The M25 has always seemed to suffer from a ripple effect - hold ups which suddenly appear then disappear for no apparent reason.
I've hear it is due to the combination of high volumes of traffic and the erratic braking of some drivers. If this is so, why havn't I ever come across the ripple effect on other busy motorways ?
Have I missed something or is the M25 a special case for some reason ?
Any ideas anyone ?
|
Ever tried the M3 between 4:30 and 7:00 on any week night? Likewise the M27 eastbound from J1 every weekday morning. The ripple effect can be seen on most motorways at peak times and does seem to be caused by poor lane discipline, excessive braking and an inability to allow traffic to join from sliproads.
Admittedly, the M25 does seem to excel at this..... Good thing I rarely venture that way these days!
No Dosh (no idea)
|
|
|
Ripple effect occurs on all motorways.
I *think* it might be more frequent on the M25 becasue the variable speed limits give drivers one more thing to brake for.
--
These are my own opinions, and not necessarily those of all Toads.
|
|
|
SWMBO was naggin me on Friday pm and I wasn't paying 100% attention to the road ahead and found myself braking late (and harder than necessary). Looked in the rear view mirror and could see the start of a ripple effect going off into the distance.
The problem is that I believe a mile long jam can take 5 mins to create but 15 mins to clear so by the time you get to one of these (I believe called) phantom jams the original problem has long gone.
|
The "ripple effect" is the result of queuing theory. As a system with a finite capacity (speed limits and 3 lanes) gets more heavily loaded, then bunching occurs as each slowdown brings traffic together and speed limits prevent it stretcjhing out again..
The effect can also be seen at the start from traffic lights...
Usually capacity usage> 65% or so causes the problem. Since most motorways are carrying twice the design load...
madf
|
|
You don't sound mad at all :-)
|
There was a TV programme about this a few months ago. It filmed the M5 at holiday time from a helicopter. All it took was one vehicle to brake sharply and the ripple effect spread a long way back.
That was on just one lane. However that was the cue for drivers in the slowing lane to swap to a lane that was moving ok. That caused someone in that lane to brake and .......
|
A chap called William Beaty has written a good set of webpages on this every subject: www.eskimo.com/~billb/amateur/traffic/trafexp.html He calls the effect traffic wave theory.
teabelly
|
Teabelly
Without reading the whole of this article, isn't he advocating exactly the same principle as the M25 variable speed limits - i.e. getting everyone moving at teh same (slower) speed gives better progress than stop/start
|
|
|
|
|
I think the M25 suffers more than most because of the number of junctions in close proximity, and the fact that it gets a bigger share of the short hop users, on at one junction and off at the next.
|
|
|
That's why there are the variable speed limits on the SW section of the M25. By easing everyone's speed there is less differential so less braking and reduced ripple effect. I understand that it works well.
PB.
|
|
|
volvoman
I can tell you its very very true, on the bike i'm not as affected as car drivers are, I can go through it. And there is nothing there except traffic. I understand that the maximum carrying capacity of a motorway is at 18 miles per hour if distances are kept for speeds etc. I can do 15 mph more than this safetly through the jams.
Bill
|
|
Also it's noticeable how the ripple effect occurs more on the outside lane than the other two lanes. There must be a reason for this, but one reason has to be the lane hogs in lane 2 which leave lane 1 comparatively empty and force people into lane 3 where tialgating inevitably occurs.
|
|
|
|
