2006 Lexus RX400h: Engine braking optional

I agree with the blog... to a point. I think a lot of people brake unnecessarily, and I would *love* to slalom around cars on the interstate, but due to the inconsistencies of drivers and their propensity to freak out and do something erratic instead of holding their course makes this a pretty dangerous venture.
 
On a semi-related note, I think that the gradient brake lights that some auto mfgs are starting consider might help this.

Whoever drives manual will understand this post. Those who don't will be perplexed. I don't think anyone driving an automatic gives any thought to the process. They just steer.

I imagine the theory is that the first guy to encounter congestion taps his brakes to slow from 70mph to 67. The guy behind him doesn't know what the first guy is doing so he slows to 65mph. The next guy slows to 63mph and so on until somewhere in the back of the pack everyone is at a dead stop. Of course, this assumes that all drivers are inattentive/stupid. But then again, this is L.A. we're talking about...

Great post. I think excessive brake use has always been an unfortunate side-effect of automatic transmissions, and leads to unnecessary braking from most other drivers within view. Manual drivers exploit this characteristic, and in the process keep traffic flowing freely, use less gas, and extend brake lining life.
 
I'm a little surprised that the RX400h doesn't do this on its own, like some hybrids. My wife's VUE Green Line regenerates power upon coast, leading to engine braking much like a manual or an auto with a very tight torque converter. Must be a characteristic of the CVT, as our GL has a traditional 4-speed slushbox.

"I imagine the theory is that the first guy to encounter congestion taps his brakes to slow from 70mph to 67. The guy behind him doesn't know what the first guy is doing so he slows to 65mph. "
 
wrong explanation.
during driving: 2 car distance spacing.
stopped: 3 foot spacing.
 
When a traffic comes to a stop/restart, the following distance has to rebuild.
You can't immediately go as fast as the car in front of you, you wait for the following distance to rebuild, hence the wave-like gesture of the sea of cars.
Identical to the contractile motion of a catepillar's body.
 
So what caused the very first cars (catepillar's head) to slow down so much in the first place?
highway exits (0-40 mph, 0 mph if the red stop light backed up onto the highway),
highway transition ramps (40-60 mph), taking you onto another highway,
lane merges,
construction somewhere in the city,
distracted drivers,
slow drivers,
near accidents,
foreign objects on road,
accidents,
events/accidents near the highway that cause people to look,
and whatever else.
 
Today's congestion comes from the #cars:#roads ratio increasing by 10x from years past. We simply have not built more roads at the same rate more cars are built; only at 1/10th the rate.

"Would it not improve everyone's fuel economy?"
 
what kind of physics class did you take?.....
constant loss of power to overcome engine friction in no way helps fuel economy.
 
Manual transmissions conserve more energy than autos when the car is driven forward, but lose more energy than autos when getting dragged down by engine braking.
 
With an auto, you learn to take your foot off the accelerator earlier than on a manual. Your driving habit is incorrect for autos.

This helps explain why journalists, aka manual enthusiasts, can't get the sky high mpg readers can get.
 
In an automatic: no pedals = car continues moving forward, at 99 mpg.
In a manual: no pedals = car slows down considerably, 99 mpg.
 
You need to add a "no pedals" stage to your driving, to average in more 99 mpgs to raise your mileage.
If you have an instantaneous mileage readout screen, such as on the RX400h, you can see this.

Most cars will shut off fuel delivery while engine braking in gear, down to a certain RPM. So yes, engine braking is more efficient.
 
Instantaneous MPG indicator is nothing more than a manometer that is calibrated to show approximate MPG based on engine vacuum. There is no magic fuel calorimeter that calculates the actual mileage.
 
Also, you are forgetting that with manual you can control the process. You can either use engine braking to slow down (and save fuel) or select neutral position and coast.
 
My understanding of the problem described by the original blog post is that automatic drivers will typically engage their brake lights at the slightest perceived need to slow down. In many cases the driver does not intend to actually slow down at all, just moving their foot on top of the brake pedal in anticipation. Or they slow down very slightly, by only a small increment. The driver following at a safe distance may not have any way of knowing that the first person does not intend to slow down much. The second driver also engages his brakes, slowing down much more than is necessary in this situation. The third driver behind the second one slows down even more, and so on, until you have a traffic jam (or an accident).
 
 If the first driver were driving a manual car, instead of putting his foot on top of the brake pedal and engaging the brakes, he would slightly slacken the pressure on the gas pedal. The car would respond immediately and directly because that's how manual transmissions work. The following driver would not see the brake lights go on and would not put on his brakes. They both would continue driving at constant speed. The net result of this would be smooth flow of traffic vs. a potential traffic jam.
 
I see this problem happening all the time. As a matter of fact, I consciously try to smooth out the flow of traffic by keeping a safe following distance and minimizing the use of my brakes.

I thought I was the only one who cared about engine braking. I'm currently on vacation, driving a rental Impala with an automatic, and the lack of engine braking annoys me to no end. The Impala could be a great car for all I know, but I can't get past the fact that it will happily continue driving at 35 mph even when my foot is off the gas.

vvk--Excellent points.
 
After reading Josh's post, I knew he was right, but wanted to test it out anyway. Last night while driving in traffic in our long-term G35 with the 6-speed manual I decided to take note of how often I braked in comparison to the cars in front of me (that were clearly automatics). I didn't change the way I normally drive. Sure enough, I braked significantly less than the cars in front of me and really only when they came to a complete stop. I also followed at a car-length distance versus the three-bumper-length distance of the auto-equipped cars. Of course, I have no way knowing whether the cars behind me were forced to brake as well, but like vvk I also find myself trying to "break" jams by keeping my distance and not breaking. I consider it a public service.

As a confessed engine-braking fiend, I feel Josh's pain. And yes, the continuous cycle of slowing down and speeding up of traffic degrades fuel economy. Autoboxes have the additional penalty of having to churn through the torque converter (prior to lockup) each and every time.
 
By the way-- did anyone catch the movie reference in his blog entry?

By the way, June is Lane Discipline Month (as decreed by the NMA). Tell your friends and neighbors!

http://www.amasci.com/amateur/traffic/traffic1.html has some good related reading.

vvk: Some of the newer on-board mpg calculators are pretty accurate, as many are not just simple manometers. The ECU can calculate how much fuel is being squirted into the engine by assembling data from a number of sensors.
 
As we all know, the ECU knows engine rpm, how long each injector is open, fuel pressure, and a host of other parameters. So even though there isn't an actual flow meter involved, its knows to a much higher degree of accuracy than any manometer. Displaying this in the cabin is all a matter of talking to the ECU.
 
Carburetors could never do this, because they just suck. (fuel, that is)
 
 A recent fuel economy test using our long-term Tahoe produced repeated on-board MPG radings that were spot-on with our hand calculations every time.

no manumatic / tiptronic in such an expensive car ?!

The answer to that question is a question: A Lexus hybrid owner wants to manually shift gears? No' bloody likely.

tirthankar, the RX400h has a CVT. A few manufacturers give their CVTs a "manumatic" mode with simulated fixed ratio selection, but I have yet to see a performance gain from this. As another poster mentioned, it's really just a "feel good" feature, unlike geared manumatics that have actual functional advantages.
  
Engine braking is very efficient, for the reasons that wk mentioned. My instant mpg reading goes way up when I use engine braking on deceleration versus using the brakes to decelerate at a similar rate.
  
I am also in the camp that uses brake lights as sparingly as possible on the freeway. I'm glad I'm not the only one that understands that if more people did this, it would actually reduce highway congestion! A University of Michigan study concluded that if 20% of the cars on a single lane road following a "slow car" were using Distronic ACC (does not activate brake lights when slowing down), the stand-still congestion this situation otherwise created was eliminated. The reason is that ACC reacts quickly and accurately to changes in speed, versus the human problem of reacting too slowly and/or excessively - creating the traffic accordion. So, ACC essentially reduces this "dumbass" effect.
 
Don't even get me started on lane discipline... I am tortured up here in NorCal. At least in SoCal many people are too terrified to hog the left lane. =P

bimmerjay, it's that the drivers are terrified of leaving the left lane here in SoCal-- they pile into the left lane like you wouldn't believe. Like they're giving out free botox on the median. It's absolutely infuriating.
 
I'm convinced that we don't need more freeways or travel lanes or carpool lanes to improve traffic flow. Lane discipline would go a long, long way towards resolving the situation.
 
Once the US has reached the lane discipline adherence of, say, Germany, then sure--go ahead and build more freeways.
 
Unfortunately, actual driver training is a foreign concept in the US. Lane discipline will happen here when frost forms on Satan's El Camino.

I thought Satan's ride was a red Ranchero with twice pipes.

lol jkavanagh - I was driving around in Europe only a few weeks ago, and I continually annoyed my passengers with my astonishment at the lane discipline! On a 3-lane motorway with me in the center lane, cars approaching to pass that were in the center or RIGHT lane would always move all the way to the left lane to pass me, then move back over immediately. Sometimes a car would get out of the left lane so quickly that it would almost cut me off. Unless it was congested and unavoidable, cars never passed on the right and nobody dared to sit in the left lane.
  
I would strongly support much more rigorous driver training the United States - and raise the minimum driving age... lousy teenage punks! Get rid of the sense of entitlement Americans have about driving cars and restore a respect for the rules of the road.
  
Rant complete.

I also try to "prevent" traffic jams by coasting when I see brake lights in front of me. If you're not following too closely, you have some room to play with and you can allow the guy in front to resume his speed without causing the guy behind to hit his brakes as well. There's one advantage of an SUV, I can see what's happening several cars ahead, so I know if I really need to brake hard, or if the idiot in front of me is just over-reacting.