The mutual impact of the vehicles gradually increases with the decrease of the freedom of the vehicles operation in high-density traffic flow.

在高密度交通流状态下，车辆行驶的自由度下降，相互影响逐渐增大，主要以跟驰行驶和换车道行驶为主。

youdao

To put it another way, what would be the accident rate on London's A-roads if you filled them with Northumberland's density of traffic?

BBC: Crashes

In July and August, the population density and traffic becomes so thick with vacationing Romans that one can push their car across the capital, Portoferraio, at about the same pace as driving it.

BBC: Following Napoleon��s trail on Elba

How do we know if the road type is swamping any effect from traffic density?

BBC: Crashes