Where's the dualling for the Highland main line?

A £3billion project has been started to dual the notorious A9 Perth-Inverness road, due for completion in 2025. This has been long campaigned-for by the road lobby, but is it really necessary? Yes the road is busy, but even in summer, it's not that busy. I've driven it many times and have never been stuck in traffic, except at road works. Meanwhile the parallel railway line is still single tracked in places and still features Victorian-era semaphore signalling. So where's the dualling for the Highland main line? If the railway was improved, it could take some of the traffic off the road, making it less busy and reducing the need for dualling, and it would also help the environment at the same time. The government should prioritise rail over road improvements to get people out of their cars (and freight off lorries) and onto trains.