The A4 between Bad Hersfeld and Eisenach has a very complex history. Construction begun late in the 1930s, and when WW2 broke out, it became increasingly difficult to continue working on this section. When in 1943 construction was completely stopped, the road was with the exception of some valley bridges (which had to be bypassed) usable with one lane in each direction. Only military vehicles used it, because in 1943 no civil cars were allowed anymore. Among the parts that were missing were the Richelsdorf valley bridge (the autobahn ended before the valley, vehicles had to cross the valley on trunk roads - today these trunk roads are the onramp and offramp of exit Gerstungen) and the complete section between Wartha and Eisenach including the Werra valley bridge. The Wommen valley bridge was uncompleted.
Bridge fragment near Herleshausen ca. 1980
Closed section near ca. 1980
Closed section near bei Obersuhl ca. 1980
unfinished Wommen valley bridge ca. 1980
unfinished Wommen valley bridge ca. 1980
After the war, the division of Germany into different sectors made the A4 cross the border between the american and the soviet sector three times (today this is the state border between the states of Hesse and Thuringia)
In the 1950s, the autobahn was widened to two lanes in each direction on the west german side between Bad Hersfeld and Obersuhl. So in 1968, a map of this area looked like this:

Between Obersuhl and Eisenach West no autobahn section could be used.

Travellers, who wanted to go from west to east german, had to leave the autobahn at exit Obersuhl (I think it was added after the war, because the original Gerstungen exit was located exactly on the border line - not sure about it). They had to drive through the villages of Wölfterode and Herleshausen on country roads to the border station Herleshausen, and continue driving on country roads on the east german side to the autobahn exit Eisenach-West. The west german part of this country road was upgraded to Federal Road 400 because of its importance for east-west travel.
In the 1970s, the autobahn section between Wommen and Herleshausen was opened for traffic again, so cars didn't have to drive through the village center of Herleshausen anymore. With a new treaty between West and East Germany traffic had heavily increased, and the traffic density became too much for the small village of Herleshausen.

After long talks between east and west germany, around 1980 construction finally started on the missing section between Herleshausen and Eisenach-West. West Germany gave most of the money necessary for this project, even in the east german part. At the same time this section was opened, a new border control point near Herleshausen was opened too. The section between Obersuhl and Wommen, however, was still closed for security reasons.

After the peaceful revolution in east germany and german reunification, the opening of this missing section became high priority. As fast as possible, work started on the Richelsdorf valley bridge and the road widening to 2 lanes in each direction. Finally, in 1994 this section was opened. So, the A4 was finally completed, 55 years after construction started.
Newly built valley bridge Richelsdorf after completion in 1994
Construction of the second half of Wommen valley bridge in 1993/94
Air view of Wommen valley bridge after completion in 1994

The situation today on a map:

B/W-photos by Dieter Mayer-Gürr taken from the book "Reichsautobahnen"
photos of Richelsdorf und Wommen(1) valley bridge take from road construction report 1993/1994