Neil Williams wrote:

On Tue, 11 Jan 2005 10:47:21 +0000 (UTC), "Terry Harper"
wrote:

Really the answer is to provide an extra lane between junctions, so that
there is never any need to merge off a slip road.

I don't like that when driving a slower vehicle (e.g. a minibus)
because it means you are forever moving back and forth.

Only if you stick to the extra lane.

I think most
lorry drivers would probably agree - unless such lanes were
permanently marked with dotted lines to be for turning vehicles only.

They do a similar thing on the A2 between Falconwood and Dartford. The
leftmost lane was designated "local traffic only" and apart from buses,
all vehicles in it had to leave at the next junction. The rules were
relaxed slightly when they found that traffic wasn't always able to
merge, and the roundabouts near the Danson Underpass could not cope with
the traffic volume, so some people were driving the wrong way down a one
way street in order to avoid the jams. The lane is still "local traffic
only" but it no longer all has to leave at the next exit.

The solution is just to have a slip road such that the
slowest-accelerating vehicle you're likely to get on a motorway (say,
an oldish, heavily-laden lorry) can accelerate safely to the
prevailing speed of the inside lane (let's say 60mph or so) without
going absolutely flat out.

There is no single solution - different locations have different
constraints.

That would probably, I'd say, involve doubling the length of a good
proportion of existing sliproads with an upwards slope to motorway
level (the downward ones obviously assisting with acceleration), and
tripling the length of all sliproads which have a give way just before
the motorway is met (such as older services stations). Planning the
merge would also be easier with a longer period alongside the motorway
itself.

To merge traffic safely on the motorway, drivers (even of slower
vehicles) shouldn't need to be slamming through their gears attempting
to accelerate to the prevailing speed when they should be already
thinking about the actual merge.

Even with a decent length to do it, merging can be a problem.