Why do we use overhead lines in this country, given we experience windy weather conditions? Would third rail be better?

[zwk500]

The Bay Area Rapid Transit (BART) system in California uses 1000V DC third rail and reaches speeds of 70mph (previously 80mph). I wouldn't call that low-speed.

The reduction is perhaps telling, and then there's the obvious question 'for how long do they sustain the top speed?'

 

[To the trains]

The Bay Area Rapid Transit (BART) system in California uses 1000V DC third rail and reaches speeds of 70mph (previously 80mph). I wouldn't call that low-speed.

70mph is a relatively low speed for a train. OK, 3rd rail is only used for metro systems in most countries, fixed

 

[dosxuk]

reaches speeds of 70mph (previously 80mph). I wouldn't call that low-speed.

It's slower than a Pacer.

 

[stuu]

The reduction is perhaps telling, and then there's the obvious question 'for how long do they sustain the top speed?'

BART is a bit of a hybrid system, so there's longer gaps than on the average metro. The longest is over 8 miles

 

[CarrotPie]

The reduction is perhaps telling, and then there's the obvious question 'for how long do they sustain the top speed?'

The reduction was due to excessive motor wear above 70mph and the 80mph sections being too short to deliver any real timetable benefit.

 

[Nicholas Lewis]

And of course much of the main lines from London to the South Coast would benefit from removing the restriction of 3rd rail power collection, especially the SWML.

Not sure how they would benefit given the density of traffic is surely the limiting factor so running at higher speed isn't going to help. For sure what would be beneficial would be better acceleration rates that are achieved on AC. This could be available now if there was a will to do it especially on the SW where the Desiros were software restricted initially due to the weakness of the SW traction distribution system. Subsequently parts of the system was significantly reinforced across all main routes that would have allowed a remap of the Desiro power curve but this was never undertaken. No doubt it would need a new safety case and in this world of being more energy efficient maybe not much kudos doing it. The 701's have been better optimised and may also have the ability for locational power restrictions to be automatically imposed although im not sure.

Also its perfectly feasible to provide more power in low voltage DC systems but it comes at the expense of ever increasing losses (and a lot more kit) which definitely isn't appropriate in todays environment hence high voltage AC would be todays choice.

 

[AM9]

Not sure how they would benefit given the density of traffic is surely the limiting factor so running at higher speed isn't going to help. For sure what would be beneficial would be better acceleration rates that are achieved on AC. This could be available now if there was a will to do it especially on the SW where the Desiros were software restricted initially due to the weakness of the SW traction distribution system. Subsequently parts of the system was significantly reinforced across all main routes that would have allowed a remap of the Desiro power curve but this was never undertaken. No doubt it would need a new safety case and in this world of being more energy efficient maybe not much kudos doing it. The 701's have been better optimised and may also have the ability for locational power restrictions to be automatically imposed although im not sure.

Also its perfectly feasible to provide more power in low voltage DC systems but it comes at the expense of ever increasing losses (and a lot more kit) which definitely isn't appropriate in todays environment hence high voltage AC would be todays choice.

Traffic density is always a constraint on maximum speeds where a line has a mix of fasts and intermediate services, however, the Brighton main line is four tracked to beyond where the metro services terminate, and with some careful fighting of fasts and inters, and using 387's* instead of just 377s, there could be a substantial speeding up of many of the longer journeys.
Similarly, on the SWML, the speed on the fasts from west of Wimbledon to Worting junction largely wouldn't get bogged down by the slows and most inters as each branch off the main line is grade separated. Thus the 450s* and 444s* could have the 350 motor overspeed modification to make 110mph available.
* Even if such changes were to happen, it is likely that the current stock would be replaced with contemporary EMUS a la class 730/2 Aventras as aquired for LNR services on the WCML

 

[zwk500]

Traffic density is always a constraint on maximum speeds where a line has a mix of fasts and intermediate services, however, the Brighton main line is four tracked to beyond where the metro services terminate, and with some careful fighting of fasts and inters, and using 387's* instead of just 377s, there could be a substantial speeding up of many of the longer journeys.

The two-track section of the Brighton line with Several stations and only 1 place to loop is a serious constraint on paths, although AC power might help slightly with providing a bit more oomph. Trains are already flighted pretty carefully and it drives the entire local timetable along the coasts. AC on the Brighton line would help get freight out of the way better, if 93s or 99s can be used on those trains.

Similarly, on the SWML, the speed on the fasts from west of Wimbledon to Worting junction largely wouldn't get bogged down by the slows and most inters as each branch off the main line is grade separated. Thus the 450s* and 444s* could have the 350 motor overspeed modification to make 110mph available.

Agree, the SWML west of Woking is where the biggest benefit of conversion would be faced.

 

[Nicholas Lewis]

Traffic density is always a constraint on maximum speeds where a line has a mix of fasts and intermediate services, however, the Brighton main line is four tracked to beyond where the metro services terminate, and with some careful fighting of fasts and inters, and using 387's* instead of just 377s, there could be a substantial speeding up of many of the longer journeys.
Similarly, on the SWML, the speed on the fasts from west of Wimbledon to Worting junction largely wouldn't get bogged down by the slows and most inters as each branch off the main line is grade separated. Thus the 450s* and 444s* could have the 350 motor overspeed modification to make 110mph available.
* Even if such changes were to happen, it is likely that the current stock would be replaced with contemporary EMUS a la class 730/2 Aventras as aquired for LNR services on the WCML

As i say remapping the software to use the installed power on the 444/450's would provide far more benefit than trying to get to 110mph which is perfectly feasible by the way. REP+4TC have been timed at 112mph in pre OTMDR days!!

 

[AM9]

As i say remapping the software to use the installed power on the 444/450's would provide far more benefit than trying to get to 110mph which is perfectly feasible by the way. REP+4TC have been timed at 112mph in pre OTMDR days!!

Providing a decent power supply that can be reliably collected at 110mph by suitable trains (which already exist on the UK network) would give even more benefit as well as saving energy and being safer. Running anything relying on 3rd rail at speeds over 100mph is far from 'perfectly feasible' other than as a one off test to prove that it might work. That is no way to run a continuous rail service, - it's not an enthusiast's toy.

 

[Bald Rick]

As ever - 3rd rail causes lots of issues that don‘t get reported as such.

Eg ‘signalling failure’ in the Thameslink core over the weekend and into Monday - casued by third rail traction return blowing a block joint. (You can see the newly installed joint, unwelded, at the south end of platform 2).

Broken rail the other night in Shakespeare Tunnel - caused by a third rail insulator exploding and taking the rail with it.

Something like this happens every day.

 

[Nicholas Lewis]

Providing a decent power supply that can be reliably collected at 110mph by suitable trains (which already exist on the UK network) would give even more benefit as well as saving energy and being safer. Running anything relying on 3rd rail at speeds over 100mph is far from 'perfectly feasible' other than as a one off test to prove that it might work. That is no way to run a continuous rail service, - it's not an enthusiast's toy.

Of course we all know that Herbert Walker made a poor decision 100yrs ago when he favoured third rail over the LBSCR system but it is not going to be replaced anytime, if ever, we can't even get the wires up the MML let alone finish off what GWEP screwed up. So DC is here stay and some modest schedule improvements could be made if the 444/450's were remapped to utilise more of their installed power.

 

[AM9]

Of course we all know that Herbert Walker made a poor decision 100yrs ago when he favoured third rail over the LBSCR system but it is not going to be replaced anytime, if ever, we can't even get the wires up the MML let alone finish off what GWEP screwed up. So DC is here stay and some modest schedule improvements could be made if the 444/450's were remapped to utilise more of their installed power.

Yes, that's the paralysis of 3rd rail, - minor fiddling about with it's limitations for ever higher unreliability, in the case of boosting the current available through steel rails, increasing the wasted power per passenger to boot.
My point is that the original planning and subsequent improvements to the SWML give a line eminently suitable for maximum speeds over 100mph.

 

[Nicholas Lewis]

Yes, that's the paralysis of 3rd rail, - minor fiddling about with it's limitations for ever higher unreliability, in the case of boosting the current available through steel rails, increasing the wasted power per passenger to boot.
My point is that the original planning and subsequent improvements to the SWML give a line eminently suitable for maximum speeds over 100mph.

And if they remapped the 444/450s power curve they might get close to a 100mph on a downhill section at least. This is a simple software update no other action necessary.