Radar cruise control query - don't do this at home!

[Ancient Nerd]

I am intrigued to know if anyone has experience of using radar cruise control on single carriageway roads, or has knowledge of what might happen.

The car warns that you should only use it on freeways and highways, which I assume to mean dual carriageways. This seems to be very sensible, given my experience of using it, and I have no intention of ever using it on single carriageways. However, as an academic exercise, I would really like to know how it would work in that situation.

My suspicion is that the biggest risk is from overtaking vehicles in the opposite direction, when the system might  assume a high closing distance, and do a crash stop. Or would it, given its apparent lack of awareness if another car pulls in front? Or its over-awareness when the car in front is leaving your lane. These are easy things to deal with on a dual carriageway, but might cause serious problems problems elsewhere.

Again, I have absolutely no intention of trying this, but I would just love to know.

[TheProfessor]

The caution is more about the specifications of the road, rather than the number of carriageways. Specifically, smaller roads tend to have more, and sharper, corners in them. They also have things like roundabouts, especially in the UK, and side roads/junctions. The radar has trouble tracking cars that are going round bends, turning off, etc, as the radar cone is quite narrow. Arguably, having more than one lane is an added danger, as something the radar cruise control is also not very good at is responding when a car moves in or out of your lane - it's slow to accelerate when a car moves out of the lane, and it's very fast and responds hard when a car moves into your lane, often braking somewhat harshly.

I use radar cruise control a lot when travelling on roads with speed limits at or faster than 40MPH. It works extremely well, with the exceptions being sharper bends (ones you would probably slow down to, say, 20MPH or 30MPH to go around), roundabouts, and so on. When it loses track of the car in front it'll beep and disable - be ready for and wary of the sudden acceleration/deceleration change. Also be ready to reactivate the cruise control every time you feel the need to tap on the brakes (e.g. cornering). Other than that it's great.

It's also great in stop/start traffic, traffic jams, etc, as it does all the stopping and starting (push up or tap the accelerater) for you.

[danowat]

I had a Suzuki Vitara in Iceland once that had it, worked fine on single carriageway roads (which is 99% of them!)

[QuantumFireball]

1 hour ago, Ancient Nerd said:

The car warns that you should only use it on freeways and highways, which I assume to mean dual carriageways.

In American terms, a "freeway" would be equivalent to what we call a motorway (grade-separated junctions, restricted access, etc.). A "highway" can be any major road, and not necessarily a dual carriageway.

[Heidfirst]

2 hours ago, QuantumFireball said:

A "highway" can be any major road, and not necessarily a dual carriageway.

A state highway is a bit like an A-class road here - it could be almost motorway standard but at the other end it could also be almost single track with passing places (tbh that is more likely to be a county road) ... 😛

[kithmo]

I've used it on A-roads and motorways, no problem. Just be aware that when going round bends (on A-roads), if it loses sight of the car in front, it will accelerate until it picks it up again. This can result in you taking the bend too fast for comfort. you can lessen this effect by having the cruise distance set to short (1 bar) and cutting the bends slightly, basically aiming your car at the car in front. I've not had any problem with oncoming cars and re cars cutting in front of you, it doesn't react too violently unless they really cut you up.

[thecaretaker]

I use it on A-roads that are known to be reasonably straight. On twisty country roads I want better control of the car. It works very well.

If I had to find a fault, it is if somebody turns off that the car is tracking, the car slows down OK, but when the car is no longer in front of you, it can be a few seconds before it starts to accelerates back up to speed. Not a problem for me, but the impenitent driver behind you thinks your messing about... 

[PeteB]

I love the adaptive cruise control and use it on all sorts of roads, and have learned to live with the limitations, dabbing the throttle if something is turning off in front (or when approaching a slower vehicle I'm about to overtake) and flicking the lever to cancel it when wanting gentle engine braking before a junction, roundabout, queue or whatever, then using resume.

I like the fact that on resume it accelerates very gently in ECO mode (although if a car in front is accelerating it seems to use slightly more power to try to keep up), reasonably briskly in Normal mode and very rapidly in PWR mode.

On a bendy road I will steer slightly differently (while still aiming for maximum safe positioning) to try to keep the car in front in the CC's sights, but as I'm nearly always in ECO mode the very slightly momentary acceleration if it loses its 'lock' on the car in front doesn't usually matter for the second or two before it reacquires the 'target'.

[altocumulus]

I've used the standard Toyota cruise control quite often to keep me on the straight and narrow through 30 and 40mph speed limits (especially Leeds where there seems to be a camera every 10 yards!). I've also found it very useful under average speed camera set ups.

Adaptive cruise control I had in the RAV Hybrid and used it similarly - it's just a case of getting used to and recognising the faults, especially the drop off at under 25mph, and then the magic when it tracks the car in front. And, yes, watch out it doesn't run away when going around corners faster than you might like.

In some ways I find all the TSS technology makes me concentrate rather more on driving.

I used the adaptive smart cruise control on my phev yesterday evening and nearly had a heart attack as I approached a line of traffic wondering if the damn thing was working! Luckily it was!!!!

I used the speed limiter this afternoon and found that possibly a 'better' option in built up areas, (why does the speed only set in single digit intervals instead of the cruise's 5 mph intervals?) but I'm currently on a work in progress with my new phev!

Edited September 21, 2018 by altocumulus
An extra couple of tidbits to add.

[ian rooke]

Hi trying holding the stalk down of up for 2 seconds and it should jump in 5 mph increments 

[altocumulus]

5 minutes ago, ian rooke said:

Hi trying holding the stalk down of up for 2 seconds and it should jump in 5 mph increments 

Hi Ian, I tried that because it's what one usually does with the cruise control, but it didn't respond in anything other than single steps!

[PeteB]

Hmm, what Ian says works on my 'ordinary' (non plug-in) Gen 4 Prius.  Surprised if the PiP is different in this respect.

• In Adaptive Cruise mode, flicking the stalk gives 5 mph up or down, holding it gives continuous increase/decrease in 5 mph increments.
• In Standard Cruise mode (obtained by holding the on/off button in for about 5 sec), flicking the stalk gives 1 mph up or down, holding it gives continuous increase/decrease in 1 mph increments.
• In Speed Limiter mode, flicking the stalk gives 1 mph up or down, holding it gives continuous increase/decrease in 5 mph increments.

Personally, I find these setups ideal.  My only beef is that Cruise can't be set to maintain a speed below 28 mph, and Speed Limiter can't be set below 20 mph.

 

[altocumulus]

Thanks Pete, I'll have another look - perhaps I was trying to do too much whilst negotiating traffic. It was great to see the smart adaptive cruise was active from zero without needing to be reset, very useful.

[ian rooke]

HI Pete thanks for the information about changing the adaptive cc to ordinary cc I did not know that though why I would use it like that  baffles me . 

[altocumulus]

I stand corrected.

In the RAV the flick took the current setting to the nearest 5, it didn't do the single increment. It was the same in the RAV as in the RAV hy.