cycle lanes

Is it a good idea to ride on a cycle lane? From my experience I know that if you're a professional cyclist it is not possible to cycle 100kms on a cycle lane. There are a few reasons. The first one is the condition of thm. I'm Polish and in my country cycling roads are horrible. They are dirty with lots of holes. Now I live in France and cycling lanes are better but they are only in big cities. The next reason is the speed. It is difficult to ride 30 or 40 km/h on a very narrow cycle lane. And the last reason is the number of amateur cyclists and families using them for short excursions. Cyclists are not welcome on them because it is easy to get hurt or hurt somebody. Of course if you want to ride slowly or you have just finished your workout use cycle lanes.