AWS and Speed Limit decrease

[Inversnecky]

We know about Morpeth boards and permanent AWS alerts before significant speed limit decreases (30% of final), but were there other occasions where AWS magnets were located ahead of general lower speed signs (eg the usual 5/10/15 mph)?

On another forum, a contributor who states he was a former driver was insisting that he encountered AWS alerts before any/all speed decreases.

Was this true, at least somewhere on the network regions, at sometime in the past, or is this simply a case of misremembering after many years?

I can’t see why you’d need alerts for every change of speed: the important alerts would be diminished by the fog of the mundane.

 

[edwin_m]

I don't believe this ever happened but I can't offer any evidence.

I seem to recall the rules for fitting speed decreases were tightened up at least once, possibly after the later Morpeth accident in the other direction where the speed dropped in several smaller steps rather than one large one, and didn't qualify for AWS under the original rules.

The criteria for setting a curve speed limit are essentially about comfort - passengers would become upset (literally in some cases) long before there was a risk of the train overturning or flange climbing or the track being pushed out of alignment. There are also considerations of track wear if trains overspeed routinely. So an occasional fairly significant overspeed doesn't have serious consequences, and I suspect that was the reason for the 30% threshold.

 

[hexagon789]

We know about Morpeth boards and permanent AWS alerts before significant speed limit decreases (30% of final), but were there other occasions where AWS magnets were located ahead of general lower speed signs (eg the usual 5/10/15 mph)?

I understand that is simply the minimum requirement, so there may will be locations where AWS is provided for a Speed Restriction Warning Board where the speed reduction is less than 30%.

 

[Efini92]

We know about Morpeth boards and permanent AWS alerts before significant speed limit decreases (30% of final), but were there other occasions where AWS magnets were located ahead of general lower speed signs (eg the usual 5/10/15 mph)?

On another forum, a contributor who states he was a former driver was insisting that he encountered AWS alerts before any/all speed decreases.

Was this true, at least somewhere on the network regions, at sometime in the past, or is this simply a case of misremembering after many years?

I can’t see why you’d need alerts for every change of speed: the important alerts would be diminished by the fog of the mundane.

IIRC the need for an aws warning for a PSR is if the linespeed is over 60mph and it’s at least a 33% reduction.

Ive never been anywhere where every reduction in speed is provided with a warning.

 

[Taunton]

Significant speed reductions on the GWR/WR were provided with a fixed distant, which in turn meant an ATC ramp and thus a warning. Likewise for a significant permanent way slack the distant would be left on, giving the same.

 

[edwin_m]

The report into the 1984 Morpeth accident: DoT_Morpeth1984.pdf (railwaysarchive.co.uk):

 

[Railsigns]

An enhanced form of continuous route signing was introduced on some routes from 1988. Amongst other things, it entailed the provision of Morpeth boards for speed reductions that didn't meet the normal criteria for advance warning to be provided. AWS was not installed at these additional Morpeth boards.

Significant speed reductions on the GWR/WR were provided with a fixed distant, which in turn meant an ATC ramp and thus a warning.

This reads as though fixed distant signals and ATC ramps were installed "in the middle of nowhere" for the sole purpose of giving advance warning of a severe speed reduction, but only speed restrictions already "under the protection of the distant signal" were so protected. The fixing of those distant signals was a recommendation made following an accident at Aylesbury in 1904.