Actually if a comparison between road and rail traffic were to be made then it should be to compare a rail line with a motorway - fast moving traffic with limited ability to stop.
No expense is spared in constructing bridges, tunnels etc (even for cattle crossing once a month) to seperate people and animals from the traffic.
It is of course highly unlikely that with the limiited funds available for railways that crossing on the level will be eliminated in our lifetimes.
Three points here: firstly, traffic on most motorways is more frequent than trains, therefore it makes sense to have more grade-separated crossings. Crossing many railways will not result in the same risk as crossing motorways if this is done properly and by the rules, despite many potential hazards, because many railway crossings simply do not have the same traffic frequency, and engineers et al have installed crossings on railways for specific reasons at specific locations - but they haven't put them on motorways. Secondly, traffic on busy motorways can come to a standstill at a rate of one mile of stationary traffic a minute, and in dry conditions any road vehicle which has been properly maintained will probably stop in a far shorter distance than a train travelling at a similar speed and in similar conditions, but this is largely irrelevant except as a point of interest. Thirdly, expenses are often spared in constructing interchanges for roads which carry vehicles travelling at similar speeds to those on motorways, but which are not in fact classed as motorways. Large and complex road junctions often catch the eye, but they are not prevalent anywhere and often they are not well-designed either. By and large, crossing even moderately busy railways can be done safely and efficiently, and railways are shown by many sets of statistics as safer than road transport.
(Naturally, very busy railway lines often avoid non-separated crossings, for completely understandable reasons. Also, as we know, a level crossing with few train services passing over it can also be very dangerous, as can a road with little traffic.)
This is besides the point rather, but I hope you don't mind me mentioning this. I don't want to start an argument. This is predominantly a thread discussing an absolutely tragic incident which does bring to light the hazards of crossings, even when they are well-maintained and considered to be reasonably well-designed.