Dudley Horscroft wrote:
> Given the length of a train, it could be pan

> down at the front while feeding power from the rear, then pan up at the front while the rear pan is off the wire. Or perhaps the

> pan does not even need to come down - the wire could just go up, stop then start again the other side.

>

Depends on if QR pans have height limiters, which since there are no
other 'air gaps' on the system, they probably don't.

There were 'air gaps' on one of the US systems where the wire just
gently rose and stopped, then after a gap came down on the other side -
they were phase breaks.

The Dutch have done similar over opening canal bridges - to avoid the
complexity of overhead on a lifting bridge, the wire just stops and the
trains coast over bridge.

But if the pantograph isn't specially equipped, it will raise too high
and either topple over under it's own weight or immediately 'flip' when
it hits the incoming wire on the other side. The height it rises to has
to be constrained to something nears it's normal operating height.

I don't see why QR would bother though - if the height of the overhead
is a risk to air traffic, wouldn't the train itself be also considered a
risk ?. What's the height of the contact wire above the train ?. 1m to
1.5m ?