Interesting sub-thread popping up - thought it might benefit from being split out.
Some of the recent comments:
sussex2 wrote:Mr Cholmondeley-Warner wrote:Ralge wrote:I have always taken a blind spot check in lane changing or joining a carriageway as being a 90-degree sideways glance as a belt-and-braces check before committing to the move.
DTES' take on it is quite clear as is Roadcraft's:
"Always check that no-one is sitting in your blind spot before you change lanes. Make sure you know where the offside and near side blind spots are on any vehicle that you drive ..." Page 61 of this year's edition.
So I would still advocate a check that goes no further than 90-degrees but one that turns your peripheral vision into the danger zone.
I think I tend to want slightly more than 90 degrees. The Boxster, especially with the hardtop on, has a huge blind spot behind the driver, such that it's only possible to check up to 90 degrees. I find myself feeling very vulnerable in being unable to check those last few degrees. Rational thinking, and testing with overtaking cars, shows that vehicles are visible earlier in the mirrors than I thought they were, but I still hanker after a proper check, by looking directly.
As we all know, the purpose of shoulder checks is to verify that you haven't missed something from other observation, principally the mirrors. Once you've been used to checking, going back to mirrors alone feels less safe. Discouraging people from checking seems to me to be on a dangerous course towards relying on one source of information only.
My feeling is with the quote from the 2007 edition that proper use of mirrors should be enough. I certainly do not generally make an over shoulder check when joining motorways or dual carriageways.
However this does depend on the situation including the vehicle I am driving so I would not be dogmatic about it
I think changing lanes and joining are a bit different. Quite often I don't feel the need for a shoulder check before changing lanes. Usually I've already been monitoring what's happening behind in my mirrors, and unless there's somewhere a vehicle could have come from that I wouldn't have seen, there isn't anything to look for.
When joining though, I check over my shoulder much more often, and it is over my shoulder - I think I rotate my head more than 90 degrees and I'm looking back up the carriageway behind me. There's one obivous difference compared to changing lanes in that there's clearly no way I can have been previously monitoring what's going on behind. But also, when changing lane there is just the traditional blind spot, between what the rear view mirror and wing mirror can see, whereas on a slip road, until quite late you are probably not quite parallel to the carriageway and laterally further from it, and the mirrors aren't much use at all. If the layout is amenable, I don't want to wait until I'm in the final part of the slip road where the broken line starts before starting to try and find out what's happening behind me, and so looking with my eyes instead of the mirrors is often the only option.
Mind you, being laterally further from the carriageway, the pillars themselves can provide pretty good blind spots when you turn your head too. I had an entire Audi A6 estate - a new, fat, huge one - hide in my B pillar blind spot when I looked over my shoulder yesterday morning. And (not that it's got anything to do with looking behind you) I've also had the A pillar hide a car ahead in lane 1 before.