Roundabouts - straight lines, stability and safety
I recently had an e-mail conversation with someone about roundabout technique
as advocated by a tip on another site, and in particular about lines and
the safety aspects of straight lining them. I didn't intend to put up a tip
about this as I would hardly describe straight lining roundabouts as rocket
science - the shortest line between any two points is going to be a straight
one as any schoolboy knows - and not really what I would call advanced riding.
However, having written a detailed reply I thought I might as well make use
of the reply to explain the problems and techniques for dealing with them
efficiently and safely.
What are the basic dangers of roundabouts? All junctions where traffic flows
cross each other are potentially dangerous. Unlike traffic lights where the
flow is strictly regulated, roundabouts rely on "give way" lines and the
ability of drivers to merge into and out of the gyratory system. Like any
junction, the point of most danger is where vehicles on conflicting courses
merge and separate again - in other words where you and other drivers join
and leave the circulation round the island. Drivers foul up, they make misjudgements,
they take chances. One further danger is that cars have a big advantage over
us - they can change direction quite sharply whilst changing speed and may
perform manoeuvres that we cannot duplicate - so we always need to leave
a margin for error. Dealing with roundabouts safely calls for planned riding.
Why do we want to keep the bike upright?
What actually ARE the advantages of keeping the bike upright? You can say
that a bike is at its most stable when it is upright and travelling in a
straight line at a constant speed. But clearly this isn't of much use, because
by definition a roundabout is a place where you change speed and direction
and thus make the bike unstable by choice! Rather than simply saying that
the bike is stable when upright at a constant speed, it would be more helpful
to say that the bike becomes increasingly less stable as you approach the
extremes of use of brakes, throttle or lean angle or any combination thereof.
Thus as part of your riding plan for negotiating the roundabout, you need
to be aware that when the bike is leant over, it is hard to accelerate or
brake. Conversely, whilst we are braking or accelerating, steering and changing
line is difficult. Keeping the bike upright at a steady speed is really about
keeping your options open. This allows you to CHANGE YOUR PLAN when things
go wrong. In other words you have escape routes in an emergency.
Escape routes may include emergency braking, accelerating clear of danger
or swerving. But you can only do this if you haven't committed yourself so
far to a particular line, lean angle or speed that you have no margins. By
keeping speed down and the bike upright you can choose any of the three options
- you have a margin for error!
The Highway Code
So why are you taught to take the wide curving lines in basic training (as
in the Highway Code) if they restrict your ability to brake/accelerate/steer?
It could be argued that the Highway Code was designed for cars but in fact
the lines taught are there because they are safe, they avoid extremes of
position to the left or right keeping you out of conflict with other vehicles
in the gyratory, and importantly they giving clear unambiguous signals to
other road users about your intentions by means of your position and course.
If everyone stuck to the Highway Code system no one (including you and me)
would ever again be confused as to what someone else intends at a roundabout.
Straight lining roundabouts
We have to have a very good reason indeed for abandoning the Highway Code.
The other tip says "before we enter the roundabout we must also consider
other road users who we may come into conflict with, (in front, behind or
to the side of us.) If we would hinder any other road user's progress we
must modify our line, and thus our speed, accordingly"
Whilst I would not disagree, in my opinion this does not go far enough -
it's not simply about hindering other road users' progress - it's about maintaining
our own "safety bubble", to use police terminology. We need to maintain a
course and speed that not only sends other drivers a clear unambiguous message
about what we are doing so they can respond safely (both from their point
of view and ours) to our movements and not hopefully not "hinder" us, but
one that still allows us to deal with the mistakes that other road users
may make anyway.
So what are the potential dangers of straight lining a roundabout?
* someone may well turn right across me as I approach
* could a position tight on the left on the my approach
make a driver at the next exit think I was about to turn left and in consequence
pull out in front of me?
* could a position tight to the island in the middle of
my straightline path make the same driver at the next exit think I was about
to turn right and pull out in front of me?
* there may be a problem with the surface or traffic on
the far side of the roundabout island that I cannot see on the entry.
Each real or potential danger limits my entry speed considerably.
What then, is the advantage to me of straight lining the roundabout? I get
through on a slightly shorter line and with less steering - the bike is upright
for longer and so I have more options to accelerate, brake or steer. The
usual argument is that I can trade off this margin for error for extra speed
and get through the roundabout a second or two faster but clearly I can only
do so IF IT IS COMPLETELY SAFE - the problem is that very few roundabouts
are traffic-free, and I have to be absolutely certain in my observations.
Turning Right and Left on roundabouts
The tip goes on "If you wish to turn left or right at the roundabout then
(again assuming there is no other traffic about) you will need to maximise
the radius of the turn within the constraints of the road-layout".
The tip has a diagram showing a right turn line with a far left approach,
clipping the island and exiting close to the left hand kerb, and a left turn
line with a far right approach, clipping the inside kerb and exiting near
the centre white line.
What are the dangers of approaching a right turn from the far left? What
are the dangers of approaching a left turn from the far right? Confusing
positions expose you to the risk of YOUR approach being misunderstood by
other vehicles on or approaching the roundabout, and puts you into dangerous
positions in several different places:
* into conflict with other vehicles particularly from
vehicles overtaking on the side towards which you intend to turn - very dangerous
* extremes of position requiring pinpoint steering where
you have no room for error. Not good on the entry but worse on the exit to
the right turn where you run out of road and extremely dangerous on a left
turn where you will come into conflict with oncoming vehicles approaching
the roundabout if you run wide.
If I use a potentially confusing line, the danger is that things are much
more likely to go pearshaped! I must not take chances or make assumptions
about other road users actions. The danger of someone charging onto the roundabout
beside you is very real! Can you be 100% certain your rear observation is
good enough? Can you see over the island to be sure a car will not move onto
the roundabout from the opposite direction and turn right across your path,
forcing you to give way? If you do, you are now out of position for your
turn. How are you going to deal with a vehicle that pulls up beside you?
It's a very poor defensive line if things go wrong.
But there also a serious problem in terms of bike control - the stability
aspect we mentioned right at the beginning. The maximum radius line is less
a smooth curve than a parabola. This has a number of disadvantages:
* it forces you to keep the bike leant over for a much
longer distance through the corner
* it compromises stability
* it forces max lean angle just as you ride round the
back of the island into the path of an oncoming car that has not seen you/you
have not seen and onto a road surface you cannot see
All this means you should limit your speed (which rather negates the point
of the wide line) to maintain your margins and to allow you to swerve or
brake - the ultimate determination of safe speed is that it allows you to
stop in the distance you can see to be clear.
Ask yourself how far can you see round a roundabout on a right turn? The
answer is no distance at all - usually only a dozen metres, sometimes less!
You might be able to see a vehicle, but can you see the surface? On a typical
roundabout, there could be oil, gravel, a broken bottle or even a fallen
rider out of sight - your speed MUST allow you to take avoiding action. So
do you actually NEED to maximise the radius of the turn? Not really - your
safe speed is simply not going to be high enough to justify this extreme
approach. I cannot safely trade the wide line for extra speed. So what useful
function does maximising the radius of the turn serve? None this side of
a race track.
The Survival Skills method
So if I don't like the "wide line" approach how would I recommend you turn
left or right at a roundabout?
Firstly keeping left when you intend to turn left or right when you intend
to turn right is a "defensive" line - it is much safer to keep danger on
one side of you only and to defend your line into the corner by keeping potential
trouble AWAY from the direction you intend to turn.
After that I would recommend you follow the same sort of line I teach for
* a slower, tighter turn going deeper into the corner
will allow you to brake longer (ie more gently) in straight line, whilst
allowing a better view around the corner
* the slower mid-corner speed will allow you to stop or
steer mid-turn more easily if there is a problem when you are at max lean
* the tighter turn will have you upright quicker (ie accelerating
earlier), and thus clearing the roundabout itself faster on the exit.
* the tighter lines keep you away from the extremes of
position, giving you an increased margin for error and reducing the chances
of you running out of road on the exit .
So, keeping the bike upright longer on the entry and longer on the exit and
MINIMISING THE RADIUS OF THE TURN (rather than maximising it), keeps the
bike more stable and thus your braking/accelerating/steering options open
longer - wasn't this the main reason for straightlining the roundabout on
the straight ahead exit?? Quite simply, a slow in, cautiously round, fast
out turn is not only safer, it is also the quicker way round the roundabout
just as it is round virtually any corner on the road! For a full explanation
read Keith Code.
However fast you think you are...
...there is always someone faster. If I decide to straightline that roundabout
(or take either of the other extreme radius lines left or right) I need to
be absolutely 110% certain that no-one is going to try to outbrake me into
that roundabout. That means impeccable rear observation and not making any
assumptions about other road users.
I learned this the hard "been there, done that" way as a courier when I had
a near coming-together on a roundabout with a ZXR750 whilst following the
very straight ahead line recommended. I'd seen him miles back, he had followed
me through the previous three roundabouts and consequently I hadn't anticipated
he would try a banzai attempt to overtake on the way in to the fourth and
last in the sequence. Fortunately because I took a lifesaver glance right
before I clipped the island, I was able to swerve and we both survived but
it was a very, very near thing for both of us!
So what is safer for going ahead on an average roundabout? A slower, more
sinuous and ultimately less confusing line where drivers are less likely
to pull out, or an straight line that gives you better margins for bike control
but is more likely to force you to use those margins? I leave you to decide.
Do a risk/gain analysis for yourself.
I DO straightline roundabouts, but only when I am absolutely certain there
are no other vehicles around to be confused by what I am doing or more importantly
from my own viewpoint, to put me in any danger at all. I certainly don't
bother with turning left or right from extremes of position and using wide
Finally, think about the impression it makes on others - in my opinion, tidy
lines round roundabouts look much more professional to a watching driver
than screaming through on the racing line. Using the racing line is like
waving a red flag under an XR3i driver's nose.