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Sometimes I am approaching a red light from 1/4 mile+ away at 50mph+. Cant always time the light and cant just drive 30mph "in case I will need to stop". Assume at least one vehicle stopped at light in each lane ahead of you?

If I am not sure when the light will turn green, how should I manage my decelleration?

A. Just balance assist/regen to 0 and "glide"? I may still be coming in too hot to the light then.

B. Let regen just max out to slow me more, even using S gear to bleed off speed.

C. Other ideas

Thanks,
Carl

If your odds of making it are better than your odds of missing it, I recommend giding (no assist, no regen, no fuel). If your odds of hitting it read are higher you might want to let off the throttle to let it regen but you honestly won't gain all that much energy. I'd probably stick with a glide until I see it start to turn.

I agree with Tim


In my case, many of the lights I deal with vary in duration depending on the day of the week, time of the day and traffic conditions; which makes it very frustrating trying to predict and plan ahead.

But, my preferred approach is to always assume I will come to a stop, yet I slow down slowly (foot lightly off gas) in hopes that the light will turn green before I get to it. If the likelihood of a stop is greater then I may as well get as much regen as possible. Gliding all the way to the intersection may force me to call for an aggressive stop when I realize that the light will remain red a little longer and that is a worse waste of energy. In the other hand the rate of regen depends on the amount of room ahead of me.

It is a fun game isn't it ?


MSantos

Thats what got me thinking....

Coming in HOT but then getting a green means you are not wasting momentum - but the odds of the green are smaller since time to the light is shorter....

Decellerating more (with regen) wastes some momentum - but the odds of the green are greater since time to the light is now longer....

What I was thinking was maybe something in between, like EARLY max out regen for a short time to take you from say 50+ to <30mph then glide for as much of the distance as possible and wait for the green.

I assume that actually coming to a stop in this case is worst option for FE?

This is Prius-specific as far as I know, but I'll capture more total energy by "normally" braking (a deceleration rate around 2 MPH/s) than I would by using the "fake drag" regen where my foot isn't on either pedal. So, if I know something about the light, such as "it's unlikely it's going to turn in the next 15 seconds, some slowing down will be needed", what I'll probably do is something like your last suggestion:

What I was thinking was maybe something in between, like EARLY max out regen for a short time to take you from say 50+ to <30mph then glide for as much of the distance as possible and wait for the green.

- More cars waiting for the light = more initial slowing down.
- Something that clues you in that it might be a longer wait (e.g. left turners waiting in the opposite direction and you know there is a protected left) = more initial slowing down.

I assume that actually coming to a stop in this case is worst option for FE?

Yes. If you can preserve any momentum at all it's better than completely stopping.

I like to use a combination of my minimum speed and the distance to the next car in front of me as a metric for how well I executed a situation like this. Higher minimum speed is of course better, but if there's still a big buffer in front of me when I hit that minimum speed (and everyone else starts pulling away again) I know I could've done it better.

Edit: I like these real-world "How would YOU do it" questions. Forum sub-topic? Regular series?

Thanks Locutus

- I also hate to gamble on a green coming soon and run up on waiting vehicles (destroying the buffer) since I usually then get pinched from ahead and behinnd and start driving stupid (with everyone else).

- Today was a special one. Route 23S between Columbus and Circleville doing 54mph I see a Red with a few semis in rt lane and a few cars (that passed me) in the left. I did slow early but then thought about keeping speed and passing the semis. Instead, I continued to slow with max regen to <15mph right behind the last semi. Luckily, got a ~15 mile draft (all at 55 :)) from that semi after that, so maybe this was best in this situation.

C. Other ideas

Thanks,
Carl

FAS. Maybe its different with a M5 Insight but sounds like a perfect opportunity. Especially if you have kept the pack up you won't recover as much energy as you save by shutting it off NOW (IMHO). And then brake some to keep it moving when the light turns green, and then bump start it.
Gary

I thought he was talking about an HCHII. But lately in my MT Insight I've been coming in foot off the gas, ICE-ON, in a fairly high gear for less engine braking (depends on the speed, but generally 4th). As I understand it, the Insight has DFCO (decel fuel cutoff) so no fuel will be used under these conditions, and regen braking will capture at least some of the kinetic energy. Depending on the situation I may downshift to 3rd or directly to 2nd once I slow down further to reap a bit more regen. If I want to save a bit of momentum I will push the clutch in and may shift to neutral.

FAS. Maybe its different with a M5 Insight but sounds like a perfect opportunity. Especially if you have kept the pack up you won't recover as much energy as you save by shutting it off NOW (IMHO). And then brake some to keep it moving when the light turns green, and then bump start it.
Gary

Yep, probably applies to HCH2 as well - good idea!

Not much rolling resistance in FAS so you might have to brake some from 50+mph.

I probably would not use FAS if my pack was down at 5 bars or less - or I will probably get into forced regen once I startup/accelerate. Probably would not FAS unless traffic pretty light behind me.

Yep, probably applies to HCH2 as well - good idea!

Not much rolling resistance in FAS so you might have to brake some from 50+mph.

Yeah, but if the light does turn green, you roll right on through! I started FASing like crazy a couple tanks ago and it is REALLY helping. Lightfoot, yes, it cuts off the fuel but the extra drag slows you down alot even in fifth.

I probably would not use FAS if my pack was down at 5 bars or less - or I will probably get into forced regen once I startup/accelerate. Probably would not FAS unless traffic pretty light behind me.

True here too.. but I try to keep off the assist and keep the pack up to 5 bars from the top.. its hard but I am getting better at it.. oh, I put in a Calpod assist defeat (I forget what they called it) to shut off assist, wow, I don't think I could keep 5 bars up without that around here ;)
Gary