvement towards a more transformation-oriented planning.To move in this direction, SUMP can borrow from TM in the following four ways: First, transition theory and its heuristics, such as the X-curve, could be used as a conceptual layer to question and improve the procedures, methods and tools of SUMP.Second, SUMP could incorporate collaborative TM approaches, such as the transition arena, to strengthen social learning (i.e. by questioning and reframing assumptions, values and beliefs) and network-building of relevant actors as mechanisms to foster change.Yet, further research is needed to investigate tensions between such participatory formats and questions of legitimacy and power.Third, more backcastingbased approaches could be developed and used to generate strategies in SUMP and, fourth, experimentation with more radical solutions should be integrated into the SUMP cycle.
In part, these aspects are hardly new to transport literature.For example, various papers cited above deal with backcasting or experimentation in urban mobility.Research could support a better integration of these approaches into SUMP by developing methods and tools tailored to the needs of SUMP practitioners (e.g.what an applicable step-by-step backcasting process looks like; how to design and evaluate mobility experiments).In doing so, transition features as well as practical and theoretical findings in TM literature (e.g.process designs and outcomes, barriers to applying certain tools and concepts, discussion on legitimacy) should be taken into account.Transdisciplinary research settings have proved useful in TM to gain practice-oriented knowledge and can be used for a better integration of transformative aspects in the context of SUMP as well.
To support the diffusion of such approaches in practice, future transport planners should be equipped with the required knowledge.Transport planning degrees could cover transition management and transition theory to improve the understanding of the challenges of transitions among practitioners.
At the same time, policy at EU and national level must reconfigure regulatory planning frameworks according to the requirements of a more transformation-oriented planning (see e.g.Mäntysalo et al., 2023 for an insightful discussion on scenario planning and legal requirements) as well as provide guidance and support to cities to improve their transformative capacities (Wolfram, 2016).
Our methodological approach enabled a well-structured and comprehensible comparison of the concepts of TM and SUMP.The literature review gave a good overview on both concepts and helped to capture their basic components.We were able to address a range of issues relevant for transformation-oriented planning.Nevertheless, there are several limitations to our approach.The results are dependent on our interpretations of the rather abstract descriptions of the concepts in the gathered literature.Broader discussion among researchers and practitioners of TM and SUMP could help refine the results and their scope of applicability.Certain aspects such as legitimacy, the use of experimentation or the format of the transition arena need to be discussed at greater depth than was possible here.In addition, our proposals are based on the contestable assumptions that SUMP could be substantially adapted towards transformationoriented planning within the existing governance context and that the incorporation of TM elements will help foster transitions.
Overall, our work illustrates that to move towards transformation-oriented planning is challenging and a constant act of balancing various requirements.Insights from transition literature and transport planning can cross-fertilise one another and contribute to a revision of planning approaches to better resonate with transitions features.

Table 1 .
Comparative overview of TM and SUMP contexts.

Table 2 .
Comparative overview of TM and SUMP contents.

Table 3 .
Comparative overview of TM and SUMP processes.