Would you?

Topics relating to Advanced Driving in cars
Pyrolol
Posts: 72
Joined: Sun Oct 04, 2015 1:52 am
Location: San Francisco

Re: Would you?

Postby Pyrolol » Mon Feb 15, 2016 12:49 am

I'd say about 380m worth of the oncoming lane (counting to more like 32 seconds at an average ~48mph - it's a bit hard to judge the end point from the video).

I like numbers: apologies to those who don't for what follows. Inevitably I've approximated a bunch of things; I think it's a pretty good model, but clearly I can't capture everything.

That means that if
- the overtake takes 2s of relative time (i.e. from a 1ish second follow to a 1ish lead from the target's perspective: pretty tight I'd say),
- you need 6 seconds to complete the overtake (commitment to safely tucked back in front; suggests 9mph/s acceleration for 2s relative: fast),
you should be able to complete the overtake without collision or course changing as long as the oncoming vehicle is doing less than 70mph.

(that's 24(6+2) = 380 - 6v: 24 being the target speed in m/s during the actual overtake portion: about 54mph)

In the video as watched, the follow is further back than that: I'd change the 2s to a 3s (needing more like 14mph/s to complete in 6s!), and only allowing the oncoming car to be doing 61mph.

Basically, from that following position, not on any day in any car. From a 1 second follow in a very fast car, perhaps. It's unhelpful that the target car is at its fastest in the most important initial stretch (unsurprising given the slope).

Astraist
Posts: 239
Joined: Thu Oct 08, 2015 10:41 pm

Re: Would you?

Postby Astraist » Mon Feb 15, 2016 8:25 am

Pyrolol wrote:from a 1ish second follow to a 1ish lead from the target's perspective[...]Basically, from that following position, not on any day in any car. From a 1 second follow in a very fast car, perhaps.


As long as we are doing numbers, those following distances are very tight.

I am not enamored with the idea of compromising following distances for an overtake. We need a surprisingly long period time to react and we also need some leeway in case of a differential in the braking capabilities of the two cars - especially in the wet.

Even as a momentary position I'd hate to be anywhere under 1.5 seconds away from another car.

Triquet
Posts: 236
Joined: Tue Sep 29, 2015 7:32 pm

Re: Would you?

Postby Triquet » Mon Feb 15, 2016 9:08 am

If driving the old Saab 2.2tid estate, my closing speed on the vehicle in front would be minimal and the available acceleration (m/sec2/blue smoke) limited, so I wouldn't bother. The prospective overtakee appears to making reasonable progress, right side of 50 mph, so I would relax and enjoy the view.

The question of course also arises with a thing like this is how well do you know the road and what overopportunities might present themselves .... :D

User avatar
jont-
Posts: 1061
Joined: Mon Sep 28, 2015 7:12 am
Location: Flatlands

Re: Would you?

Postby jont- » Mon Feb 15, 2016 9:15 am

Triquet wrote:The question of course also arises with a thing like this is how well do you know the road and what overopportunities might present themselves .... :D

Is that really that helpful though? You turn down a reasonable overtake for somewhere "better" only to find there's oncoming traffic in it when you get there.... Isn't the best plan to get past at the first safe opportunity?

User avatar
Horse
Posts: 2077
Joined: Mon Sep 28, 2015 9:20 am

Re: Would you?

Postby Horse » Mon Feb 15, 2016 10:14 am

My car? No.

My bike, possibly. Would depend on whether I knew the road (ie likely 'gotchas' of side turnings etc,) so would have already selected a 'go' gear rather than a 'follow' gear.

Would also depend on what the driver ahead had done during the previous bit of road.

That said, in slashing rain probably not :) I'd likely be following further back unless I was really keen to get past.
My own views. For better or worse :)

true blue
Posts: 54
Joined: Tue Sep 29, 2015 1:47 am

Re: Would you?

Postby true blue » Mon Feb 15, 2016 12:09 pm

The only contribution I can add is that from the start of the video you can see that any oncoming traffic would have to navigate the tightish left (for them) corner. That would give some additional margin over a flat view at distance of a corner of unknown severity that we're usually faced with.

Would I? Probably not. Would I follow, thinking to myself 'actually, that would have been on had I been in contact earlier and looking for the opportunity'? Probably.

User avatar
Horse
Posts: 2077
Joined: Mon Sep 28, 2015 9:20 am

Re: Would you?

Postby Horse » Mon Feb 15, 2016 12:48 pm

true blue wrote: Would I follow, thinking to myself 'actually, that would have been on had I been in contact earlier and looking for the opportunity'? Probably.


Doesn't negate the original decision ;) Better that way around . . .
My own views. For better or worse :)

waremark
Posts: 593
Joined: Fri Oct 02, 2015 9:23 am

Re: Would you?

Postby waremark » Mon Feb 15, 2016 4:25 pm

Pyrolol wrote:I'd say about 380m worth of the oncoming lane (counting to more like 32 seconds at an average ~48mph - it's a bit hard to judge the end point from the video).

I like numbers: apologies to those who don't for what follows. Inevitably I've approximated a bunch of things; I think it's a pretty good model, but clearly I can't capture everything.

That means that if
- the overtake takes 2s of relative time (i.e. from a 1ish second follow to a 1ish lead from the target's perspective: pretty tight I'd say),
- you need 6 seconds to complete the overtake (commitment to safely tucked back in front; suggests 9mph/s acceleration for 2s relative: fast),
you should be able to complete the overtake without collision or course changing as long as the oncoming vehicle is doing less than 70mph.

(that's 24(6+2) = 380 - 6v: 24 being the target speed in m/s during the actual overtake portion: about 54mph)

The maths is beyond me. Are you saying you overtake at only 54 mph?

Playtent
Posts: 209
Joined: Mon Sep 28, 2015 3:00 pm

Re: Would you?

Postby Playtent » Mon Feb 15, 2016 5:46 pm

Would I? Yes.

fungus
Posts: 439
Joined: Sun Dec 13, 2015 5:26 pm
Location: Dorset

Re: Would you?

Postby fungus » Mon Feb 15, 2016 9:47 pm

Maybe in good conditions, but not in that weather with standing water on the off side.


Return to “Advanced Driving - Cars”

Who is online

Users browsing this forum: No registered users and 2 guests