The M3 Jct 2 -4 a went through a 4-lane and smart upgrade in recent years, the project completing in June 2017.

I've been commuting it since Sep 2017. The increased capacity and smart features generally keep the traffic moving, usually around 60 mph upto J2 M25, with no restriction onwards to A316 Chertsey Rd.

However....

My experience of regularly driving northbound leads me to take the view that the design has introduced a serious collision blackspot - namely, the J2 northbound exit onto the M25 anti-clockwise, towards Gatwick.

This exit is served solely by Lane 3 - one in from the outside lane. J2 exit Lanes 1 & 2 are M25 clockwise only. Its a common occurrence for M25 anti-clockwise delays to result in slow traffic on Lane 3 of M3, bunching up far sooner than the other 3 lanes.

The smart signage does control speed limit to mitigate this, but it doesnt make clear that there is slow/stationary traffic in Lane 3 only.

Furthemore, drivers with less familiarity of the rather unnatural layour of J2 exit, who are trying to get onto the M25 anti-cw, don't get themselves into lane soon enough, or take Lane 2, realise their mistake, and dive late into L3.

Even furthermore, L3 is dual purpose - exit to M25 anti-cw AND through lane staying on M3. The more cautious driver intending to stay on the M3 can get bunched into exiting anti-cw M25 traffic, and then try to nip out into the often much faster L4, outside lane.

The lane signage for this lopsided exit jct begins at 2 miles out. Its as clear as it can be, but my personal belief is that many drivers unfamiliar with it either dont fully comprehend it, or are being misled by sat navs that arent up to date with the layout.

In summary, the M3 J2 northbound exit design makes L3 a 'concertina' lane, causing bad collisions. This month I've seen the aftermath of 3 collisions, one of which was a 6 vehicle nose-to-tail concertina, that I witnessed first hand. It was caused by traffic slowing suddenly in Lane 3, as cars joined late from Lane 2 to exit towards Gatwick. At least three of the vehicles looked write offs.

This morning was another 2 vehicle collision in the same spot.

The police must be escalating this. It can't go on.