'Dew on train tracks blamed for delays'

[mumrar]

Damp road, damp wheels don't stop my car, damp runway damp wheels don't stop airlines. Damp rails, damp wheels trains stuffed. Any part of that statement you can't cope with?

So your car can stop in an emergency under heavy braking when it's cold and the road and wheels are damp just as quickly as when it's warm and dry?

Was physics a subject you didn't pay much attention to at school? Trains typically run upwards of 100tonnes, with metal wheels and metal rails as a point of contact. If you add water into the equation (you know what they are, right?) then you get a practically frictionless scenario where adhesive weight counts for a lot less than when it is warm and dry.

 

[TDK]

Another issue with modern trains is the switch from tread brakes to disk brakes. Tread brakes keep the wheel clean and tend to rough it up a little, so improving adheasion, wheras disk brakes to not. I don't really get the obsession with disks on everything these days, especially on EMUs with rheostatic/regenerative braking where the brakes are only being used at low speed (where tread brakes are more effective than disks). Even worse when on a lot of modern trains the disks are far noisier than any tread brakes. Disks are only needed for high speeds, although even the TGV and Eurostars use tread brakes on the powercars, which can be used from top speed.

Disc brakes are far superior than tread brakes from high speed and you cannot rely on the Rheo/regen brakes not failing at some point if i remember correctly if the regen fails the train still needs to stop within it's stopping distance for the line speed you do get quite a bit of brake fade even from 70mph on a tread braked train

 

[O L Leigh]

The other thing is that the regen/rheo brakes tend to be isolated during the autumn on at least some classes of unit because it only acts on a certain number of wheelsets rather than all of them, making the trains more vulnerable to sliding.

O L Leigh