Frankly it's almost criminal for a very narrow two-lane bridge built in 1878 to reach a point where it is carrying 25,000-vehicles per day without amplification or replacement. There are sections of the Western Highway being duplicated west of Ballarat that only carry 6,000-vehicles per day. I would see the need for a second bridge across the Murray in the Echuca region as urgent rather than a boondoggle, rail underutilisation or not.
No. I reckon the economics and the traffic considerations are nonsense.
Almost all of the traffic over the existing bridge is local to Echuca/Moama; it's not through traffic.
From a daily perspective, the traffic only gets bad in the morning and evening peaks as people come and go from jobs/shopping in Echuca. I can understand that it would get irritating from a country perspective, but it's a minor blip compared with driving anywhere in Melbourne, or even a rural city. How minor the traffic levels are can be judged by the fact that the major intersection at the south end of the bridge is still a roundabout - no traffic lights.
Traffic levels would only reach 25,000 vehicles a day in peak summer holiday season when the resorts around Moama are going gangbusters. And, of course, almost all of these vehicles would be cars, well within the capacity of the bridge.
To be honest, it's not clear to me how much traffic the new bridge would capture. The new bridge is west of the Campaspe River, most of the traffic sources/sinks are east of the river in Echuca proper, and there are only two bridges across the Campaspe: Warren St and the Murray Valley Hwy. Any traffic down Warren St has to go along High St - there is no alternative. High St is the main tourist drag. Not only is this a high pedestrian area, but, it's a 50 km/h two lane road, and during the day the traffic in this section is already bumper to bumper. It has no capacity to absorb any more traffic. The Murray Valley Hwy has plenty of capacity, but is well south of the centre of Echuca and would be a detour for most traffic.
(I would note that when I last stayed in Echuca at the beginning of the year, Warren St was being rebuilt - it's clear that VicRoads/the local council expects traffic to increase on this route.)
The new bridge would get the trucks out of the centre of Echuca and Moama, and save them 15 or 20 minutes, but whether it is worth spending the money just for that is another matter. You could get them out of the centre of Echuca by upgrading the road to the east of the railway station down to the Murray Valley Hwy for a fraction of the cost of a new bridge.
I forget to comment on the politics. While this was a Victorian announcement, remember that NSW would be kicking in the same amount as Victoria, and the Feds would also be contributing. NSW and the Commonwealth governments are both conservative, matching the political complexion of the electorates. Most of the benefit of the bridge would be to NSW residents - particularly Deni - so I could understand the interest of that government.
It's also a good example of the persistence of infrastructure proposals. A second bridge has been on the wish list of the area for a long time. They don't have to pay for it, so it's a continual local demand.