For a change, I tried following the route signs for the station today. As well as a mystery tour near the Grafton centre where the signs simply stop, my route was blocked at Gresham Road by "WET TAR" and a sign proclaiming it. No diversion was signed and there were no advance warning signs that would have let me pick a better route earlier. Plenty of people were riding along the footways - enough that it was too crowded for me to feel safe doing so. I performed a U-turn, waited a second time at the crossroad traffic lights and rode along the very busy Gonville Place and Hills Road instead.
I've tweeted at Cambridgeshire County Council and Cambridge City Council in https://mobile.twitter.com/mjray/status/453926972843118593 because I don't think that is legal - a cycle route suddenly being blocked by wet tar does not comply with the code of practice on safety at streetworks, which is required by law. I'm disappointed to encounter this in Cambridge.