Based on his name and the picture in the article, I assume the author is Dutch. We don’t have the distinction between underpasses and tunnels in our language an

Based on his name and the picture in the article, I assume the author is Dutch. We don’t have the distinction between underpasses and tunnels in our language and just call everything ‘tunnel’. It may have to do with the country being so flat that there are no mountains to tunnel through. I can only think of a single real bicycle/pedestrian tunnel, which is the Maastunnel in Rotterdam. Incidentally it is also one of the oldest tunnels in the country. It was recently renovated and is actually really pleasant to cycle through, because motorised traffic uses a separate tunnel tube. As for turns in underpasses, at complex junctions or infrastructural elements it may be tempting to just make a small bend so that the underpass is cheaper to build or easier to fit in to the environment. Take these crossroads for example: https://goo.gl/maps/21Yqj89WwyiiuZfD9 https://goo.gl/maps/21Yqj89WwyiiuZfD9. If you look closely you will see a bicycle tunnel going underneath from the southwest to the northeast. This important connection for the residents southwest of the shopping center is relatively long and has a slight bend. This makes it feel dark and unsafe to the people who use it. A better design can be found at this roundabout: https://goo.gl/maps/TXuFjXj85huufc7m6 https://goo.gl/maps/TXuFjXj85huufc7m6. Because the middle section is open, all of the individual underpasses are short and there is a lot of daylight, making cycling there safer and more pleasant.