Can bad infrastructure be to blame for accidents?

[Vierwielen]

While some sort of barrier may well be required...

It's this that I'm unclear about. Why is a barrier needed at all?

In normal operation, I presume the tram runs along the tracks through the junction, including stopping at both the signal-controlled junction and the tram stop. Just now while the work is going on, there are no trams running through the junction, but evidently they stop fairly close to where the planter is. In any tram system there is always a small risk of mechanical failure, driver illness or deliberate mischief by a driver or passenger that could lead to the tram failing to stop where it should and putting people at risk.

During normal operation (without the planter or roadworks), there is a small chance of something going wrong that makes the tram disobey a stop signal and hit vehicles or pedestrians crossing the junction on green. If it's going fast enough, it may derail and hit the stop shelter or other road users. During the closure, without the planter there, there's a similar small risk of the same thing happening. So my questions are these:

1. Why is the small risk associated with a tram hitting the workforce at the stop considered to be more worthy of mitigation than the same risk of the tram running a stop light and hitting traffic?

2. Why it is considered acceptable to mitigate this small risk - for small it must be not to warrant any mitigation under normal operation - by restricting visibility to road-borne users of the junction (not just cars and cyclists, but pedestrians as well)?

As I say, I must be missing something here, because these questions really shouldn't be beyond someone whose job is to ensure safety on a tram system.

It appears that trams have a dead man's handle which greatly reduces the risk of runaway trams. Also, the main difference between the operation of trams and trains is that the tram driver is required to ensure that the track is clear before using it whereas a train driver reads the signals to check whether or not the track is clear and safety is designed accordingly.

There is of course a risk that the tram driver might be contemplating a spectactula suicide, but how is that different to a bus driver or an HGV driver having similar tendencies?

[FosseWay]

it's not like restricted visibility signal controlled junctions are unusual.

True, but there are two fundamental differences between the junction with the planter and the one you linked to (and countless others, as you say).

1. At the junction you linked to, there is the width of the pavement to account for. When a driver proceeding on green can see along the pavement of the road they're crossing, they can see any errant red light jumpers, and the RLJs can see the person with priority. At typical crossing speeds, that makes a difference. On the video, there's no wiggle room to the right of the driver or the left of the cyclist. I suspect that if the cyclist had jumped the red from the left and not from behind the planter, both parties would have seen each other quicker. Also, if Ashley Neal's analysis of the cyclist's error is correct, and he didn't deliberately run the red, he might have had some positive corroboration of the actual state of the lights - red for him - if he'd been able to see the traffic moving off from his left, which he couldn't with the planter there.

2. This may not apply to people not used to driving on the left, but basically anyone used to driving in the UK will naturally tend to presume that in any given circumstance they have more visibility to their right than to their left at a junction. On most normal light-controlled roads, you've got the whole of the other side of the road as a buffer against red light jumpers and errant pedestrians, which at sensible junction speeds should give both you and the other party time to react. We know innately that we don't have the same buffer zone to the left, so our attention naturally gravitates there more than to the right, at least at first: we look at the point where risks are most likely to arise most quickly. So the motorist may not even have been looking towards where the cyclist came from (not that, in this case, it probably would have made much difference).

If you then artificially restrict the view from the right, you are introducing a non-normal state of affairs. Yes, sure, drivers should react to that in various ways, but they're human. In a roadworks situation like that, they will have all sorts of other non-normal calls on their attention as well, such as closed roads or narrow lanes. It's the job of the TM people on site to minimise unnecessary distractions so that the drivers can focus on the unavoidable ones.

[Big L]

I’m not sure why the “buffers” in
this view couldn’t have been moved, say, 5-10m towards where the tram is sat. Still functional, much better visibility.

[KeithW]

It's this that I'm unclear about. Why is a barrier needed at all?

In normal operation, I presume the tram runs along the tracks through the junction, including stopping at both the signal-controlled junction and the tram stop. Just now while the work is going on, there are no trams running through the junction, but evidently they stop fairly close to where the planter is. In any tram system there is always a small risk of mechanical failure, driver illness or deliberate mischief by a driver or passenger that could lead to the tram failing to stop where it should and putting people at risk.

During normal operation (without the planter or roadworks), there is a small chance of something going wrong that makes the tram disobey a stop signal and hit vehicles or pedestrians crossing the junction on green. If it's going fast enough, it may derail and hit the stop shelter or other road users. During the closure, without the planter there, there's a similar small risk of the same thing happening. So my questions are these:

1. Why is the small risk associated with a tram hitting the workforce at the stop considered to be more worthy of mitigation than the same risk of the tram running a stop light and hitting traffic?

2. Why it is considered acceptable to mitigate this small risk - for small it must be not to warrant any mitigation under normal operation - by restricting visibility to road-borne users of the junction (not just cars and cyclists, but pedestrians as well)?

Well the first thing to remember is that a tram has steel wheels running on steel rails , there is much less adhesion so braking distances are longer. Trams are also typically rather heavier than buses. I did a check and it see the Edinburgh trams weigh 56 tons and have a top speed of 70km/h. Thats a lot of kinetic energy.

Then there is the reality that drivers are human and can just get it horribly wrong as happened in Croydon. The reality is tragic as it is if a pedestrian steps in front of one you will not get a mass casualty event but if the tram goes through the buffers all bets are off. I believe the system is being extended so I would be surprised if the planter is not a temporary solution, indeed a look at GSV suggests that is indeed the case.

https://www.google.com/maps/place/Hideo ... -3.1681726

[jnty]

I’m not sure why the “buffers” in
this view couldn’t have been moved, say, 5-10m towards where the tram is sat. Still functional, much better visibility.

Suspect there needed to be room for two full sets in the turnback section to allow a set being rescued by another set to turn around, or to "dump" a broken down set at the buffers end while still allowing normal turnback operations to continue while it's there.

In any case those buffers are now gone.

I note the bollards there with interest. I wonder if could be a perceived vehicle incursion risk we're not appreciating that the bollards, and subsequently the big wooden thing, are designed to provide protection against.

[Glen]

I’m not sure why the “buffers” in
this view couldn’t have been moved, say, 5-10m towards where the tram is sat. Still functional, much better visibility.

That buffer stop has been permanently removed so the new track could be constructed. It's not that one which is creating a visibility issue, it's the temporary measure, which has to be large enough to be held in place solely by its own weight.

[KeithW]

I’m not sure why the “buffers” in
this view couldn’t have been moved, say, 5-10m towards where the tram is sat. Still functional, much better visibility.

That buffer stop has been permanently removed so the new track could be constructed. It's not that one which is creating a visibility issue, it's the temporary measure, which has to be large enough to be held in place solely by its own weight.

Clearly that is the reason for its choice but I dont see why the temporary buffer has to be so large as to block sight paths through the crossing, the previous buffer was by definition temporary as it is no more.

[AndyB]

Clearly that is the reason for its choice but I dont see why the temporary buffer has to be so large as to block sight paths through the crossing, the previous buffer was by definition temporary as it is no more.

The previous buffer was permanent in the same way as permanent traffic lights which have been replaced. Permanent buffer stops as Glen refers to are fixed to the track, but the temporary buffer is not.

The answer is that you may be right and something smaller might have been just as effective, but Glen might be right and nothing smaller which could withstand a particular collision force was available - and the engineers know the answer to that question.

[FosseWay]

Clearly that is the reason for its choice but I dont see why the temporary buffer has to be so large as to block sight paths through the crossing, the previous buffer was by definition temporary as it is no more.

The previous buffer was permanent in the same way as permanent traffic lights which have been replaced. Permanent buffer stops as Glen refers to are fixed to the track, but the temporary buffer is not.

The answer is that you may be right and something smaller might have been just as effective, but Glen might be right and nothing smaller which could withstand a particular collision force was available - and the engineers know the answer to that question.

That's only half of the story, though. Risk consists of two elements: severity and likelihood. The ability of a given obstacle to withstand a given amount of force applied to it is only relevant to the severity side of risk. It says nothing about the likelihood of a tram hitting it in the first place, nor about the relative likelihood of that happening vs. an entirely foreseeable RTA occurring as a result of restricted visibility.

[AndyB]

There is probably a minimum standard spec for a temporary stop block for use on running lines, rather than sidings which have different requirements.