Is it worth stopping to get to S4?

Probably not, unless you have a stretch below 30 mph. S4 advantage over S3 is the ability to properly glide without needing to go over 35 mph. (I'm assuming you have a Gen II Prius, it's not in your profile). On a 55 mph road the question of gliding is moot anyway.

I have a similar dilemma, but the speed limit on my road is 25, people go 30, but there's cops occasionally and they'll gladly pull you over. So do I risk going up to 35 and then glide down the big hill I have (relatively speaking, it is Chicagoland after all), or do I stop someplace before that, lose my momentum, but I can glide without accelerating above 35, or do I just coast down with the engine still on and go into S4 at the next stop sign. It kind of depends on traffic and mood for me.

 

Very close call, but IMO you're probably better off going with S3a if a large majority of the time after the light is spent at speeds above 41mph since your ice wouldn't be shutting down anyway. I'm not sure if you'd be able to recover from the hit you'll take getting to S4 quickly before you arrive at your destination.

But it seems like it would be such a close call that your best bet is to try both and see which one works better.

 

I frequently pull off to a side street to get into stage 4 if I'm getting to a certain part of the trip with lots of stoplights or if I know I'll be going under 35 mph. In my case it's well worth it to avoid having the engine run for several miles when not needed.

 

I use my MCU controlled ECT Spoofer to go from S1a to S3 stage then I slowly glide idling to the next RED light where the car will drop into S4 within another 5 seconds and shut the ICE off.

So the steps are for starting below 80F in the mornings around here (Atlanta) is:

S0----->S1a-----@112deg F----->S3----idling check ceremony---->S4

Lately I have been seeing MPG readings on the ScanGauge for my 23 mi morning commute ranging from 63mpg to 74mpg.
Returning from the Farmers Mkt food shopping on a 80 deg day and 30 min shopping stop the car returned 76mpg. The Spoofer tipped it into S4 at the Traffic Lights at the Exit from the Mkt.

 

How long after you get to S4 will you be gliding for? Is your terrain flat?

In general my guess is that it is worth it. With a cold ICE the amount of gas needed to reach the pre-light 35 mph or 20 mph will not be very different. Assuming that you are braking slowly you are only losing SOME of the momentum, however a lot of it is regenerated and stored as increased SOC. That SOC will be really useful in S4.

Like Mike I often stop to get into S4 if the traffic lights don't cooperate.

 

I can only imagine SUV drivers' reactions to all the stationary Prii found on the side of the road:

"Oh, honey, look, there's another one of those hybrids broken down, that's the fifth one today! Probably the $10,000 battery going kaput after a year or two, like on all those things."

 

Terrain is gently rolling, I guess I should have said crawling if traffic allows. The ECU needs around 12 secs to re-cal the Idle. I sometimes have a few seconds idle at the next light but I think it is going thru the evap canister purge cycle.

I tell the guys at work that I save 2 teaspoons of gas every warm-up cycle with this device.

If the light or traffic do not co-operate I just keep on moving as I will get caught by a light sometime as I have to go thru 23 of them in to work.

 

Uphill or downhill? For me, when it's uphill, of course don't stop, since no gliding is possible. If downhill, and there is a place to stop, then I do. Some of the hills around here are steep enough that taking my foot off the brake is all I need to get going up to speed again.

There's not much flat terrain here. If it does happen to be flat, then it would depend on how long I have until a possible natural stop (such as a red light). I consider gliding at 35+ to be a last resort.

 

You can try a hedge: sit in park for 15 - 30 seconds with the ICE running before you drive off.

 

What is S4, S3 ? I have a gen.3

 

^^ engine warm up phases. Few people want to know.