How long is the distance must train let when travelling behind...

[TSR :D]

... the another train? Also, can you express that distance in minutes like you would see in the train station.

 

[driver9000]

Fixed signals provide the separation so as long as the train can be stopped by a red aspect then the next train can be one section behind. The time between the trains can vary depending on section lengths, overlaps etc.

 

[michael769]

Most lines do have minimum headways expressed in terms of time.

For example the min headway though Princes St Gardens in Edinburgh is 2 minutes, West of Haymarket Station it is 3 minutes. The line towards Shotts is 8 minutes in places.

 

[ralphchadkirk]

... the another train? Also, can you express that distance in minutes like you would see in the train station.

That's called the headway. Michael's described it above so I shan't go into too much detail, but for example the headway on the Medway valley was about 12-14minutes due to the semaphore signalling along there.

 

[northwichcat]

At a train station you can sometimes see two services at the same platform at the same time with the front one departing a couple of minutes before the rear one and I don't just mean at origin stations or where portions divide.

 

[ralphchadkirk]

At a train station you can sometimes see two services at the same platform at the same time with the front one departing a couple of minutes before the rear one and I don't just mean at origin stations or where portions divide.

That's called permissive working

 

[Ze Random One]

To add to that, headways can readily be under two minutes, if that is what is required. For example, the signalling principles on many London Underground lines are not substantially different from National Rail tracks (i.e., they used fixed block colour light signalling, albeit with different technologies and working practices). These lines can comfortably achieve a train every 2 minutes or so.

Most NR Commuter lines have a "planning headway" of around 3-4 minutes, which is the rule followed when designing the timetable. It should be noted that the "planning headway" is designed to leave a little room for manouvre, as trains can be easily delayed by a few seconds here or there.

I should also note that a 3 minute planning headway can mean a wide range of distance separations between trains.
If two 40mph trains are planned to be 3 minutes apart, they will (at line speed) be 2 miles apart
If two 100mph trains are planned to be 3 minutes apart, they will be 5 miles apart.
So you can see that time separation and distance separation are two distinct things, and a slow train can follow another much closer (by distance) than a fast one.

 

[156402]

That's called the headway. Michael's described it above so I shan't go into too much detail, but for example the headway on the Medway valley was about 12-14minutes due to the semaphore signalling along there.

Medway Valley is majority of Absolute Block (AB) working so 'headways' don't exist in terms of planning. With AB you can't depart a station until 2 minutes after the train in front of you has cleared the block section ahead. The only sections of the MV that have headways are Paddock Wood to Wateringbury and Cuxton to Strood, which I believe both are 7 minutes.
--- old post above --- --- new post below ---

To add to that, headways can readily be under two minutes, if that is what is required. For example, the signalling principles on many London Underground lines are not substantially different from National Rail tracks (i.e., they used fixed block colour light signalling, albeit with different technologies and working practices). These lines can comfortably achieve a train every 2 minutes or so.

Most NR Commuter lines have a "planning headway" of around 3-4 minutes, which is the rule followed when designing the timetable. It should be noted that the "planning headway" is designed to leave a little room for manouvre, as trains can be easily delayed by a few seconds here or there.

I should also note that a 3 minute planning headway can mean a wide range of distance separations between trains.
If two 40mph trains are planned to be 3 minutes apart, they will (at line speed) be 2 miles apart
If two 100mph trains are planned to be 3 minutes apart, they will be 5 miles apart.
So you can see that time separation and distance separation are two distinct things, and a slow train can follow another much closer (by distance) than a fast one.

All planning rules for Network Rail can be found on their website!

 

[ralphchadkirk]

Medway Valley is majority of Absolute Block (AB) working so 'headways' don't exist in terms of planning. With AB you can't depart a station until 2 minutes after the train in front of you has cleared the block section ahead.

That is the headway. I quote RoTP:

AB indicates locations where absolute block signalling applies: here the headway is to be calculated from the transit time of the first of each pair of trains running between the consecutive block posts being considered.

Therefore headway = SRT + 2

 

[The Planner]

Yes, but seeing as it is based on the SRT it is always stipulated as AB otherwise you would have a myriad of headways.

 

[156402]

Yes, but seeing as it is based on the SRT it is always stipulated as AB otherwise you would have a myriad of headways.

Have to say NR don't make it easy, in terms of the Medway Valley, mandortary timing points are Paddock Wood, Maidstone West, Cuxton and Strood. However, there are many intermediate block sections which make planning a train difficult on that route.

In contrast, Peterborough to Leicester, all block sections are mandortary timing points and is fairly straight forward!

 

[The Planner]

That has only recently happened on Peterborough to Leicester, a few of the boxes were never timed at as it didn't require it. Ketton and Whissendine have only been used in the last couple of years, Luffham and Ashwell are very recent. The Medway Valley is likely to be the same.

 

[Southern]

Out of interest, does anyone know the headway on the Maidstone East line? It's just that whenever trains from the coast are diverted that way, only 1tph ever runs between Ashford - Charing Cross.

 

[156402]

Out of interest, does anyone know the headway on the Maidstone East line? It's just that whenever trains from the coast are diverted that way, only 1tph ever runs between Ashford - Charing Cross.

Its 4 minutes but the reason only 1 tph is due to crewing issue's (the bigger picture is taken rather than one depot). Remember engineering works generally use more train crew than a base plan!