JR East has been working since 2008 on a new line to connect Ueno and Tokyo stations: the Tohoku Jukan Line (literally the "north-east longitudinal" line) .
Ueno and Tokyo are already connected by the Keihin Tohoku Line (which curves through Tokyo from Omiya up north down to a little past Yokohama) and Tokyo's loop line, the Yamanote Line. However, people coming from up lines that connect the north have to change at Ueno to the Keihin Tohoku Line or the Yamanote line to get to Tokyo, making for a lot of congestion on that stretch of those lines.
There are three main lines that join Tokyo with the rest of Honshu, which end at Ueno Station.
The Joban Line runs from Iwanuma Station, way up on the north coast of Honshu, all the way down (except for the section betweeen Hirono and Haranomachi in Fukushima, closed since the 2011 earthquake) to Ueno and then Nippori in Tokyo, although more Joban line trains leave from Ueno than Nippori.
The Takasaki Line begins NNW of Tokyo, in Takasaki, runs to Omiya station, and is connected to Ueno station via the Tohoku Main Line.
The Utsunomiya Line is the section of the Tohoku Main Line between Kuroiso Station in Tochigi, NNE of Tokyo, and Ueno Station.
With the construction of the new Tohoku Jukan Line, passengers coming to Tokyo on these three lines will now be able to go all the way to Tokyo Station (and beyond) more quickly and smoothly than before.
The Tohoku Jukan Line is a stretch of track between Tokyo and Ueno stations about 2.5km long. It's actually not new, but a re-laying of tracks that used to exist before, but had a 1.3km gap put in them in 1991 to accommodate the Tohoku Shinkansen line when it was extended from Ueno to Tokyo. The Tohoku Jukan Line will close that gap by being piggybacked on that stretch of the extended Tohoku Shinkansen line.
I cycle to work every day along Yasukuni-dori Street, and pass under the Hiranaga rail bridge which carries Yamanote line trains between Akihabara Station just 200m to the north and Tokyo Station just 400m to the south. Running parallel to it, separated by just a few meters, is the Tohoku Shinkansen line bridge, also spanning Yasukuni-dori.
Since a few months ago, the "piggyback" track of the Tohoku Jukan Line on top of the Tohoku Shinkansen line has become visible as the construction has slowly made its way from the Tokyo Station direction towards Ueno Station.
Pictured here is the state of the construction about three weeks ago, on April 29. The huge green steel contraption on top is the "piggyback" line comprising the work.
The Tohoku Jukan Line is due to be completed next year, 2014. It is estimated to end up costing about 4 billion yen, or roughly USD400 million at today's exchange rate.
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