Unidirectional vs Bidirectional

General discussion of passenger rail proposals and systems not otherwise covered in the specific forums in this category, including high speed rail.

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dowlingm
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Re: Unidirectional vs Bidirectional

Post by dowlingm » Tue Aug 05, 2014 7:46 am

Myrtone wrote:Yes, but the TC lines have a wider minimum curve radius and a lesser ruling gradient than the legacy system. Many big European unidirectional networks (most using pantographs, some with 750v) don't have as many problems as Toronto, they have plenty of intermediate turnbacks, or use triangular junctions for shortworking. They either have small bidirectional fleets, or couple unidirectional trams back-to-back when a line is templorarily truncated.
If the loop system is such a pain, why are you still buying unidirectional rolling stock rather than switching to bidirectional running?
Because sometimes you have the system you have, and I don't run the TTC... I did point out the capacity advantage of unidirectional but bidirectional would have made uprating the capacity of the Union Station streetcar terminal a bit less invasive and costly than it's going to be.

I do think we should have regauged the 512 St Clair line to 1435mm when it was rebuilt and joined it to the uptown network, but unfortunately the Eglinton project and the yard to go with it wasn't ready to roll.

Myrtone
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Re: Unidirectional vs Bidirectional

Post by Myrtone » Tue Aug 05, 2014 8:18 am

I didn't notice that you pointed out the capacity advantages of unidirectional running. According to an entry on Steve Munro's blog, Transit City was originally going to be TTC gauge, but then changed it to standard gauge.
talltim wrote: But if the issue was clearance between tracks then it wouldn't work with bidirectional trams, trams on one track would have the body shifted away from the other track and the ones on the other track would have the body shifted toward the first track and you would end up with exactly the same (lack of) clearance as you started with
Could you have bidirectional vehicles with the body shifted to one side? Yes, why bother with (hugely) asymmetrical vehicles designed for bidirectional running? Then again, why bother shifting the body if the track centres are adequately wide? This would shift the centre of mass towards the wheels on the kerbside, with uneven axle loads.
Your Immagination is fine but I do hope it is tempered with a healthy dose of symmetry when it comes to bidirectional vehicles.
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dowlingm
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Re: Unidirectional vs Bidirectional

Post by dowlingm » Tue Aug 05, 2014 9:42 am

Metrolinx (who will operate the uptown lines) required the uptown LRVs to be more in keeping with the sort of lines being constructed as new build as they will own them rather than the TTC. The same LRV order will equip Kitchener-Waterloo's ION line, and likely Mississauga's LRT as well.

The reality is that TTC likely has as much economy of scale as it's going to get since the 204 downtown car order plus the additional 60 the TTC CEO is looking for is massive when you compared it to most North American light rail setups.

Given that Bombardier was the only serious player to bid on the downtown order (100% low floor, tight curve radii, single point switches, trolley pole had to be supported during transition, 2.54m width rather than the common 2.4m and 2.6m yadda yadda), and now they have the additional advantage of a car which will have operated in service, it would be understandable if Metrolinx was also fearing a vendor lock-in scenario should they have gone with a similar car on the notion that one day the systems would be unified.

Myrtone
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Re: Unidirectional vs Bidirectional

Post by Myrtone » Wed Aug 06, 2014 2:16 am

dowlingm wrote:Given that Bombardier was the only serious player to bid on the downtown order (100% low floor, tight curve radii, single point switches, trolley pole had to be supported during transition, 2.54m width rather than the common 2.4m and 2.6m yadda yadda), and now they have the additional advantage of a car which will have operated in service, it would be understandable if Metrolinx was also fearing a vendor lock-in scenario should they have gone with a similar car on the notion that one day the systems would be unified.
I recall that Siemens did bid, but left the bidding process due to unfair treatment. Skoda and Inekon could have bidded (see superior plus, but the TTC was unfair.

Will the current Bombardier low floor order be the last new LRVs the legacy system will ever need? Trams can last over 50 years in routine serivce, as happened here in Melbourne with the W class, and Adelaide with the H class, and in Milan with the Peter Witts.
It has puzzled me that even the newest points on the legacy systems when nearly all other tram systems in the developed world, newbuild or legacy, use double bladed points. In Melbourne, we used to have plenty of single bladed points, but they're nearly all gone now.
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talltim
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Re: Unidirectional vs Bidirectional

Post by talltim » Wed Aug 06, 2014 4:54 am

Myrtone wrote:I didn't notice that you pointed out the capacity advantages of unidirectional running. According to an entry on Steve Munro's blog, Transit City was originally going to be TTC gauge, but then changed it to standard gauge.
talltim wrote: But if the issue was clearance between tracks then it wouldn't work with bidirectional trams, trams on one track would have the body shifted away from the other track and the ones on the other track would have the body shifted toward the first track and you would end up with exactly the same (lack of) clearance as you started with
Could you have bidirectional vehicles with the body shifted to one side? Yes, why bother with (hugely) asymmetrical vehicles designed for bidirectional running? Then again, why bother shifting the body if the track centres are adequately wide? This would shift the centre of mass towards the wheels on the kerbside, with uneven axle loads.
Your Immagination is fine but I do hope it is tempered with a healthy dose of symmetry when it comes to bidirectional vehicles.
Well, the original example did have insufficient track centres for the width of vehicle they wanted, and they did built asymmetrical ( unbalanced?) vehicles for it. http://www.railroad.net/forums/viewtopi ... 15#p860081" onclick="window.open(this.href);return false;
If you can build asymmetrical vehicles with one cab, then you can build them with two. However, unless they turn rather than reverse at the ends of their journeys, you lose any advantage you gain in clearances.
Tim David

dowlingm
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Re: Unidirectional vs Bidirectional

Post by dowlingm » Wed Aug 06, 2014 11:47 am

The current Toronto ALRV fleet is being retired first because the electronics are too hard to source and too expensive to replace with something newer - given some other fleet issues it looks like they will be stripped to keep their CLRV cousins going until 2024. I think it's fair to say that newer LRVs will have shorter average lives than the likes of PCCs unless there is a transformation in modularisation to ensure new generations of electronics can be cost-effectively introduced.

As to the RFP process... I don't think many people looked at what went on there without a criticism. Different people might have different criticisms though!

Myrtone
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Re: Unidirectional vs Bidirectional

Post by Myrtone » Sat Aug 09, 2014 1:54 am

Like most legacy tramway networks, especially in Europe, Gothenburg is looped unidirectional, all their trams having doors on only the right, but there is one underground section in Hammarkullen, right under a mountain, there is one stop there which does have a center island platform. Trams on this section use the tunnel on the left, crossing over just south of that stop. Obviously an island platform would make sense here because the station presumable can only be accessed from above and staircases and elevators can be shared between platforms, rather than duplicated or placed on only one side.
So even with driver controls at one end and doors on only one side, either side or center platforms can be used, depending on running directionality. Then again, a a single-sided tram might not be able to dwell at stops on the wrong side but could still run one lines with such stops.

EDIT: Gothenburg does also run coupled unidirectional trams.
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