The video, posted to its social media, shows work well under way on the 600-metre bridge in Al Bithnah.
The bridge passes through the Hajar Mountains, with towns and farms visible in the background.
Workers are seen clearing a path for the line, assembling the concrete support pillars for the bridge and laying down the track.
In railway terminology, it is known as an "underbridge", meaning it can only be used for trains.
Etihad Rail said the bridge will act as the rail gateway to the UAE’s east coast and enable trade to and from Fujairah.
Construction for the Northern Emirates network involves building 54 bridges and nine tunnels across the Hajar Mountains. The network extends more than 145 kilometres through the emirates of Sharjah, Fujairah and Ras Al Khaimah, Etihad Rail said.
A freight service linking the gasfields at Shah and Habshan to Ruwais in Al Dhafrah opened in 2016, while a freight and passenger network will extend across the UAE, from the border of Saudi Arabia to the border of Oman.
News of the bridge comes as thousands of visitors are set to descend on Abu Dhabi next week for a major rail conference.
Middle East Rail, which is being hosted by Etihad Rail, is expected to draw 6,000 visitors, more than 200 speakers and 250 exhibitors.
The two-day event starts on Tuesday, with the conference set to shape the future of rail in the region.