we used to have toilets on the tube, but the IRA kept on sticking bombs in them.
the "troubles" were utterly destructive, and left permanent scars in the UK. However it nothing to the sheer destruction that occurred in NI/6 counties.
The Financial Times only recently(~2010) began receiving post at their HQ because the amount of suspicious shit that used to mailed to them and other press outlets. All of the glass was laminated, so that should a lorry bomb be detonated there, it wouldn't shred everyone behind them.
for the UK, terrorism was always something to do with the troubles all the way up until well past the iraq war. London was neutral ground, much to the annoyance of the rest of the five eyes.
In the UK we call it Northern Ireland, in some/most parts of Ireland its called "the 6 counties".
 I only have a limited frame of reference here
Northern Ireland is far from a third world Country, don't believe everything you see on TV, come up and visit us and see for yourself :)
Hah, if that isn't the perfect illustration of the folly selecting your data to support your argument.
No doubt N Ireland is lovely. Dublin is too. A lot of people of the world be thrilled at the opportunity to live in either place.
And I'm sure both have worse parts, since every sizable settlement needs a less desirable part to concentrate it's less desired residents.
This artery has multiple splinter-off points after a point, but there is a choke point where if things go bad you have no choice but to wait or fight for your chance of which escape into the wider//bigger world of roads you want.
I'm not sure why I noticed this whilst I live here yet I did.
Perhaps reading "Deep Survival: Who Lives, Who Dies, and Why" had something to do with it.
The "defensive design" things like bollards and big planters that block walkways are like rung 1 (or 0.2, perhaps) on the "defensive earthworks" ladder. Its a well studied field and there's counter-actions available for most of that kind of thing. An attack may become more expensive to prepare and require more resources in flight but the bollards and defenses can be hit first and removed.
Judging by the results off all the upgraded security measures since 9/11; we can see what is actually feared.
I'm not sure what tractable measures they could take (that's not my job to figure out and if it was I wouldn't do it for free) but I feel very confident saying that whoever or whatever group next takes a swing at government will likely do so outside of whatever measures protect the workplace.
However I would kindly direct you to specify which grade of steel you are thinking doesn't behave like this. Especially as the steel used in pre-stressed concrete is very different from the steel used in aviation.