IMHO, level crossings (and heavy trucks using them) are currently the single greatest risk for rail accidents in Australia. This is especially true in the country. This is a particular problem in Victoria as we have a relatively large passenger network, hence the risk to passenger trains is relatively high.
And the level crossing count is being reduced.
Boom barriers are an extremely effective mechanism for mitigating this risk (note: not eliminating it, as Dandenong South showed). This is because the booms are an excellent signal for road traffic - far better (IMHO) than the flashing lights during daylight. They are easily seen when vertical, the movement to horizontal attracts attention, and drivers have a reluctance to drive through a physical barrier when they are horizontal.
The wheel operated gates we used to have on level crossings near signal boxes were more effective for mitigating this risk. In addition to interlocking with protecting signals, they covered the full road width on train approach so it was impossible to zigzag around them.
IMHO, extending boom barriers to more crossings is probably the single most effective thing the government can do to reduce risk. The barrier to doing so is cost, both the initial installation and ongoing operating/maintenance costs.
Reducing the number of level crossings would help. Some level crossings with very light road traffic might as well be converted to user worked gates or barriers.
In proposing full barriers, you are proposing to very substantially increase the installation, maintenance, and operating costs. The resulting increase in safety at *that* level crossing is (again IMHO) relatively minor. Again, IMHO, the government would get a far better safety benefit by using the same money to equip more level crossings with half barriers.
How much would be increased with having twice as many barriers. These barriers would cover the footpath as well as road between them, so no need for separate pedestrian gates.
Being operated by a person who can see the crossing means that no emergency exist gates for pedestrians would be needed either.
On a narrower road, a full barriers crossing might only need two barriers, like those on a half-barrier crossing, only longer and skirted.
How did replacement of swing gates with automatic half-barriers effect maintenance costs. Hand gates weren't interlocked with signals and lacked secure lockings and so replacing them with automatic half-barriers may have increased safety despite the hand gates covering the full road width.
But I suspect that replacing interlocked gates by those half-barriers would have decreased safety.
A couple of final points. We're never going to be able to afford to equip all crossings with boom barriers. A truck/train collision could happen at any occupation crossing. So we're not going to be able to eliminate the risk using boom barriers. But we can equip crossings with poor sighting and even a low level of truck movements.
Maybe if we reduce the number of crossings we could fit booms to all the ones that remain.
Finally, if you are looking at safety, IMHO the money spent on level crossing elimination in Melbourne would have been far better spent on boom barriers in the country. But these eliminations were never about safety. They were about reducing road congestion and road vehicle wait times. Full barriers would substantially increase both.
Some of them, such as the Caulfield-to-Dandenong ones, are about unlocking rail capacity.
If we had fewer level crossings, all on the least busy lines, then full barriers could be used without creating more traffic problems.
Actually, at level crossings where road traffic is very light, full-barrier crossing maintenance costs can be reduced simply by keeping the barriers closed by default. This also makes it easier for the person operating the crossing to keep an eye on every road user crossing at that location.
Suppose we reduce the number of level crossings, this itself having priority over all other road projects, and fit controlled full barriers to the ones that remain.