A long bridge over Madi river in Damuli is the longest bridge in Prithivi Highway (Kathmandu-Pokhara highway). I can’t remember the total length of the the 9-span bridge (I hope somebody will post it in comment) .
UPDATE – With thanks to Ajay ji in comment – the length of the bridge is 370m.
Another beautiful photo of the bridge shows the majestic Machapuchre and Annapurna range in the background. (I don’t know who took this photo so couldn’t credit the photographer.)
The picture above was taken from Google map – an areal view of the bridge. 
Photo credits – Sanjay Roy (last photo), Puspa Aryal (first photo)
Google map embed:
the length is 370m.