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.

Roundabout Basics

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 the roundabout.
    * 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 all corners.

    * 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 angle
    * 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 lines.

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.