News: SHoP Architects and SOM are among four firms putting forward their visions for the future of New York's Pennsylvania Station and Madison Square Garden (+ slideshow).

In an event at the Times Center last night, the Municipal Art Society of New York also unveiled proposals by Diller Scofidio + Renfro and H3 Hardy Collaboration Architecture, each reimagining the rail hub and the indoor arena that sits atop it.

SHoP Architects proposes to expand the main hall of Penn Station into a bright and airy space surrounded by new parks and amenities. An extension of the High Line – the New York park built along a section of a former elevated railway – would connect the station to a new Madison Square Garden offsite.

Skidmore, Owings & Merrill LLP (SOM) put forward a huge expansion of the station centred around a central, transparent ticket hall. Floating above it would be an inverted dome containing offices, apartments and green spaces staggered over multiple levels.

The proposal by Diller Scofidio + Renfro suggests moving Madison Square Garden across Eighth Avenue and expanding Penn Station upwards to include new amenities such as a theatre and spa.

Finally, H3 Hardy Collaboration Architecture proposes shifting Madison Square Garden to a 16-acre platform over the Hudson River at 34th Street, creating cycling and pedestrian promenades and a new 16-acre park.

The competition was launched to encourage discussion about the future of the site, which seems increasingly uncertain. While the owners of Madison Square Garden have asked to renew their permit for the site above the station "in perpetuity", the New York City Planning Commission recently voted to limit it to 15 years, placing a question mark over the arena's future.

Penn Station, which was designed to accommodate around 200,000 passengers a day but now has to deal with around 640,000, is seen by many New Yorkers as inefficient and badly in need of an update.

Last year the Municipal Art Society invited architects to suggest improvements to New York's Grand Central Terminal, with SOM coming up with a floating observation deck that slides up and down and Foster + Partners proposing to increase the station's capacity.

Other railway stations we've published include a Spanish station with a faceted aluminium interior and the vaulted concourse by John McAslan + Partners at King’s Cross Station in London – see all stations and transport hubs.