How about the traffic blocks on the bus travel at day time?
There are no frequent roadblocks on either of the Buses routes, shuttles, taxis or the private vehicles in the day- except for situations where the need arises. Transport in city of london has been well strategized and works in a timely order. Which means, if there is a road block, it's possibly a short one that might have resulted from an accident or fair disobedience to road practices. And is soon cleared up in a couple of minutes.
if there are definitely going to be a road closure, then it’s certain it would be brought to general notice and followed up with more reasonable options. In london, road closures are mostly likely possible within the day and even the night. It does not only affect the buses, (if there are any on the route), but affects every other medium of tour on the route.
Some possible causes roadblocks or closes are
Spontaneous Road Accidents
On highways and Sophisticated roads likewise -- Anything can happen at anytime. Accidents of different types occurs more like in every other city in the world so it's not that special here in london. And when this occurs, chances are that the section of the road will remain closed for a period of time until the process is been evaluated and cleared (which normally takes less than 30 minutes or thereabouts, depending on the severity).
Repair or Construction works
If a serious government environmental restructuring or construction works is going on the highway, then there are chances a second option has to be figured out. Routes can be interrupted at one end, depending on the gravity of the project at hand. Information would also be disseminated on the occurrence.