Facts

B. is the owner of the neighboring parcels KTN 64 (10'000 m2, undeveloped) and KTN 229 (9'375 m2, built over with commercial buildings) in the municipality of Altendorf. Both lie in the industrial zone (noise sensitivity level IV) between the railway line to the north and the cantonal road to the south.

The Municipal Council of Altendorf publicly displayed the partial zoning plan Stoglen together with an amendment to the building regulations. Among other things, it provided for rezoning parcel KTN 64 into the residential and commercial zone of 4 storeys (WG4, noise sensitivity level III) and for a development plan requirement for KTN 64 and KTN 229.

[A.], a condominium owner of a nearby property, lodged an objection, which the Municipal Council rejected by decision of 26 September 2016. The Government Council of the Canton of Schwyz dismissed the appeal on 22 August 2017, insofar as it was admissible. The Administrative Court of the Canton of Schwyz upheld the appeal by decision of 24 April 2018 only as to costs and dismissed it in all other respects.

The eligible voters adopted the partial revision on 25 February 2019. The Government Council approved the partial development plan Stoglen on 14 May 2019. The Administrative Court notified the approval decision on 27 May 2019 and found that there was no reason for substantive coordination with the decision of 24 April 2018.

On 5 July 2019, [A.] filed a public law appeal with the Federal Supreme Court against the decisions of 27 May 2019 and 24 April 2018 and requested that the rezoning be refrained from. The Federal Office for the Environment (FOEN) filed a statement of response dated 11 June 2021.

Subject matter of the dispute was solely the rezoning of parcel KTN 64 from the industrial zone (ES IV) into WG4 (ES III). The appeal alleged a violation of Art. 24 para. 2 EPA and Art. 30 NAO. The appellant argued that when converting a noise-insensitive use into a noise-sensitive use, only Art. 30 NAO applies.

Findings on development: Parcel KTN 64 was roughly serviced with regard to access, but it still had no internal development road and no internal supply and disposal lines. Adequate development was to be demonstrated only in the development plan. The building zone was therefore considered not yet serviced within the meaning of Art. 24 para. 2 EPA and Art. 30 NAO.

Feasibility study: A feasibility study dated 20 November 2017 concluded that the planning values for railway noise could largely be complied with using a 2 m high noise barrier and noise-optimised floor plans, and that for road noise they could be complied with through office use on the road side or a noise barrier. The Administrative Court considered the study sufficiently plausible. The FOEN, by contrast, criticised considerable uncertainties and missing information (distances, calculation algorithms, number of tracks, share of heavy traffic, building orientation, sketches without noise sources and parcel boundaries). The municipality left open whether the reservations were justified.

Considerations

The noise-protection requirements for development must also be taken into account when unserviced land is to be rezoned. A rezoning into a building zone that subsequently may not be serviced under Art. 24 para. 2 EPA is inadmissible, because it is unsuitable within the meaning of Art. 15 EPA. The exception in Art. 24 para. 1 sentence 2 EPA does not help in this case.

Art. 30 NAO merely specifies and details Art. 24 para. 2 EPA and contains no deviating or stricter requirements. Both provisions concern the admissibility of developing existing building zones from a noise-protection perspective. The differing wording does not establish different situations. The lower court therefore correctly applied both provisions. The appellant's complaint is unfounded.

In multi-stage spatial planning, noise-protection measures need only be binding at the stage that permits the building permit without further planning. Already at the first stage, however, it must be established that a…