A (probably) silly question: What causes traffic jams on motorways?

[Xt500]

“The faster the vehicles are travelling then the more vehicles the road can carry” will only work if the space between each vehicle is correct. If everyone drove correctly, such that the distance between vehicles increased appropriately with increasing speed, then there wouldn’t be hold ups unless the road reached saturation. The problems come with some people leaving inadequate space, having to suddenly brake, and causing the concertina effect. A blanket 40 or 50 limit during busy periods allows more traffic than the 70 limit only because it keeps everyone at a similar speed, takes away any desire or opportunity to overtake, accelerate into a gap etc. There is less likelihood of anyone making the sort of sudden change that initiates the concertina. So traffic does not stop/start.

 

People keep banging on about gaps but its well known to them that look out of their vehicle windows that the faster drivers drive at the more they increase the gaps.Look behind any old codger and they are like they are making a close coupled train,yet when the speed goes up so do the gaps.