Explained: High performance movement limiting devices

Take a deeper dive into what defines a high performance movement limiting device, the approval criteria, and the risks associated with not using one.

Our first blog looked at what being ‘Network Rail approved’ means and the processes behind it. This second blog focuses on high performance movement limiting devices (MLD), exploring what they are and the requirements needed to obtain approval.

First off, what does high performance mean?
A high performance movement limiting device is permitted to work much closer to open rail lines than a low performance device. High performance devices allow for work up to 300mm from the rail running edge, where as low performance is up to 3000mm from the rail running edge.

They must be designed so that there is no credible single point failure that would cause the system to fail to an unsafe condition. The GKD Series 3 (and the previous 3RCI model) use dual verification, which monitors two sets of sensors and compares the data it receives to look for faults, failures and anomalies.

What are the other requirements of a high performance device?

  • It will be designed so that a failure of any component or system relating to speed management will cause the system to revert to the slower speed.
  • No part of the machine will fail under fatigue loading for the foreseeable life of the machine as a result of the foreseeable loads imparted by the limiting device.
  • Electronically controlled movement limiting devices will allow the safe recovery of the vehicle to within the pre-set limit.
  • It will be capable of demonstrating that the machine cannot go beyond a pre-set limit when lifting the maximum permitted load on the most adverse cant and gradient.
  • The system should know the orientation and position of the chassis relative to the track / line open to traffic.

What are the control measures for safe working when operating over 3000mm from the nearest open line rail running edge?
The COP0032 Issue 3 code of practice document states that:

The use of plant that has a High Performance MLD fitted should always be preferred. Where High Performance MLDs are not fitted, it is acceptable to use a Low Performance MLD as long as they have worked correctly during the test and there is no cause to question their reliability. If MLDs are fitted they should be set up to the planned limit of work and be active. other methods should also be implemented (e.g. wall, barrier, train, tunnel, demarcation etc).

What are the control measures for safe working when operating less than 3000mm from the nearest open line rail running edge?
The above distance also includes working on station platforms. The code of practice document states that:

The plant must be fitted with a High Performance MLD which must be configured and functioning correctly, where relevant a load stabilisation method is in place that is able to reliably prevent the load from swinging towards the open line.
There is another method for ensuring that the item of plant and any load cannot physically foul the open line (e.g. train, tunnels, wall, or barrier which is capable of withstanding foreseeable forces exerted during operation) and that the method used can be demonstrated to reliably prevent the plant and load from fouling.

Hopefully that now explains a bit more about what a high performance movement limiting device is. Use the links below to go back to our first blog on Network Rail approval and to check out our Series 3 safety system for road rail vehicles.

Discover more

GKD Series 3

Discover the Series 3 safety system for RRV's and MEWPs

Explained: The network rail approval process

We explain what exactly obtaining 'Network Rail approval' is, the process that it takes to gain it, and which GKD safety systems are Network Rail approved.