If they arrive simultaneously both travelling at the same speed and/or take off from rest then they are not on a collision course, they can both go, they have to be separated by some distance, there should be absolutely no problem here!
If they both enter simultaneously and one is starting from rest and the other, for arguments sakes enters at 60km/h then they will be on a collision course, the vehicle that is travelling too fast will be deemed to be at fault....approaching the rounabout at a speed where it can not avoid other traffic already on the roundabout they have to enter at a speed so they can stop if someone does enter just before them on the left or at the same time.
They only have right of way if they enter first, but if they were going at excess speed they can still be held responsible.
Most roundabouts have signs telling drivers to either slow down or a suggested speed, in suburban streets where roundabouts are tight and small drivers are also logically expected to drop from the 50km/h as they enter, not see how fast they can get through it. Regardles, motorists are obliged to approach them at a speed so they can avoid a collison if there is the simultaneous entry.
Commsirac
Can't agree with your entirely. Look at my description of this particular roundabout again. I stated that traffic travelling from the freeway has a 70kph speed limit applying. There is absolutely no sign warning to slow down for the roundabout, only a roundabout warning sign, which is interpreted quite differently. Common sense says "roundabout coming up, slow down". Unfortunately, slowing down means coming back from more than 70 because the traffic has just exited from a 110 kph freeway and is generally still travelling at between 80 and 90 kph. Slowing down under those circumstances is interpreted as coming down to the 70 kph speed limit.
The roundabout I described is a large one, dual lanes entering from east and west, witht he 70 kph limit applying in both directions. It's located on a major off-road for a freeway and feeds heavy traffic during all times of the day into a large percentage of the region where I reside. As I stated, vision for the traffic entering from my street is limited. If oncoming traffic on your right is travelling at 70 or thereabouts, you have very little time to see the car, estimate its speed and enter the roundabout
legally, having arrived at the roundabout first, with absolute safety
The vehicle travelling at speed may well be deemed to be at fault because they entered the roundabout
after the vehicle on their left, but they would still have been travelling within the speed limit. Of course, that would be of no consolation to you if you had just been T-boned by a car on your right travelling at 60 or 70kph - you would probably be past caring.
It's my opinion that this particular roundabout needs additional traffic controls, such as a reduced speed zone on the eastern and western approaches, and improved line of sight for the side road traffic to see oncoming vehicles on their right. As I said earlier, somebody will surely die at this intersection before much longer. Maybe then, something will be done about it.