I don’t actually know what Network Rail has to apologise for. As I have said in answers to questions on this topic before, the vast, vast majority of accidents on level crossings in the UK are due to road user misuse.
There are over 6,000 level crossings, of many different types, in Great Britain. On average, there are 9 deaths, 7 major injuries and 23 minor injuries on them each year. The average number of deaths represent about 0.3% of all road deaths. Well over 90% of incidents involving death or serious injury on level crossings are attributable to user error, meaning that on average less than one death per annum can be attributed to the design or operation of the crossings themselves.
Whilst any death of course is regrettable the capital cost of converting a level crossing to a separated arrangement is enormous (on average about £1m a throw). There are far more accidents involving (for example) pedestrians at traffic-light controlled crossings or between cars at uncontrolled flat junctions and these incidents have various causes but could probably, in the main, be avoided. But nobody is suggesting the elimination of those situation at enormous cost.