My local council has implemented two different types of cycle lane. Both involve narrowing the main carriageway. One raises the pavement, puts the bike lane at a slightly lower level, then the main carriageway at a lower level still, with a sloped kerbs so cyclists wanting to turn right across the carriageway can do so. The other type involves having the usual pavement on one side of the road, then the main carriageway, then a double-width, bidirectional bike lane (slightly raised), then a usual width pavement.
I am very much in favour of the former type, where there's a pavement and cycle lane on both sides of the road. It seems to be a natural evolution of the existing bike lanes. I used to cycle the same roads these lanes are going on, and I can see the advantage. But as a motorist, I do find the road narrowing to be somewhat annoying, especially as it removes the flexibility to get around broken down vehicles and buses at stops - especially now the bus stops have all been filled in!
I don't think the double-width lane layout is at all practical. It is great for segregating cyclists away from the main carriageway, but likely it's a real pain in the backside for the cyclists. First they need to deal with other cyclists riding towards them in a narrow space. Then, if they need to cross both lanes of the carriageway to get to a side road, that could involve crossing the other side of the bike lane first, then both lanes of the carriageway.
On one stretch of road with this layout, the double-width bike lane switches from one side of the road to the other. Cyclists are expected to dismount, cross the road at a designated crossing, then resume cycling on the other side. I am sure that for some cyclists, they will do this. Especially family groups where speed is not a priority. However I wouldn't be surprised if accidents involving faster cyclists who prefer to cycle on the road go up in this area - I can see cyclists preferring to stay in the main carriageway, then drivers overtaking them. And as the carriageway is so much narrower than it used to be, they will not have as much space to do so. It will only be a matter of time before a motorist tries to overtake a cyclist and screws it up, hitting the cyclist.
As a motorist though, I know it will annoy the hell out of me when I end up following a cyclist down a narrowed main road doing 15mph when there's an empty cycle lane RIGHT THERE!