As Easy As Riding A Bike)
As mentioned in my previous post, designing for cycling at junctions is important, and consequently junctions (rightly) occupy around half the length of the Cycle Traffic and the Strategic Road Network. I’ve split my coverage of junctions into two posts; this second post will look at roundabouts and ‘grade separation’, or in layman’s terms, ‘putting cycling at a different level from the road network’. That means bridges or underpasses – or a hybrid of both.
Grade separation of cycle traffic from motor traffic is the preferred solution for the crossing of all high speed road links and junctions.
Referring back to Table 2.4.2 in the document (covered in the previous post) we can see that grade separation is the only option for crossing roads with a speed limit of 60mph or higher.
It is also the ‘preferred’ type of crossings of 40mph and 50mph lanes of traffic with over 10,000 vehicles per day (or crossing two or more lanes with >6,000 vehicles per day), and for 30mph roads (or single lanes) carrying more than 8,000 vehicles per day. As mentioned in the previous post, designers ‘shall’ use the ‘preferred’ type of crossing unless other options make more sense in terms of route continuity. So clearly grade separation is important (and required) in situations with fast and/or heavy flows of motor traffic.
Naturally the two types of grade separated crossings are underpasses and bridges, although this document describes them respectively as ‘underbridges’ and ‘overbridges’, which I think is an important reframing. Good underpasses will resemble bridges, in that the cycle traffic is passing under a bridge carrying the motor traffic above it.