Network rail line speeds

[BTU]

Network rail are obliged to display the lower speed via a speed board if there is a speed reduction of more than a certain amount which for the life of me I cant remember, I seem to think its either 10% lower or 20mph lower than the line speed, I know that there is no obligation if the speed changes from a lower speed to a higher speed.
Can any of you clever people remember the formula? or at least point me to the correct rule or standard for this.
Many thanks as always.

 

[hexagon789]

Network rail are obliged to display the lower speed via a speed board if there is a speed reduction of more than a certain amount which for the life of me I cant remember, I seem to think its either 10% lower or 20mph lower than the line speed, I know that there is no obligation if the speed changes from a lower speed to a higher speed.
Can any of you clever people remember the formula? or at least point me to the correct rule or standard for this.
Many thanks as always.

Do you mean a board warning of a reduction in speed? In which case I believe they are provided where maximum permissible speed reduces by at least one-third.

 

[PudseyBearHST]

Speed reduces by a third and speed is higher than 50mph

 

[Timpg]

If the speed reduces by 1/3rd or over, the speed reduction advance warning board will be supplied with an AWS magnet