I live in Swansea but used to work in Port Talbot - a 12mile cycle each way which I did most days for many years. It is not the most scenic route, much of which is right next to the dual carriageway. Many times have I been soaked by lorries or busses thundering past in bad weather. Nowadays, this main road is reduced to 40mph which seems really slow when you are on it, but bit by bit the motorists are slowing down and keeping to the limit. I am sure this is much safer and healthier for the cyclists (of which there are many due to the new University).
My cycling time was 40 minutes +/_ 5 minutes irrespective of what time I left. Car time was 25mins min - up to 50 mins max depending on traffic and the time I left the house. Also sometimes when taking the car, I would often deliberately leave early or stay later at work to avoid the traffic..... so bit by bit the case for cycling starts to make sense.
The soul destroying traffic is down to the traffic lights of which there are many ( I think my journey in the car would include 20 sets of lights
) and sheer volume of cars (95% with one person in) - but not the reduced speed limits.
When I wasn't cycling, I would take the car and generally be part of the rush hour, I would leave the house later than I should have and then invariably find myself in the outside lane "champing at the bit" because the car in front wasn't getting out of the way, accelerating into the gaps etc. etc. I would regularly pass one of my engineers pootling along in the inside lane (doing the speed limit) - but he would always pull into our works carpark a minute or so after me.
The last bit of my journey to work involved a fairly clear road which you could vent your frustrations after all the "nose to tail" driving and speed up a bit....... however this was actually a 30mph limit and the local constabulary eventually twigged that they could nick a few unsuspecting drivers (particularly those who had left the house late...). And so it was.
Several of my fellow directors were nicked for doing well over the 30 limit - not sure what the rules are on this but apart from the 3 points on the old licence and increased insurance - they all got landed with a hefty fine based upon their salary. Unfortunately some had just had a bonus which was included in the calculations - end result was a fine in excess of £2000
I do find the 50mph limits on the M4 more tedious than the new 20mph limits BUT everyone sticks to the limit because of the cameras, and I definitely get better mpg as a result. So I am slowly buying into the whole idea, even the 20mph limits (although I am probably doing an indicated 25mph).
I think we need to give the 20mph more time to see how it pans out. Electric bikes provide a fantastic way to get cars off the road and lower speed limits will surely help this - because they will not be building loads of cycle paths overnight. A recent visit to the Netherlands and Belgium showed me just how bad the UK is on the integrated travel. They are MILES ahead of us.
A footnote to this is that cycling to work improved my fitness immeasurably... I had a saying that each day I cycled I would save 4 1/2 pounds. That is £4 in petrol and 1/2 pound in weight.
Sadly, these days my cycling has stopped, and my weight is inexorably heading "north"