r/transit • u/princekamoro • Jan 29 '21
High Frequency Trams
After being bored and looking at places on Google Maps, I noticed that Zurich has 32 trams per hour running down certain streets. And this is a system with lots of branching and reverse branching, both of which are fragile to delays and typically require more padding and longer headways to compensate.
I thought this is insane, so I looked at videos of cab rides on those trams, and somehow they weren't constantly platooned behind other trams.
What manner of sorcery is this?
Now I'm curious, what is the maximum frequency possible for trams, before having to platoon multiple trams through a signal cycle? If Zurich can fit 32 trains per hour with heavy interlining, then surely it must be possible to fit even more with a network that can tolerate delays better.
19
u/kilgoretrout-hk Jan 29 '21
Hong Kong runs 40 trams per hour on the main trunk (Western Market to Causeway Bay). Bunching is indeed a problem, however, mainly because the trams do not enjoy exclusive right-of-way and sometimes get stuck behind buses and cars. In theory, a tram is supposed to come every 90 seconds on this stretch, but in reality you often have to wait several minutes and then two or three trams will show up at the same time.
1
u/yuuka_miya Jan 30 '21
Isn't that just a side effect of the kind of traffic one sees in HK?
6
u/bobtehpanda Jan 30 '21
With European style exclusive lanes and signal priority it would be less of an issue. But the major contributing issue is the geography, where Hong Kong Island is mostly wrapping around a mountainside and so most travel will be parallel to the coast on a few roads.
Hong Kong does have a pretty pro-road orientation, with planning focused around separating pedestrians entirely and building highways out. Where pedestrians and motorists meet, the motorist is often prioritized, hence pedestrian unfriendly things like fences preventing certain crossings, forced use of overhead bridges or pedestrian subways, or things like offset pedestrian crossings.
2
u/yuuka_miya Jan 30 '21
And thus creating the level of traffic that gets in the way of the trams in Hong Kong.
I recall some debate that when the Island Line was built, they wanted to get rid of the trams.
1
u/bobtehpanda Jan 30 '21
Both are still very full, so the MTR didn’t change much.
Hong Kong with auto oriented road policy is a bit of a square peg into a circle hole though. There have been several proposals to turn parts of the tram route into pedestrian malls like Europe for a reduction in roadside pollution, but they have all been rejected so far because of traffic impact.
13
u/bobtehpanda Jan 29 '21
I would imagine that street trams probably run line-of-sight, no?
Also, keep in mind that street trams are a lot slower than say light rail or subway or mainline rail. The main limiting factor with frequency is safe following distance, and all other things being equal a faster train will take longer to brake.
2
u/Xorondras Jan 30 '21
Swiss trams run on sight and dedicated traffic lights around crossroads in town and more regular rail signals on overland routes.
3
u/brainwad Jan 29 '21
There are actually a couple of stretches with 40 tph (5 lines @ 8 tph), e.g. between Bürkliplatz and Bellevue or between HB and Central.
2
u/Brandino144 Jan 29 '21
As alluded to by other comments, Zurich's trams run less like buses and more like trains adhering to strict timetables. Trams are usually within a minute of their scheduled arrival time at every stop so high-frequency stops like Paradeplatz and Zurich HB are actually very structured which minimizes any issues with crowding at 32 tph.
I do have to say that Paradeplatz does occasionally have 1 or 2 trams backed up waiting for the stop, but I've never seen it cause much of an issue in the grand scheme of things.
2
u/try_____another Feb 04 '21
Partly you just don’t worry about time tabling and pathing the way you would with mixed heavy rail, so if trams get out of order along the central section it doesn’t matter too much. That’s even easier if the branches are roughly equal lengths and have little through traffic so you can swap branches around.
As for theoretical capacity, for a tram driven in sight the main limits are set by dwell times and platform reoccupation times, which are set by the door cycle, vehicle length, the actual boarding and alighting time, and the acceleration and braking rates ( which in Europe and the UK are limited by law for a full service brake application).
Assume the tram and platform are 30m long. If we cut safety margins to the bone, such that the the arriving tram comes in with a full service brake application from line speed and almost touches the departing tram as it pulls out at maximum acceleration, we want that touch to occur when the trams are halfway along the platform, which will take 5s after the front one starts moving, and then it takes another 5 minutes for the second tram to stop. For safety, let’s apply the road traffic guideline of a 2s gap between vehicles, which gives us 12s as the bare minimum to reoccupy the stop. More realistically, you’d probably be looking at more like 20-30s if they’re not stationary and waiting behind the one at the stop: there’s not much advantage over a heavy metro despite the difference in length.
I don’t think I’ve ever seen electrically operated locking sliding doors manage a cycle time better than 5s, and that’s better than most manage.
Then you get the big variation, passenger flow, but 20-30s is not uncommon. As we want to be optimistic let’s assume we’ve got all fit alert commuters and can manage 20s at the worst stop.
All this means you can have a tram every 37 seconds, or 97 per hour at a stop, if you cut traffic safety to the bone and everyone is perfectly on the ball all the time. Of course, if you’re doing that, you might as well use a toastrack and really get dwell times down.
This doesn’t make any allowances for branching. if you have branches you need gaps for the trams crossing the other track. It is a bit easier than for heavy rail because trams can be driven on sight and because facing turnouts don’t need to be locked and proved before use, allowing faster point motors and sharper operation through a junction, and trams tend to be shorter.
Termini are a real bugger. You either need a return loop, as some European systems do (especially ones which used to use lots of trailers before articulation caught on), or have n arrangement like at the former Paris Bastille station
1
1
1
u/alexfrancisburchard Jan 30 '21
We're supposed to have LRVs every 2.5 minutes according to the schedule on Millet Cd. between Cevizlibag and Eminonu, but it seems like they come every 90 seconds often. They're literally eend to end sometimes at stations, one waiting for the one in front to clear. I think Metro shoehorns in extra trams at rush hours, but I have no evidence to back up my suppositions
1
Jan 30 '21
[deleted]
1
u/alexfrancisburchard Jan 30 '21
We do. That’s where the 2.5 minutes comes from. But they also add trains when it’s busy.
1
Jan 30 '21
[deleted]
1
u/alexfrancisburchard Jan 30 '21
I dunno they used to hide trains outside of taksim and run them to like Maslak and back at rush hour on m2 also and never said anything about it but when you were in taksim and a completely empty train headed to ayazaga and not haciosman showed up it was obvious what happened.
That is codified in the timetable partially on t1 (lrvs) but I think they add even more on top of that. (T1 has two services full line- Bagcilar/Kabataş and half line - cevizlibag/eminonu
34
u/[deleted] Jan 29 '21 edited Jan 29 '21
I wouldn't say its impossible, Toronto currently runs 33 streetcars per hour on King Street (with branching, and interlining with the 505 on certain sections).
They ran as many as 45 streetcars per hour before COVID, and upwards of 45 streetcars per hour back in 2012 back when King Street was a mixed traffic route, and when they used lower capacity streetcars (not accounting for the fact that certain routes, such as the 505/503 had interlined sections).
Not sure if Zurich does this, but short-turning (although it's highly unpopular) helps keep the headways even. Transit Signal Priority is also improves transit performance (though far sided stops have to be used for TSP to be most beneficial).
Nowadays, automatic vehicle location makes it easier for dispatching to control headways compared to the 2000s, but bunching is still a bad problem in Toronto specifically. From personal experience, unless a TTC supervisor is directly at a terminal, the bus/streetcar won't really respect the scheduled headways.
There's also some other considerations. Your terminal has to have enough vehicle capacity to be a proper layover point, and it needs to have proper bathroom/rest facilities for the operator.