A / In the UK, level crossing requirements , like road signage , are legislated. In Australia, level crossings and road signs are by regulation , there is a significant difference here. Legislation requires an Act of Parliament to amend. Regulation is authorised by the Governor in Council under existing legislation.
Europe , like the UK, has a different legislative stance, and a higher population, and therefore a higher road traffic density than Australia , hence the different approach to level crossing protection.
B / whether a boom barrier is manually or automatically initiated, the problem remains the same , once initiated , the full sequence has to be completed before the barriers will raise . If a motorists decides to run the lights after initiation , there is a reasonable chance of the booms being struck , hence the reason for the bells and flashing lights operating prior to the booms lowering.
Obviously, a manually operated level crossing will not have the protecting signals, where provided , placed to proceed until such time as it is safe to do so. However, most boom barrier installations are automatic in operation, and most automatic boom barriers are not protected by fixed signals ,hence the reason for the"Keep Crossing Clear" signage.
From practical experience of manual boom barrier operation , once the bells and lights start operating , motorists on the crossing usually keep going , and those who have not entered it stop to the rear of the boom ( Lotus Elan's excepted ! )
In the UK, whilst some level crossings may be remotely monitored , this does not necessarily imply that such level crossings are interlocked with protecting signals , and a lot of level crossings in the UK are not monitored at all , in which case the oversight , or lack of , is no different to what it is in Australia. It should also be pointed out that boom barriers in Europe that only close of half the road like Australia , also work automatically as they do in Australia.
The difference between Europe, the UK and Australia , is that Europe and the UK have a greater variety of level crossing protection than we do in Australia , and that is most likely due to the prior history of the level crossing in question , and the safety requirements in different locations in Europe and the UK have clearly influenced the design in use at each location . Australia, by contrast, seems happy with its current set up.
Whether the booms are equipped with skirts or not , will not , of itself , deter the motorists who decides to run the lights . From the few pictures I have seen of skirted boom barriers , the adjacent railway appears to be also fenced off , and in some cases to also have cattle grids on either side of the roadway , in which case , barrier skirts are probably a requirement for livestock control .
Contrast this with many Australian boom barrier locations not having fencing separating the adjacent railway . In most instances, cattle grids are not provided on Australian railways due to farmers with livestock being required to have their properties safely fenced off . This is not necessarily the case in Europe ( Switzerland comes to mind ) where some countries do not have fenced of grazing fields , presumably due to heavy winter snow falls.
D / In the case of the US , the length and speed of US freight trains means the time the level crossing is closed to road traffic can appear to be excessive , and relatively low traffic levels can quickly build up the traffic queues , if you look at some of the YouTube footage , roads that I would consider to be relatively low traffic seem to quickly build up a queue of traffic . I presume the this is also dependent on the spacings of adjacent level crossings , and unlike Australia, the railroads have no obligation to fund level crossing removals as US railroads have "eminent domain" so if a community wants to abolish a level crossing, well they need to stump up the cash , as the railroad is highly unlikely to do so.
In Australia, on the other hand, railway lines are still government owned and funded , and therefore level crossing removals have a political imperative that is probably greater than is the case in the US.
G / The reality is , the current standard for level crossing protection is unlikely to change in the near future , as the current standard generally works well, and level crossing accidents are relatively rare , which is why the occasional level crossing accident makes the news , unlike most road accidents, even some fatal ones, barely get mentioned, unless it is a particularly bad event.
It is noticeable to, that the various motoring organisations in Australia tend to argue for grade separation, and not argue for upgraded boom barrier protection , which implies that they think the current level crossing arrangements are satisfactory.