Facts
The canton of Vaud, the regional associations and the municipalities concerned developed the Lausanne-Morges agglomeration project (PALM). An agreement was signed on 22 February 2007 and submitted to the Confederation. In May 2008, the Cantonal Council of State of Vaud adopted investments including the Renens-Flon tram and several trolleybus sections on dedicated right-of-way.
By request of 15 March 2010, the Transports publics de la Région lausannoise SA (the TL, transport company) asked the DETEC for a concession for the construction and operation of the tramway line 'Renens-Gare - Lausanne-Flon' (t1). During the proceedings, the TL requested the inclusion of a new road link between the rue de la Vigie and the avenue Jules-Gonin (Vigie-Gonin link). By decision of 16 September 2011, the Federal Council granted concession no. 5146, valid from 1 January 2012 to 31 December 2061, subject to certain conditions, in particular concerning deforestation.
On 22 May 2012, the TL submitted to the Federal Office of Transport (OFT) an application for approval of plans covering three components: the tramway t1 (including the Vigie-Gonin link), the high-service-level trolleybus (BHNS) 'Prélaz-les-Roses - St-François' and the 'Perrelet' depot-workshop. The ordinary procedure was opened on 30 May 2012. The public inquiry drew 126 objections, including those of A., B. SA, C. SA, D. Sàrl and E. Sàrl. The canton of Vaud requested the withdrawal of the municipal library planned under the Vigie-Gonin link, which was done in September 2013. Several amendments followed (2013, 2015, 2016), and a conciliation on 2 June 2015 did not succeed.
By decision of 7 March 2016 (approval decision, DAP), the OFT approved the project. It considered itself competent to approve the plans of the Vigie-Gonin link, declared A.'s objection inadmissible and dismissed those of the opposing companies and Sàrl.
The Federal Administrative Court (TAF), by judgment of 2 February 2018, held that the plans of the Vigie-Gonin link had not been formally approved, as they did not appear in the operative part of the decision and did not bear an approval stamp. It did, however, admit the appeals concerning deforestation, finding that the OFT was not competent to approve it (a cantonal procedure being required), and annulled the expropriations linked to the road link. The TL appealed to the Federal Supreme Court against this judgment.
Central question: must the Vigie-Gonin road link be classified as a railway installation (art. 18 para. 1 RailA) or a trolleybus installation (art. 11 para. 1 LTro), falling under the single federal plan approval procedure, or does it fall under cantonal law?
Considerations
The Federal Supreme Court first examines whether the OFT was competent to approve the plans of the Vigie-Gonin link under art. 18 para. 1 RailA, a question of federal law (art. 106 para. 1 FSCA). Installations serving exclusively or principally the construction and operation of a railway may only be established after approval of the plans by the federal authority (art. 18 paras. 2 and 3 RailA), cantonal law being taken into account only insofar as it does not disproportionately impede the undertaking (art. 18 para. 4 RailA). Ancillary installations, by contrast, fall under cantonal law (art. 18m RailA). According to case law, the decisive factor is the necessary and close material and spatial connection with railway operation, and more precisely the main objective pursued by the installation, not merely the extent of the road or railway modifications. For mixed constructions, a single procedure is in principle applicable.
The Federal Supreme Court notes that the TAF recognised the link with the railway project, but considered it insufficient because of the distance (approximately 150 m), the absence of connection with the infrastructure of the t1 or the BHNS, the openness of the structure to all users and the need to guarantee the Chauderon-Sud junction. This assessment is disputed and cannot be followed.
As regards the material link, the Vigie-Gonin link is dictated exclusively by the dedicated right-of-way of the public transport lines, required by the concession. It is not disputed that the current road network cannot absorb the transfer of individual motorised traffic (TIM) resulting from the closure of the rue de Genève and the rue des Terreaux. The construction of the structure therefore constitutes an accompanying measure necessary for the principal element of the project, the two public transport lines on dedicated right-of-way, and not a measure imposed by road requirements. The road character of the structure, used by all users, is not sufficient to remove it from the railway regime.
As regards the spatial link, although the structure is located approximately 150 m from the railway alignment, the avenue Jules-Gonin is the closest parallel axis for redirecting TIM directly from the section…