Snow affecting colour light signals.
If/how snow affects these in my experience, it depends on the type of snow and the direction of the wind. Also on the type of signal.
For main aspect signals on posts, brackets or on a gantry:
Ice cold (so called “dry”) snow doesn’t tend to stick on the lenses or build up on the hoods as long as there is some wind.
Wet snow however can, if the wind direction is ‘right’ can stick on lenses and may build up on hoods.
However, if enough light can still make it through the coating of snow, generally drivers don’t notice unless they have to stop at a signal or are passing the signal slowly.
Ground mounted signals, such as GPLs or ground mounted main aspect heads are far more likely to be affected. In part due to the snow being blown around by the trains as they move.
Is there a danger that snow blocks points mechanisms? Presumably, if the points are not fully in position, the protecting signal will show red.
If the point operating equipment is unable to detect that the switch rail is in the correct position, then no position will be indicated to the signaller and the interlocking will prevent any signal from showing a proceed aspect over the route that the points apply to, or adjacent route (point to point locking, flank protection etc.).
I would assume so, clearly less of a risk if point heaters are installed and working correctly.
That's the reason that many modern installations have point heaters, to melt ice and snow (if the heaters are working, of course). During falling snow, traditional mechanical signalling rules require regular movement of points required for operation of services, to prevent build up of snow in the blades.
Nearly all modern power operated point operating equipment has electrical heaters to reduce the likelihood of snow or ice causing problems. Note this is for the point operating equipment only.
Many points also have electric heating to heat either the chairs or both the stock rails and the switch rails. This is normally fitted at major junctions, junctions where one passenger line joins another and where the powers that be have decided it’s a requirement. Not all branch lines, loop points (including on main lines) or freight lines are fitted. And it’s uncommon for points for or in sidings to be fitted.
The electric point heaters should keep the points free of snow and ice for most weather conditions seen in Britain.
Points that are not fitted with electric heaters, if used regularly, may not experience problems. Ice is more of a problem than snow. However, if some snow gets compressed, it may turn to ice. Or if the snowfall is heavy or continuous, yes, eventually it may cause problems. Typically it builds up and turns to blocks of ice on the slide chairs (against the stock rail) and prevents the switch rail from fully fitting up to the stock rail. Then the point operating equipment won’t be able to detect that the switch rail has completed its movement (because it’s fowled). The type of snow and the wind direction are also factors. As is the type of point operating equipment and the length (maximum permitted speed) of the points (turn out). Clamp locks (and related) systems in my experience perform worse in winter weather.
Note that the modern design of the electric rail heating systems are fully automatic and switch themselves on when needed.
