Started by freddyhayward, September 20, 2021, 04:39:53 AM
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Quote from: freddyhayward on September 20, 2021, 04:39:53 AMIs it intended that all railways have a height clearance of at least 2 tiles? This makes the double-height requirement for the SR-4DD meaningless.
Quote from: Sirius on October 18, 2021, 04:37:56 PMThe high-clearance-under-bridges thing seems to a bit messy anyways.Looking at busses and trams, London Tramlink flexity swifts are 3.67m tall and do not have the high clearance flag.Most modern trams are roughly 3.6m tall.Back on rails, sub-surface stock is somewhere between 3.6m to 3.7m tall depending on the exact class.The Pendolino is just 3.56m tall.DLR stock is roughly 3.5m tall.Tube stock is even just 2.9m tall.None of these can pass under low bridges, because such bridges cannot be built, except if running on unconstrainted tram tracks.
Quote from: PJMack on May 17, 2022, 01:36:09 AMI did find that when doing AC electrification of lines in Britain, several bridges had to be raised. A sixth option would be to have rail vehicles with AC centenaries be tall.
Quote from: PJMack on May 17, 2022, 01:36:09 AMI did find that when doing AC electrification of lines in Britain, several bridges had to be raised. A sixth option would be to have rail vehicles with AC centenaries be tall. (I know the clearances needed for DC overhead wires is lower than the 25kV AC wires.)
Quote from: Octavius on May 17, 2022, 01:53:27 PMThen it would make more sense not to allow building AC catenary under low bridges.
Quote from: Vladki on May 18, 2022, 09:12:02 PM- buses, and trams are IMHO easy: double deckers are tall, single deckers are not.
Quote from: Sirius on May 19, 2022, 08:52:17 PMSingle deck and double deck trams are about the same height as single deck trams got that masive pantograph tower on top.
Quote from: Vladki on May 18, 2022, 09:12:02 PMships would deserve more levels of heights, perhaps allowing for "tower bridge" that can be passed by small boats even when closed, but has to open for bigger ships.
Quote from: Sirius on May 19, 2022, 08:52:17 PMSeems overly simplified to me.I remember my recherche on Blackpool Trams.Single deck and double deck trams are about the same height as single deck trams got that masive pantograph tower on top.
Quote from: Vladki on May 21, 2022, 12:15:44 PMIf I may suggest to allow the default tallness for each road type to be defined in simuconf.tab so that other paksets may decide that some vehicles are tall by default.
Quote from: jamespetts on May 20, 2022, 11:39:03 PMThis is an interesting discussion of a complex and subtle issue. I am not convinced by the approach of requiring AC electrification to have double height tunnels, however: in reality, the difference in clearance in tunnels and bridges is relatively subtle compared to the difference in height between, for example, a Tube train and a main line train or a single or double decker 'bus, and many existing tunnels have been converted to overhead AC electrification without entirely re-boring the tunnel (e.g. the Severn Tunnel).
Quote from: jamespetts on May 20, 2022, 11:39:03 PMI would therefore suggest that, on balance, it is better to have tunnels that can be passed by double decker 'buses and trams (i.e., anything marked with is_tall=1) requiring the full height slope, and all other tunnels allowing half height. Tube tunnels would then continue to be defined by their special way constraint and this would be unchanged.
Quote from: jamespetts on May 20, 2022, 11:39:03 PMMy apologies if this involves reverting some work regarding AC electrification - but at least this will not potentially involve vast amounts of further work trying to label all AC electrified trains as is_tall=1. It also does not require any new kind of height categorisation.
Quote from: Vladki on May 18, 2022, 09:12:02 PMnarrow gauge trains also not tall
Quote from: jamespetts on May 22, 2022, 12:57:35 AMapart perhaps from some specialist double decker tram tunnels
Quote from: Vladki on May 22, 2022, 06:10:57 PMOr in some cases the old double bore tunnel was used for only one track (the clearance in the middle was enough)
QuoteDo we have any real-world examples of doubledecker tram tunnels? I expect anyone who wanted to use tram tunnels would use single deck trams. The trams would be a bit longer, but that should be no problem for trams
Quote from: jamespetts on May 22, 2022, 12:57:35 AMThirdly, as to tunnel height and electrification, this is complex. The position seems to be that (1) most main line tunnels in the UK were double bore tunnels; and (2) double bore tunnels were high enough for overhead electrification to be retrofitted without re-boring. This explains why all of the tunnels on the East Coast Main Line from London to Edinburgh, the West Coast Main Line from London to Glasgow and the Great Western/South Wales Main Line from London to Cardiff have all been electrified with overhead wires without re-boring any of the tunnels along the route. By contrast, the Woodhead Tunnels, which were originally a pair of single bore tunnels, had to be replaced with entirely new tunnels when the line was electrified with overhead DC. Similarly, when in 1976 the Great Northern and City Railway was connected to the main line and through trains run from Stevenage/Hertford to Moorgate, special dual voltage trains had to be used that would run on third rail in the single bore tunnels and overhead AC electrification at 25kV outside the tunnels, changing over at Drayton Park. There is no evidence that steam locomotives needed extra height clearance because of the smoke: the narrow Woodhead tunnels were routinely used by steam locomotives
Quote from: jamespetts on May 22, 2022, 12:57:35 AMThe "subsurface" tunnels are intended to represent cut and cover tunnels but can in fact be built underneath established buildings without disrupting them. I think that we need considerably more consistency.
Quote from: jamespetts on May 22, 2022, 12:57:35 AMIn terms of the is_tall flag, I do not think that it makes sense to have this set to 1 automatically for all rail vehicles but not for other types of vehicles, so I have reverted this.
Quote from: jamespetts on June 03, 2022, 11:23:49 AMRail vehicles are not marked as is_tall by default. Thus, ordinary rail vehicles can use cut and cover tunnels.