Why do cycle paths always have to be bumpy? In the UK there are cycle paths laid down with proper tarmac just like the stuff they have on the roads. However, none of them that I have come across are level enough to afford a comfortable ride at speed.

I don't understand why it has to be this way, it is not as if cycle paths get dug up every five minutes like the roads do, there are no 40 tonne HGV's to break up the surface and the machines used to lay the tarmac are just like the ones they use on the road.

This is unfortunate given that most bikes do not have suspension, whereas all cars do.

What countries are there where they bother to lay cycle paths completely level? Why are the British ones never made nice and smooth? Do rough cycle paths discourage you from using them, in preference to staying on the road?

Edit:

Originally 'cycle lanes', I mean't 'cycle paths' - routes that are not necessarily adjacent to the road.
I think it is an issue of foundation mostly. Because roads get very heavy (as in weight) traffic roadbuilders spend a lot of time on the groundwork, compacting, digging away soft and unstable earth or sand layers and replacing them with gravel or other heavy rocky debris before the tarmac is laid down.

Because a bicycle path only sees light bicycles less time has to be spent stabilizing the base before the tarmac can be placed. Unfortunately this means there is less of a hard pack underneath the pavement to keep roots away, and there is not as much heavy rocks and other stuff underneath the pavement stabilizing inevitable small shifts in the ground. So bicycle paths shift a bit more, and they are more vulnerable to getting pushed up by roots.

What it comes down to -I think- is money. Building a solid foundation takes time and materials, and hence money. For a bicycle, anything paved is better than what was there before (nothing or running the gauntlet on the open road) so I assume municipalities choose to get the bicycle paths out there fast and cheap rather than roll them out slow but more expensive. Spending a lot of money on car-load resistant bicycle paths also just doesn't make economic sense for most municipalities.

The good news: Here in the Netherlands a lot of municipalities have realized over the years that the cheap bicycle paths cost a lot more in maintenance and repairs, so the quality is steadily improving.