30k speed limits for all urban areas on the way

yeah, back on topic; i'm going to do a little calculation and this might be a bit wordy but i am laying out my calculations in the hope that if i've made a mistake, someone can spot it.

the usual example i use of driving in urban traffic is DCU to UCD or vice versa. it's approx 11km, and currently google maps is estimating 31 minutes to drive it. that's an average speed - on a summer saturday afternoon - of 22km/h. most roads used have a speed limit of 50km/h (with the stretch between UCD and donnybrook at 60km/h IIRC), so cars are reaching less than half the average speed that the speed limits would allow.

let's say the car could only do 50km/h or zero. no inbetween speeds. that implies that the car would spend 13 minutes moving and 18 stopped (it takes 13 minutes to drive 11km at 50km/h). it'd take 9 minutes longer if the car was limited to 30km/h instead of 50km/h (and this may not be accurate - that is based on an the assumption that the time spent *stopped* would be the same)

based on that, we've a theoretical max difference of nine minutes. and that's a *maximum* - in reality, the difference would be a lot less because a lot of the time spent moving would be well under 50km/h anyway. and it's also worth pointing out that (AFAIK!) most of the roads used in that particular example will remain at 50km/h anyway.

add heavy traffic, and the difference will shrink even further.

or, TL;DR - if you were only allowed drive at 30km/h instead of 50km/h, it'd cost you a theoretical *max* of 8 minutes for every 10km you drive. you'd drive clear across dublin in less than 20km (the M1/M50 roundabout to leopardstown racecourse is 19km)

yeah, it's not going to be policed. however, the sort of person who would do, say 60km/h in a 50 zone might end up doing 45 in a 30 zone, even without policing. i've noticed this where i grew up, when visiting my parents - they introduced a 30km/h limit on delwood road in blanchardstown and while people are still breaking the limit, the average speed you see cars doing on the road (in my experience) is noticeably reduced.

a reduction of 60 to 45 is a 44% reduction in kinetic energy of the vehicle - with a similar reduction in braking distances, etc.

those chicanes have been there for many years; if you go back to the 2009 imagery on street view, they're there - just in case anyone reading your post assumed they were introduced along with the 30km/h limit.

'cyclists are a different class of road users with differing sets of laws applying' is not the same as 'cyclists can run reds'. My 6 year old niece doesn't have trouble with that level of logic.