SCE wrote:
Quote:
SCE said "If traffic is light, then no problem with HGV overtaking in 3rd lane of 4 lane motorway as long as not likely to cause obstruction." - but if traffic was light, they would not need to use lane 3.
Fair point, but what if HGVs in lane 1 doing 40, being overtaken by HGVs in lane 2 doing 45, and HGV pulling empty trailer doing 56 comes along. If he can overtake in lane 3 without causing obstruction then i would have no problem with it. May be unlikely but not sure driver in lane 3 should be at risk of prosecution for taking opportunity to overtake in this situation, as long as his manoeuvre is carried out safely and with consideration.
OK, let's consider your scenario. In lane 1 we have A doing 40mph. Behind him, we have B doing 45mph, and an HGV pulling an empty trailer which we will identify as C.
The scenario begins with B in lane 2, but assuming traffic was light which is what we said to begin with, one assumes that B began in lane 1, some distance behind A. He's about to pull out to overtake in lane 2, but C is coming up behind at 56mph. With heavy vehicles, maintaining the momentum is important. So if I was driver of B, I think I would wait for C to go past, rather than forcing him into lane 3 - even if usage of lane 3 was still legally available for HGV. If each of the vehicles was 40ft in length, the tail of C would be 80ft behind the front of the cab of B at the moment C's cab draws level with B's tail. C is travelling 11mph faster than B, and 11mph = 16.13ft/sec. If those speeds were maintained, it would take C only a fraction under 5 seconds to pull clear of B. In reality, B might slow to 42mph in anticipation of being overtaken by C, in which case the speed differential would be 14mph = 20.53ft/sec. Now, it would take C less than 4 seconds to overhaul B. So B's sacrifice in speed would be very small, and only very brief - much better, in my opinion, than having HGV spread out over ¾ of the motorway.
But let us suppose that B does decide to go ahead and overtake A, while C is coming up behind in Lane 2. It would take about 11 secs for B to overhaul A, but let's round this up to allow for a gap between the vehicles. (We know that HGV don't maintain the 1yd/1mph rule of thumb
) Let's say it takes 15 seconds in total. C is gaining on B at 11mph = 16.13ft/sec. In the 15 seconds it takes B to overhaul A, C would have closed the gap with B by about 242ft. Assuming that each driver likes to keep a reasonable amount of space in front and behind, then even if C were only 100 yards behind B at the time B pulls into lane 2 to overtake A, B could complete the overtaking manoeuvre and be back in lane 1 without C having to slow down at all.
As you can see, requiring HGV to use only lanes 1 and 2 would be a small price to pay to improve overall motorway throughput, and is a price worth paying to avoid seeing HGV side by side occupying lanes 1, 2 and 3 at 45mph - a daily occurrence on motorways like the M25 through Surrey.
<edit @ 17:33 on 15/12> - speed difference between C and B is 11mph, not 9mph in my earlier figures. I have made the necessary corrections.