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Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 8:30 am
by AndrewBurns
Hey all, I very nearly had an accident yesterday when riding home and it was definitely my fault.

I was riding down a long relatively shallow hill in a suburban area on my commuting bike (about 13kg, disk brakes, 28mm slick road tyres) coming up towards a roundabout. The speed limit on this road is 50 kph and due to the shallow hill I was riding I could easily hold ~45 kph along the road and so I was in the middle of the lane just as any other vehicle would be. I'm always concious of the possibility of a car entering the roundabout from my right so I was watching it like a hawk but because of houses and trees there's almost no visability to the right. Everything was clear until I was about 20m from the roundabout and then suddenly a car appeared with very little warning because of the lack of visibility. I pulled on my brakes hard, sat back over the rear of the seat to stop from going over the bars and got to the point where my rear wheel was lifting off the ground and locking and only just slowed down enough that the car made it through the roundabout before I arrived. Unfortunately there were two cars coming from the right and there was no way that I could stop dead before reaching the roundabout, luckily the other driver saw the situation I was in and slowed down to allow me to pass through the roundabout ahead of him but if he'd kept driving I would have run into him.

So my question is, what do people do in this situation? I was travelling well under the speed limit, I was very attentive and on the brakes as hard as I could be as soon as I saw another vehicle coming from the right but the bicycle simply can't slow down as fast as a car. I could of course go slower but then I risk attracting the wrath of other impatient road users and how slow is slow enough? I think part of the problem is also road design, this roundabout is probably fine for a car that can stop much faster than me but in my case the speed limit was too high for the amount of visability I had. Unfortunately there's not much that can be done about that but it does raise an interesting point, I'm sure roads and speed limits are already designed with stopping distances and visability in mind, perhaps some thought should be put into the visability a bicycle would need during the planning stage?

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 8:41 am
by il padrone
Ride slower, brake earlier. It is your responsibility to always travel within your ability to stop, given your sight distance. A speed limit is not a goal, approaching a roundabout 30kmh is probably more than enough. 45 on a bike is over the odds.

Following drivers must stay behind or overtake safely. If they get aggro, wave and blow kisses.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 8:47 am
by RonK
Are you serious? It's up to you to approach intersections and roundabouts at an appropriate speed so you can stop if necessary.

The speed limit is exactly that - the maximum speed at which you are permitted to travel, not the safe speed for any particular vehicle.

Slow down.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 8:55 am
by Strawburger
Hi Andrew,

A few points:

I'm pretty sure there is a road rule based around bicycle speed approaching an intersection. You are probably going too fast.

Is this a local roundabout? Let me know the location and I'll go check it out, I am happy to help out a club/forum member!

All designs perform stopping sight (vehicle distance to stop), approach sight distance (view of the intersection linemarking) plus one for safe intersection sight distance (view to other vehicles). If this is an old intersection it may need revisiting however a bicycle should be able to stop in a shorter distance and have a more favorable viewing perspective than a car driver (unless it's a recumbent).

It's a balancing act to be fluent with the sydney traffic. My advice is don't worry about what the car drivers think of you. They will let you know in a verbal or hand gesture sometimes but it's way better than being at fault ploughing through another vehicle or save a motorist an extra 2 seconds so they can get to the next traffic light faster!

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 8:59 am
by rkelsen
Use this as a learning experience. Thank your lucky stars that it didn't end badly and maybe approach intersections a bit more cautiously in future.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:28 am
by sogood
All roundabouts are to be approached as for a give way sign ie. Ready and able to stop on the line. Rider's and driver's responsibility.

This case brings out an interesting issue that has bugged me for a long time. The fact that currently cyclists are not required to learn road rules before getting on the road, the chance of mishaps are bound to increase, especially now more and more young inner city residents are bypassing their DL and living the green life. Further, the lack of motor vehicle driving experience, they have no ideas on the limitations of driving a motor vehicle and are more likely to put themselves in harm's way. Time has changed.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:33 am
by il padrone
I don't reckon travelling at a speed prepared to stop is a matter of testing. It's more a matter of common courtesy and self-preservation. Plenty of drivers, who have done the test, manage to lose sight of this requirement.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:35 am
by sogood
NB. This is not meant to be a debate on licence for cyclist though it likely will lead to it. Putting that aside, I think there's good ground to ensure cyclists going on the road are well versed in basic road rules.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:39 am
by RonK
sogood wrote:I think there's good ground to ensure cyclists going on the road are well versed in basic road rules.

Quite so.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:39 am
by sogood
.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:43 am
by il padrone
sogood wrote:Putting that aside, I think there's good ground to ensure cyclists going on the road are well versed in basic road rules.

+1

Just suggesting that it takes more than just our inadequate driver licencing system. Safe cycling demands longer-term training (on-road) and a shift in rider attitudes.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:45 am
by il padrone
[deleted]

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 9:46 am
by sogood
.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 10:26 am
by AndrewBurns
Yeah for sure I understand that I was going too fast and I was lucky, not debating that. And I am a driver too, full license have been driving for years to and from work around the area and I suppose I'm just more used to how I would approach an intersection like that in a car compared to a bicycle.

Here's street-view of the roundabout: https://maps.google.com.au/maps?hl=en&l ... 76,,0,3.55

As you can see there's a high fence and lots of greenery to the right so you can first see the oncoming cars as they enter the roundabout. I'd say the maximum safe speed I could approach this intersection on my bike is more like 25-30 kph.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 10:38 am
by sogood
Such a common suburban roundabout layout. Nothing difficult. Just need to slow down and be prepared to stop at every roundabout per road rule. Nothing to do with sight line.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 10:41 am
by il padrone
AndrewBurns wrote: I'd say the maximum safe speed I could approach this intersection on my bike is more like 25-30 kph.

Yes, I'd say that'd be about right. I go through a roundabout just like this one near my home, maybe slightly better sight distance. Mostly I cruise along the flat road at 25-30 kmh so I don't have a huge braking issue.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 10:44 am
by Cheesewheel
Pursue Stavra segments with roundabouts at your own peril ...

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 10:55 am
by Strawburger
Yeah, I have ridden that one a few times, usually turning into or out of wattle. The grade of the road is downhill coming into hermitage from wattle, and hermitage is also on a downhill heading toward Vic road. 20-30 km/hr is more suitable. I think the road has recently been resurfaced and rolls a lot smoother too.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 11:06 am
by herzog
Bikes don't stop as well as cars for many reasons:

High C of G
Small contact patch
High tyre pressures
No suspension
Lower mechanical advantage of brakes


We all have to allow for this in our riding.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 11:34 am
by zero
AndrewBurns wrote:
So my question is, what do people do in this situation? I was travelling well under the speed limit, I was very attentive and on the brakes as hard as I could be as soon as I saw another vehicle coming from the right but the bicycle simply can't slow down as fast as a car. I could of course go slower but then I risk attracting the wrath of other impatient road users and how slow is slow enough? I think part of the problem is also road design, this roundabout is probably fine for a car that can stop much faster than me but in my case the speed limit was too high for the amount of visability I had. Unfortunately there's not much that can be done about that but it does raise an interesting point, I'm sure roads and speed limits are already designed with stopping distances and visability in mind, perhaps some thought should be put into the visability a bicycle would need during the planning stage?


Motorists can't typically negotiate the roundabout faster than you. ie if you are slowing to 30 for vision reasons on approach, they are generally slowing to 30 because of the chicane effect.

If you know you want to slow, and you know you have a car behind you, stick your hand up and signal with a stopping signal before braking - along with some extravagant pantomime of looking this generally gives the impression of what you are doing. I do this occasionally when I want to brake for an obscured possibility rather than a visible danger.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 11:56 am
by human909
While I'm sure I can dig up a road rule to show that your behaviour was foolish. I think it can all come under the common sense rule of:

DON'T ENDANGER YOURSELF BY GOING TOO FAST!


(I think you also need to question your driving skills if you routinely approach roundabouts at high speed! :shock:)

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 12:38 pm
by tubby74
sogood wrote:All roundabouts are to be approached as for a give way sign ie. Ready and able to stop on the line. Rider's and driver's responsibility.



This is a problem with current driver training. With even professional instructors tauting the "give way to the right" rule drivers (and many cyclists) take the approach that they won't slow down until they see that they really have to, and often then it's too late. Plenty of small suburban roundabouts have limited line of sight on the approaches,and if you are still doing 40-50 there's every chance a car will get ont he roundabout before you, hence they have right of way, and you cannot stop.

The lack of sight seems to be designed in to many places expecting to slow drivers down but it just doesn't work. Rumble strips could help in some places but you really wouldn't want them outside your house.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 12:43 pm
by il padrone
Australian road authorities design roundabouts poorly, focusing on high vehicular speeds :roll:

In contrast to some European urban roundabout designs that focus on protecting vulnerable road users and slowing the vehicular speeds.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 1:20 pm
by sogood
il padrone wrote:In contrast to some European urban roundabout designs that focus on protecting vulnerable road users and slowing the vehicular speeds.

Even those aren't impediments to cycling speed. Just bunny hop! Watching hours and hours of TdF late at night aren't wasted.

Re: Bicycle stopping distance and road design

Posted: Wed Jan 16, 2013 1:25 pm
by herzog
I think he was probably referring to the common European design where each throat of the roundabout contains a zebra crossing.