The claimant, an environmental protection association that operates throughout Germany and is recognised under section 3 of the Environmental Appeals Act (UmwRG, Umwelt-Rechtsbehelfsgesetz), requests the updating of the Clean Air Plan (Luftreinhalteplan) for the city of Reutlingen, as a third party summoned to attend the proceedings as a party whose rights may be affected (hereinafter summoned third party).

A Clean Air Plan has been in place for Reutlingen since 2005 which provides for numerous measures to reduce levels of particulate matter and nitrogen dioxide pollution; it has been amended a number of times. The annual average limit value for nitrogen dioxide (NO₂) of 40µg/m³ was exceeded at one of the measuring stations each year between 2009 and 2017. The fourth update of the Clean Air Plan followed an Administrative Court (Verwaltungsgericht) judgment. 

An expert report underlying that judgment forecast an NO₂ value of 41μg/m³ without software updates and 39μg/m³ with software updates (passenger car retrofitting) in 2019 and respective values of 37 and 36μg/m³ in 2020.

In March 2018, the claimant submitted an application for an amendment of the Clean Air Plan. It brought an action on 3 April 2018.

In the expert report of 12 March 2019 submitted in the proceedings by the defendant federal state of Baden-Württemberg 48μg/m³ was forecast for 2019 and 44μg/m³ for 2020.

By judgment of 18 March 2019, the Higher Administrative Court (Verwaltungsgerichtshof) ordered the defendant to update the Clean Air Plan for the city of Reutlingen, so that it will contain the necessary measures to comply - as quickly as possible - with the immission limit value for nitrogen dioxide of 40μg/m³, averaged over one calendar year in the Reutlingen urban area.

The appeals on points of law brought by the defendant and the summoned third party met with partial success.

21 B. The appeals on points of law are partially well-founded. In line with federal law, the Higher Administrative Court decided that the Clean Air Plan for the summoned third party is based on a defective forecast and the defendant is required to update it. However, the Higher Administrative Court's statements on the permissibility and design of a traffic ban for diesel vehicles do not take full account of the principle of proportionality.

22 1. a) The claimant, as a recognised environmental association, has standing. Pursuant to section 2 (1) first sentence no. 1 UmwRG, an association that is recognised under section 3 UmwRG may, without having to assert that its own rights have been infringed, appeal in accordance with the Code of Administrative Court Procedure (VwGO, Verwaltungsgerichtsordnung) against a decision made under section 1 (1) first sentence UmwRG, that is to say under no. 4, also against a decision on the approval of plans and programmes within the meaning of section 2 (7) of the Environmental Impact Assessment Act (UVPG, Gesetz über die Umweltverträglichkeitsprüfung) for which there may be an obligation to carry out a strategic environmental assessment (SEA) under the Environmental Impact Assessment Act, if it claims that the decision or omission thereof infringes legal provisions that could be of importance for the decision. The Act requires legal remedies to have a suitable subject; the mere possibility that such subject existed is not sufficient (see Federal Administrative Court (BVerwG, Bundesverwaltungsgericht), judgment of 26 September 2019 - 7 C 5.18 - (...) para. 17 et seqq. with further references). It is therefore already to be examined in the context of admissibility whether the contested decision or the contested plan is one of the decisions or plans for which there may be an obligation to carry out a strategic environmental assessment under the Environmental Impact Assessment Act (see BVerwG, judgment of 19 December 2013 - 4 C 14.12 - Rulings of the Federal Administrative Court (BVerwGE, Entscheidungen des Bundesverwaltungsgerichts) 149, 17 para. 10 on the obligation to carry out an environmental impact assessment (EIA)). This is the case here. Clean air plans are subject to an obligation to carry out a strategic environmental assessment under no. 2.2 of Annex 5 to the UVPG in conjunction with section 35 (1) no. 2 UVPG when they set a framework for decisions on the permissibility of the projects listed in Annex 1 to the UVPG or of projects which, under federal state law, require a strategic environmental assessment or a preliminary assessment of the individual case.

23 b) The specific admissibility requirement of section 2 (1) first sentence no. 3 (b) UmwRG is also fulfilled. Under this provision, in the case of proceedings under section 1 (1) first sentence no. 4 UmwRG, the standing of an environmental association requires it to have been entitled to participate and to have made a statement regarding the matter in the course of the procedure in accordance with the applicable provisions or, in contravention of the applicable provisions, it was given no opportunity to make a statement. The Senate has already decided on section 2 (1) first sentence no. 3 (a) UmwRG (BVerwG, judgment of 26 September 2019 - 7 C 5.18 - (...) para. 24) that in the case of authorisation decisions within the meaning of section 1 (1) first sentence no. 1 UmwRG, where the obligation to carry out an environmental impact assessment and thus the entitlement to participate depends on a preliminary assessment of the individual case, the possibility of an entitlement to participate is sufficient at the level of the assessment of the admissibility in order to substantiate a standing. This is transferable to the participation requirement contained in section 2 (1) first sentence no. 3 (b) UmwRG.

24 2. The actual existence of an obligation to carry out a strategic environmental assessment is also not a requirement for assessing the merits of an environmental organisation's action for the updating of a clean air plan. To this extent, section 2 (4) second sentence UmwRG, which makes a judicial review of plans and programmes under section 1 (1) first sentence no. 4 UmwRG dependent on the actual existence of an obligation to carry out a strategic environmental assessment, is not applicable. Contrary to the claimant's view, however, this does not already follow from the fact that the entitlement claimed is not, as required by section 2 (1) first sentence UmwRG, a legal remedy "against a decision pursuant to section 1 (1) first sentence". An action for performance aimed at updating a clean air plan is also targeted against a decision to approve a clean air plan (section 1 (1) first sentence no. 4 UmwRG), as such an action is only well-founded if the plan proves to be unlawful because, in violation of section 47 (1) first sentence BImSchG, it does not specify the measures necessary for the permanent reduction of air pollutant. Rather, the limited standard for assessing the merits is not applicable because a teleological reduction of the provision is required for cases of this kind. By including clean air plans within the scope of the Environmental Appeals Act, the legislature's intention was to take account of the Senate's judgment of 5 September 2013 - 7 C 21.12 - (BVerwGE 147, 312 para. 38 et seqq.) on the legal position of environmental associations as having general power of representation and transpose it into a legal provision (Bundestag printed paper (BT-Drs., Bundestagsdrucksache) 18/9526 p. 35). In this judgment, the Senate derived an extended interpretation of section 47 (1) BlmSchG from EU law, which grants a recognised environmental organisation own rights within the meaning of section 42 (2) VwGO. The Senate did not limit this expansion of the subjective legal position of associations on the basis of EU air quality law to clean air plans subject to an obligation to carry out an environmental assessment either at the level of the admissibility or with regard to the assessment of the merits. In this context, a teleological reduction of section 2 (4) second sentence UmwRG is required for actions against clean air plans by recognised environmental associations. Otherwise the legislature would unintentionally fall short of its regulatory intention as clearly expressed in its explanatory memorandum to the Act (...).

25 3. Contrary to the view of the defendant and the summoned third party, a right of the claimant for Reutlingen's Clean Air Plan to be updated is not ruled out from the outset because compliance in 2020 with the limit values set out in section 3 (1) of the Thirty-Ninth Ordinance on the Implementation of the Federal Immission Control Act - Ordinance on Ambient Air Quality Standards and Emission Ceilings (39. BImSchV, Neununddreißigste Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes - Verordnung über Luftqualitätsstandards und Emissionshöchstmengen) of 2 August 2010, Federal Law Gazette (BGBl., Bundesgesetzblatt) I p. 1065) is certain. The Higher Administrative Court's assumption that the limit value for nitrogen dioxide will again not be complied with in 2020 does not suffer from the procedural errors invoked by the defendant and the summoned third party.

26 According to the updated forecast submitted by the defendant shortly before the material time of the oral hearing at the Higher Administrative Court "(...)" an annual average for nitrogen dioxide was forecast at the (...) measuring station of 48µg/m³ for 2019 and 44µg/m³ for 2020. At the same time, the summoned third party claimed in the oral hearing before the Higher Administrative Court that photocatalytic facade coatings on Lederstraße and moving the road by one metre would be likely to reduce immissions by 3µg/m³. It claimed that implementing measures from the Clean Air Plan and further measures was likely to lead to a further reduction of more than 1µg/m³, resulting in compliance with the limit value in 2020.

27 a) The participation and disclosure requirements of clean air planning do not conflict with the updating of the forecasts and the measures (...). The obligation for public participation contained in section 47 (5) and (5a) BImSchG does not preclude revision and review, limited to updating, of the forecasts on which the planning is based and the measures contained in the clean air planning. Something different may apply if forecasts are made using a completely new method or planned measures are fundamentally redesigned.

28 b) The Higher Administrative Court reached the assumption without breaching the law that the reduction effects of further clean air measures cited by the summoned third party at the oral hearing did not provide plausible evidence for the assumption that the value for 2020 as a whole would be below the annual average. The Higher Administrative Court's assessment, that the reduction effect of 3µ/m³ caused by the photocatalytic paint in the updated forecast was not reliably substantiated, is not based on facts established contrary to the files. (...)

30 4. The Higher Administrative Court wrongly assumed that the defendant, by not issuing any traffic bans for 2019, had already infringed the obligation contained in section 47 (1) first sentence BImSchG to draw up a clean air plan if immission limit values established by an ordinance issued pursuant to section 48a (1) BImSchG are exceeded. According to the Higher Administrative Court's factual findings, which were not challenged by procedural complaints, traffic ban orders for diesel vehicles could have enabled compliance with the limit values for nitrogen dioxide area-wide already in 2019. The Higher Administrative Court's assumption that to avoid exceedance of the limits, traffic ban orders for diesel vehicles should not have been waived does not take sufficiently into account the principle of proportionality, however.

31 In the present case, according to the original forecast underlying the Clean Air Plan, the NO₂ value at the (...) measuring station should have amounted to 41μg/m³ in 2019. The Higher Administrative Court relied upon this forecast. In view of this, its demand that a traffic ban for 2019 should not be waived, despite the fact that, even without a traffic ban, the limit values in accordance with the original forecast were complied with in 2020, overstretches the proportionality requirements developed by the Senate in its judgments of 27 February 2018 - 7 C 30.17 - (BVerwGE 161, 201) and - 7 C 26.16 - (...).

32 a) With reference to the case-law of the Court of Justice of the European Union (CJEU, hereinafter Court of Justice), the Senate stated that exceeding the limit values to be complied with is sufficient in itself to constitute an infringement of article 13 (1) of Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe (OJ L 152 p. 1) in conjunction with Annex XI of this Directive (BVerwG, judgment of 27 February 2018 - 7 C 30.17 - BVerwGE 161, 201 para. 32). According to this, even a possible partial downward trend in ambient air pollution, which does not, however, lead to compliance with the limit values, cannot invalidate the finding of failure to fulfil obligations attributable to a Member State (CJEU, judgment of 22 February 2018 - C-336/16 [ECLI:EU:C:2018:94], Commission/Poland - para. 62 and 65).

33 However, infringement of article 13 (1) of Directive 2008/50/EC does not yet imply an obligation to act in relation to a specific individual measure. Accordingly, the fact that in a Member State limit values in ambient air are exceeded is not in itself sufficient to establish that the Member State has violated its obligations under article 23 (1) second subparagraph of Directive 2008/50/EC. Instead, the Member States have some scope for action in determining the measures to be adopted (BVerwG, judgment of 27 February 2018 - 7 C 30.17 - BVerwGE 161, 201 para. 33 et seq.). In any case, however, the measures laid down must be suitable to keep the exceedance period of limit values as short as possible. The length of the period of time during which a limit value has already been exceeded must also be considered (see CJEU, judgment of 24 October 2019 - C-636/18 [ECLI:EU:C:2019:900], Commission/France - para. 90). Clean air plans may be adopted only on the basis of a balance between the aim of minimising the risk of pollution and the various opposing public and private interests, however (established case-law; see CJEU, judgment of 24 October 2019 - C-636/18 - Commission/France - para. 79). A traffic ban order must be subject to the principle of proportionality (BVerwG, judgment of 27 February 2018 - 7 C 30.17 - BVerwGE 161, 201 para. 38).

34 b) The Higher Administrative Court's view that the assessment of proportionality was limited to the design of traffic bans as the Federal Administrative Court had only undertaken proportionality considerations on graduating zone-related traffic bans on diesel vehicles with a Euro 5 exhaust emission standard and for lower Euro exhaust emission standards, violates federal law. The principle of proportionality claims validity not only with regard to the question of how a traffic ban is to be designed, but also with regard to the preceding question of whether a traffic ban is to be ordered. Even if an all-the-year-round traffic ban proves to be the only suitable measure to comply with the limit values for nitrogen dioxide as quickly as possible, this does not in itself make superfluous the assessment of proportionality as to whether such a ban is to be imposed at all. In accordance with the established jurisprudence of the Federal Constitutional Court (BVerfG, Bundesverfassungsgericht), the principle of proportionality requires that, at the final assessment level, a loss of freedom that is protected by the constitution is not disproportionate to the objectives with the purposes of public interest that are served by the restriction of the fundamental rights in question (see judgment of 14 July 1999 - 1 BvR 2226/94 et al. - (...) para. 221). This makes it necessary to assess proportionality in the narrower sense, also concerning the question of whether a traffic ban may be a proportionate measure.

35 Nothing else proceeds from the fact that the superordinate purpose of compliance with limit values for nitrogen dioxide immissions is to protect human health. Health protection is an exceedingly important public interest objective that is enshrined in the constitution (BVerfG, decision of 30 July 2008 - 1 BvR 3262/07 et al. - Rulings of the Federal Constitutional Court (BVerfGE, Entscheidungen des Bundesverfassungsgerichts) 121, 317 (...) para. 102). Accordingly, the state is obliged to protect and support the life, physical integrity and health of individuals (BVerfG, chamber decision of 15 March 2018 - 2 BvR 1371/13 - (...) para. 31 with further references). This is no absolute obligation, however. Insofar as the conduct of third parties is concerned, a breach of the duty to protect can only be considered if the regulations and measures taken are obviously unsuitable or completely inadequate; if they fall considerably short of the objective to protect; or if they are based on an inadequate establishment of facts or unjustifiable assessments (BVerfG, decision of 15 March 2018 - 2 BvR 1371/13 - (...) para. 32).

36 Nothing else proceeds from the obligation to act under EU law under article 23 (1) of Directive 2008/50/EC. According to the case-law of the Court of Justice, clean air plans may be adopted only on the basis of the balance between the aim of minimising the risk of pollution and the various opposing public and private interests (see CJEU, judgment of 24 October 2019 - C-636/18 - para. 86) An obligation to take effective but disproportionate measures would not be compatible with this or with the scope for action expressly given to the Member States by the Court of Justice for determining the measures to be adopted - notwithstanding the obligation to keep the exceedance period as short as possible (see CJEU, judgments of 5 April 2017 - C-488/15 [ECLI:EU:C:2017:267] Commission/Bulgaria - para. 15 and of 22 February 2018 - C-336/16 - para. 99 et seqq.).

37 c) The Higher Administrative Court's view that a clean air plan does not fulfil the legal requirements if it waives the immediate introduction of traffic bans for diesel vehicles, regardless of the amount by which and the period of time during which a value has been exceeded does not fully meet these standards. Notwithstanding any shortcomings in the forecast, traffic ban orders are not generally required when the limit value exceedance assumed by the Higher Administrative Court is only 1µg/m³ in the first year following the entry into force of the Clean Air Plan and, at the same time, the value is forecast to fall (significantly) below the limit value in the second year. In such a case, the burdens associated with traffic bans, in particular for the owners, keepers and drivers of diesel vehicles, are not proportionate to the possible risks to health associated with such insignificant and temporary exceedances of the limit value.

38 This also applies to route-related traffic bans, which, as a rule, are less burdensome. To this extent, it is to be taken into account in particular that route-related bans may lead to diversions and thus to heavier pollution on other roads. This is acceptable in principle, as the Senate stated in its judgments of 27 February 2018 - 7 C 30.17 - (BVerwGE 161, 201 para. 66) and - 7 C 26.16 - (...), insofar as limit values are not exceeded on the diversion routes. However, this does not mean that the interest of persons living along the diversion routes in preventing what may be a considerable increase in air pollutants, approaching the immission limit values, is irrelevant from the outset. If, as in this case, the limit value is exceeded within a range of just 1µg/m³ and it can be expected as a matter of certainty that the pollution will continually decline and the limit values will be complied with or even significantly undercut in the very near future, a traffic ban is generally not required, even if it is the only appropriate measure to achieve the objective at an earlier point in time.

39 Whether a traffic ban would also be deemed to be disproportionate even when limit values have been exceeded by greater amounts depends on the circumstances of the individual case, particularly the forecast duration of exceedance and the level of certainty with which compliance with the limit values can be expected. The shorter the exceedance period and the more certain it is that the limit values are likely to be complied with in the near future, and the greater the effects of a traffic ban on the road users and residents along diversion routes concerned, the more acceptable it is for limit values to be exceeded by higher amounts. For example, in a situation where a considerable reduction in traffic and thus also pollutants is to be expected as a matter of certainty in the near future on account of the imminent completion of a by-pass or road tunnel, and diverting traffic would lead to considerable pollution elsewhere, it would be tolerable from the point of view of proportionality to exceed limit values even significantly for a temporary period.

41 5. Without breaching federal law, the Higher Administrative Court objected that existing planning is based on a deficient forecast.

42 a) A lawful clean air planning must be based on a proper forecast of the development of the immission values. What is decisive is the factual and scientific knowledge existing when the plan is drawn up. In the case of planning decisions that are not only based on recording a current state, but also on estimating future facts, it is natural that a court can only review the accuracy of the forecast to a limited extent. Naturally, it is impossible to establish exactly how factual circumstances will actually develop in the future. The forecasts, which are thus not guaranteed to be accurate, can be judicially reviewed only to the limited extent that they are methodically sound, are not based on unrealistic assumptions and that the result of the forecast is plausibly reasoned (see BVerwG, decision of 28 November 2013 - 9 B 14.13 - (...) para. 7).

43 The obligation to produce results determined by EU law does not place increased requirements on judicial review of forecasts in the field of clean air planning. The parallel with the requirements for authorising projects in Habitats Directive sites developed in the jurisprudence considered by the Higher Administrative Court is unconvincing. Unlike clean air planning, the procedural and substantive requirements of the assessment of the implications for sites provided for in article 6 of the Habitats Directive (Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora) are designed in relation to projects and areas of conservation. The prohibition on authorising a project unless there is certainty that it will not have an adverse effect on the conservation objectives defined for the site is based on the special significance of the areas of conservation forming the ecological network "Natura 2000" and is not applicable to planning decisions or generalisable in any other way (...).

44 b) The Higher Administrative Court assumed, without infringing federal law, that the traffic forecast on which measures M 1 and M 2 were based had shortcomings in the area of its factual assumptions and in the plausibility of its substantiation.

48 6. The summoned third party correctly pointed out that a clean air plan is not required to hold ready any measures for the case that the forecast of compliance with the limit values proves to be too positive and it appears that it will not be realised in the foreseeable future. (...)

49 a) The requirements of section 47 (2) fourth sentence BImSchG, the only possible legal basis, have not been met. According to this provision, one part of a clean air plan may be a plan for measures to be taken at short notice. Additional measures in case the "first phase" measures fail thus do not correspond to the concept of section 47 (2) BImSchG, which only distinguishes between measures to be taken at short notice and longer-term measures according to section 47 (1) BImSchG. "Second phase" planning is therefore not planning within the meaning of section 47 (2) second and fourth sentence BImSchG.

50 b) The obligation to produce results founded on EU law and the requirement to carry out an administrative procedure in a timely manner do not require precautionary planning for the case that forecasts on which a clean air plan is based turn out to be erroneous or the measures laid down turn out to be insufficient. The competent authority has an obligation to observe the development of air pollution constantly and sufficiently closely and to monitor the effectiveness and sustainability of the determined measures. However, this does not mean that it is required to take an anticipatory look at all exceedance variants that are likely and seriously possible already when the plan is drawn up and to develop or to hold ready concepts targeted at them (...). Such a far-reaching phased assessment would require a large number of scenarios to be subjected to a complex assessment programme and, depending on the imputed extent to which targets were not met, would require reflection on different reaction concepts, and in this connection also differentiated considerations on the proportionality of any measures that may have to be held ready. As a rule, this would not insignificantly lengthen the planning period in spite of exceedance of the limit values and would counteract the requirement to carry out an administrative procedure in a timely manner in drawing up a clean air plan. This would also make it considerably more difficult to monitor compliance with this requirement. The authority can and must react to less favourable developments than forecast by timely and decisively updating the clean air plan. Contrary to the view of the summoned third party, it is under an obligation to react during the year if it becomes apparent that a forecast has been proven to be incorrect or the intended measures are not effective.

51 7. The Higher Administrative Court rightly considered a new planning to be necessary. Such an obligation already follows from the fact that the forecast on traffic reduction in Lederstraße is not reliable and the limit values at the time of the last oral hearing, the relevant point in time here, were still exceeded.

52 a) The fact that the immission limit value for nitrogen dioxide under section 3 (2) 39. BImSchV refers to a calendar year, which means that actual compliance can only be established after the end of the year, does not preclude a new planning during the current year. That does not mean that clean air planning and the measures it lays down can only start at the beginning of the year. If it has been forecast that the limit value will be exceeded in the current year and if the current planning has shortcomings, the planner must react immediately. The obligation to carry out new planning may be ruled out if, on account of the development of air pollutants in the meantime, it has been established that at the material time of the last oral hearing at the court responsible for finding the facts, clean air planning was no longer necessary (...). This is not the case here, however. The Higher Administrative Court established without procedural error that according to the updated forecasts, annual average values for nitrogen dioxide of 48μg/m³ for 2019 and 44μg/m³ for 2020 are to be assumed for the "Lederstraße-Ost" measuring station.

53 b) The Senate can leave open the question of whether the shortcomings of the forecasts continued to have an effect on the new forecasts submitted in March 2019, as the Higher Administrative Court assumed, because forecasts must be updated or new forecasts must be made when carrying out the new planning. (...)

54 c) When carrying out the new planning, the principle of proportionality must be taken into account. In the context of this assessment, it may be necessary to consider other aspects in addition to the introduction of traffic bans gradually over time and the differentiation according to the spatial scope of the bans and the age and exhaust emission behaviour of the vehicles concerned, that have been discussed by the Senate in its judgments of 27 February 2018 - 7 C 30.17 - (BVerwGE 161, 201) and - 7 C 26.16 - (...).

55 aa) The Senate has already pointed out that not only burdens and restrictions on vehicle owners, vehicle keepers and vehicle users are to be taken into account, but also the impact on the supply of the population and the economy (BVerwG, judgments of 27 February 2018 - 7 C 30.17 - BVerwGE 161, 201 para. 41 and - 7 C 26.16 - (...)). As shown in detail above, a traffic ban may be disproportionate in cases where limit value exceedance is very slight if the remaining exceedance period is only short, and compliance with the limit values is expected as a matter of certainty.

56 The balance to be made accordingly within the assessment of proportionality does not mean that an open-ended planning decision (planerische Abwägung) taking account of all possible interests must be undertaken, however. If the relevant limit value is exceeded and if a measure proves to be suitable and necessary in order to keep the exceedance period as short as possible, the balance of interests is no longer to be undertaken in the spirit of a planning decision, but as an expression of the assessment of proportionality in the narrow sense, according to which a legitimate objective may not be pursued using suitable and necessary means at any cost. In this spirit, the CJEU pointed out in its judgment of 24 October 2019 - C- 636/18, Commission/France - (para. 86) that structural difficulties were not a justification for exceeding the limits, but that they could constitute a fact that may be of significance in the context of the general weighing of interests. Such a fact may also be the specific infrastructural significance of a traffic route (...).

57 In contrast, no factual findings are required on the type and extent of risks to health resulting from the exceedance of limit values. The measures necessary for the attainment of limit values in the course of planning must not be relativised in the context of balancing the extent of risks to health resulting from the exceedance of limit values against the restrictions on road users resulting from traffic bans. Therefore, a detailed determination of the exact degree of concernedness caused by risks to health and the number of persons concerned is not required (...). The legislative body has already taken the fundamental decision on the question of risk to health when limit values are exceeded; thus, this question is not subject to review in individual cases.

58 8. No further restrictions to the considerations on the principle of proportionality stated above arise from section 47 (4a) BImSchG. In accordance with this provision, traffic bans on diesel vehicles on account of exceedance of immission limit values are generally only possible in areas where the annual average value for nitrogen dioxide has exceeded 50 micrograms/m³.

59 a) Without breaching federal law, the Higher Administrative Court assumed that the only measured exceedances of limit values of up to 50 micrograms of nitrogen dioxide per cubic metre of air have to be taken into account and not merely forecast exceedances of this amount. It would be difficult to reconcile a different understanding with the wording of the provision. Even if one were to base an understanding on the purpose of the provision, despite the clear wording, nothing else would follow. It can neither be inferred from the explanatory memorandum (BT-Drs. 19/6335) nor from the opinion by the Committee on the Environment (BT-Drs. 19/8257) that the legal assumption underlying the provision that wherever nitrogen dioxide pollution is already less than 50µg/m³, it is to be assumed that the measures adopted will lead to a reduction below the limit value should also apply where the measured pollution was previously higher than 50µg/m³ but immission forecasts refer to lower future values. Nothing else follows from the example described by the defendant. If at the time the clean air plan is drawn up, the last measured pollution is still more than 50µg/m³, favourable developments in individual cases may exist, which result in reducing it by more than 10µg/m³. However, this is neither likely to correspond to previous experience of the development of immission values, nor did the legislature formulate such an expectation.

60 b) The provision that traffic bans for diesel vehicles are generally only possible when values are higher than 50µg/m³ is to be interpreted in conformity with EU law to the effect that it is intended to express a factual presumption that when there are such immission values, the measures taken are likely to lead to the limit value being undercut in the near future, even without traffic bans To the extent that, contrary to this assumption, this is not the case, and traffic bans are the only means to keep exceedance of the limit value as short as possible, a standard case within the meaning of section 47 (4a) BImSchG cannot be assumed, however, so this provision cannot be used as an argument to oppose traffic bans in the context of the principle of proportionality, even when values are below 50µg/m³.

61 As the Higher Administrative Court correctly assumed, an interpretation that might be more obvious on the basis of the wording - that the intention was to create a genuine rule-exception relationship according to which traffic bans may only be ordered in atypical cases - is not compatible with EU law. The legislature is free to determine by law requirements for the assessment of proportionality. However, a rigid limit below which a type of measure recognised to be effective could only be ordered in an atypical exceptional case would breach the obligation under EU law to keep the exceedance period as short as possible. This obligation in turn is subject to the principle of proportionality. However, it may be assumed from the CJEU's case-law that general considerations not related to individual cases may not be used as evidence that the measures taken were sufficient, particularly in the case of lengthy exceedance, and that the limit values continue to be exceeded (see CJEU, judgment of 24 October 2019 - C- 636/18, Commission/France - para. 84). This is confirmed by the European Commission's comments upon notification of the 13th Act Amending the Federal Immission Control Act, which welcome the wording "as a rule", "in order not to rule out traffic bans if they should prove to be the only way to keep periods of non-compliance as short as possible" (...).

63 There is no reason to refer the question on the compatibility of section 47 (4a) first sentence BImSchG with article 13 or 23 of Directive 2008/50 EC to the CJEU. Rather, on the basis of the case-law of the Court of Justice in recent years, the interpretation of the relevant provisions of the Directive is sufficiently clear to arrive at the interpretation in conformity with EU law outlined above (...).

64 c) Unconstitutionality of the amendment (...) does not arise from the fact that the regulatory effect of the assumed interpretation in conformity with EU law is small in comparison with the principle of proportionality which applies in any case (...). The legislature is not prevented from codifying a situation arising from jurisprudence and general legal principles. The principle that legal norms are "genuine", that is enforceable and enforced (Normenwahrheit) means that the legislature must be bound by the regulatory content discernible by the person to whom a legal provision is addressed. However, it is sufficient for this content to be discernible by means of interpretation in a way that may reasonably be expected (see BVerfG, decision of 2 June 2008 - 1 BvR 349/04 - (...) para. 23). This is the case here.

65 d) Following the above considerations on proportionality in the narrow sense, it does not appear mandatory for traffic bans to be ordered on the basis of the Higher Administrative Court's factual findings. They are to be assessed by the planner and ordering them in the clean air plan is to be seriously considered. Whether they prove to be proportionate in consideration of all the circumstances that must be taken into account requires a renewed assessment. If the planner concludes that they are disproportionate in spite of their suitability and necessity for compliance with the limit values, this requires a detailed reasoning (...).