Overtake Prevention

[Harrier Man]

Within the first week of collecting my car, I was driving along an A road at about 60mph and following another vehicle in dynamic radar cruise control mode. The vehicle in front indicated that he intended turning right at a junction ahead. He maintained his speed until he moved into the stacking lane, I stayed on the main road. As he braked in the stacking lane, my car on the main road rapidly decelerated at an alarming rate, down from 60mph to about 20mph. Very fortunately, there was nothing behind me. Had there been, I feel pretty sure that they would have run into the back of me.

When I got home, I turned everything I could OFF, including an option called 'Overtake Prevention'. I couldn't be sure that this had been responsible because there is virtually no information in the manual about this function. However, fortunately, since turning it OFF, I haven't experienced anything similar or as frightening. 

I regard this as a SERIOUS SAFETY CONCERN in the UK. Do others agree? If so, I will raise it with Lexus. I value your opinions.

[royoftherovers]

43 minutes ago, Harrier Man said:

Within the first week of collecting my car, I was driving along an A road at about 60mph and following another vehicle in dynamic radar cruise control mode. The vehicle in front indicated that he intended turning right at a junction ahead. He maintained his speed until he moved into the stacking lane, I stayed on the main road. As he braked in the stacking lane, my car on the main road rapidly decelerated at an alarming rate, down from 60mph to about 20mph. Very fortunately, there was nothing behind me. Had there been, I feel pretty sure that they would have run into the back of me.

When I got home, I turned everything I could OFF, including an option called 'Overtake Prevention'. I couldn't be sure that this had been responsible because there is virtually no information in the manual about this function. However, fortunately, since turning it OFF, I haven't experienced anything similar or as frightening. 

I regard this as a SERIOUS SAFETY CONCERN in the UK. Do others agree? If so, I will raise it with Lexus. I value your opinions.

Malcolm, when your car decelerated of its own accord, were you aware whether or not your (brake) stop lights came on ?

[Harrier Man]

1 hour ago, royoftherovers said:

Malcolm, when your car decelerated of its own accord, were you aware whether or not your (brake) stop lights came on ?

Not specifically aware, a lot going in a very short space of time! My guess is that they would have come on because I read somewhere that if the cruise control brakes the car because, for example, somebody pulls out in front of you, then they do illuminate.

[The_Doctor]

A couple of observations

• "Overtake prevention" isn't particularly well documented in the manual and it is a bit of a misnomer, what it does it stop you going up the inside of slower moving traffic on a highway (i.e. you are in lane 1 and traffic in lane 2 is slowing down, it stops you accelerating on the inside). This to my mind fixes something I've noticed for a while as a limitation of ACC so I am all for this one.
• I have noticed on ACC it can be a bit more aggressive at slowing you down if a vehicle ahead is turning off (say in lane 1) but you want to carry on (and are in lane 2). More so than on the previous generation of ACC that I had on the ES. But as you are supposed to be fully attentive when using ACC then I simply give a little nudge on the accelerator ...
• On the brake lights, not sure of specific implemented behaviour but there is a regulatory requirement that they come on if system-initiated braking is more than a certain amount.

[Caspa]

Had similar but wasn't too concerned as was paying attention and so did the same as The_Doctor, who's hit the nail on the head as it's definitely the systems attempt to stop you undertaking a vehicle. 

 

[Al D-Much]

• "Overtake prevention" isn't particularly well documented in the manual and it is a bit of a misnomer, what it does it stop you going up the inside of slower moving traffic on a highway (i.e. you are in lane 1 and traffic in lane 2 is slowing down, it stops you accelerating on the inside). This to my mind fixes something I've noticed for a while as a limitation of ACC so I am all for this one.

I think the opposite, its a terrible piece of nanny state tech. There's no law saying lane one has to the same or slower speed than lane 2.
Stifles the flow of traffic, creating unnecessary congestion.  

 

[The_Doctor]

Well I thought there was a law about "undertaking", that's certainly the way I was brought up, but I checked the Highway Code and it is ambivalent

Rule 268
Do not overtake on the left or move to a lane on your left to overtake. In congested conditions, where adjacent lanes of traffic are moving at similar speeds, traffic in left-hand lanes may sometimes be moving faster than traffic to the right. In these conditions you may keep up with the traffic in your lane even if this means passing traffic in the lane to your right. Do not weave in and out of lanes to overtake.

I'm an engineer not a lawyer but I take it to mean in heavy congestion (like controlled motorways) you should keep up with the flow of traffic in lane, but where I have found "overtake prevention" useful is where traffic is heavy but not congested and a lane to the right starts to move slower. I don't particularly want to be barrelling up the inside of traffic and that's where I think the feature is meant to help.

[ColinBarber]

On 12/10/2022 at 12:55 PM, Harrier Man said:

Very fortunately, there was nothing behind me. Had there been, I feel pretty sure that they would have run into the back of me.

It's not uncommon for vehicles with adaptive cruise control to get confused. Plenty of vehicle forums complain about this. Certainly you don't want to follow too closely to a Tesla as they look further left and right than other vehicles, get frightened by trucks two lanes adjacent and then suffer from phantom braking.

The Lexus manuals normally have about 3 pages of warning about using the system. You need to be alert and look out for these situations where the system isn't reliable and either turn it off or be ready to press the accelerator to override the automatic braking.

[Al D-Much]

16 hours ago, The_Doctor said:

Well I thought there was a law about "undertaking", that's certainly the way I was brought up, but I checked the Highway Code and it is ambivalent

Rule 268
Do not overtake on the left or move to a lane on your left to overtake. In congested conditions, where adjacent lanes of traffic are moving at similar speeds, traffic in left-hand lanes may sometimes be moving faster than traffic to the right. In these conditions you may keep up with the traffic in your lane even if this means passing traffic in the lane to your right. Do not weave in and out of lanes to overtake.

I'm an engineer not a lawyer but I take it to mean in heavy congestion (like controlled motorways) you should keep up with the flow of traffic in lane, but where I have found "overtake prevention" useful is where traffic is heavy but not congested and a lane to the right starts to move slower. I don't particularly want to be barrelling up the inside of traffic and that's where I think the feature is meant to help.

But, you are allowed to do that as long as you don't drop into lane one undertake, then move back up to lane two. It's stated in the rule. If you drop into lane one as it's less busy or moving faster and stay in that lane you help ease congestion in lane two. 
So the computer not knowing the highway code, or being able to judge the traffic flow si going to prevent you from making a sensible choice?
That's too much "big brother" for me