Metro

It’s a rail shame if this is end of the Line

High Line II is the best argument for opening High Line III — the rail trestle’s derelict, northernmost spur, which curls around the vast West Side railyard like a friendly serpent.

If you thought High Line I ended too soon at 20th Street, wait till you stroll north on the new section. After affording so many pleasures, the drag-strip-straight park begins a long, sweeping turn west starting near 29th Street.

A “radial bench” rides the bend so naturally, you could almost believe the old freight line’s creators had it in mind all along. The curve — embellished with magnificent landscaping that obscures where it leads — seems to pull you toward a dramatic, unknown climax. (A sensational view of the railyard, perhaps?)

But no! The path ends with a chain-link fence that feels like a slap in the face. It seems almost intended to make park-goers scream for more — very possibly what City Hall and the High Line’s private backers have in mind.

Because while Mayor Bloomberg and others yesterday expressed hope that the trestle around the train yard can be made part of the park, lots of obstacles remain.

Some have to do with the future development of Hudson Yards, where the Related Cos. is slated to build large office and residential buildings atop a platform to be built over the yards. The issues are complex and will require lots of effort and good will by all parties.

Let’s hope a deal gets made. High Line II is a grand achievement, but — more than Part I did — feels as if it’s trying to get somewhere that it can’t quite reach.

Its great middle section traverses narrow notches between spectacular new buildings like shimmering 245 Tenth Ave. and haunting old ones with faded “ghost” signs.

It affords moody vistas like one facing west through an alley near 25th Street, where sheer masonry walls converge between dueling sunlight and shadow toward a distant, brooding smokestack.

But the blocks between 20th and 23rd streets and north of 27th Street, for all their magnificent landscaping and detailing, feel transitional — a fact the design features can’t hide.

Until you reach the curve. Suddenly, you sense a great and wonderful surprise lies just around the corner.

But instead comes the premature dead end. Instead of feeling elated, you feel the way you did after the last episode of “The Sopranos.”

The High Line Park deserves a proper conclusion. Bring it on!

scuozzo@nypost.com