What would the $5.2 billion transportation tax increase cost you?

[kphoger]

Perhaps I am not flooring the gas often enough or long enough, but I have never been able to see the effect of a difference in driving style in tank averages.  I generally find that fuel economy is influenced by (in rough descending order, the actual sequence varying slightly from model to model) city versus highway driving mix; relative wind speed and heading on mostly-highway trips; frequency of cold starts; ambient temperatures; tire inflation pressures; and A/C use.

The hierarchy of difference-makers for me would go like this:  City versus highway driving (most of my daily commute is highway driving, so I don't see the effects of this as much as someone else might); Cold temperatures; Wind direction especially if using the car-top cargo box; RPM during acceleration; Cruising speed especially if using the car-top cargo box; Tire inflation.

I first noticed the correlation between accel rate and fuel economy with our previous vehicle, a 2004 Grand Caravan, which did not have an MPG calculator.  Reducing the RPM during acceleration by 5000 RPM made more of a difference than reducing top speed by 5 mph.  This is part of why cold temperatures sink my fuel economy, as my car insists on shifting at higher RPMs when the engine is cold.  Now that I have an MPG calculator, I see the difference very starkly shortly after filling up (or at least I used to back when I kept my display set to show that).

Back when I used to drive an Isuzu turbo-diesel cab-over box truck for a living, I could count on exactly 300 miles to a tank no matter what.  It didn't care how heavy the load was, it didn't care what my top speed was, it didn't care how I accelerated, it didn't care which way the wind was blowing.  300 miles.  The engines in large, boxy vehicles are already built to overcome weight and wind drag, so adding weight and wind doesn't affect them very much.  This is why putting a huge Sears X-Cargo box (and not the newer aerodynamic ones) on top of our SUV only drops the mileage from highway average to city average, whereas people who put those things on small sedans report seeing more marked drops in fuel economy.

However, I still fail to see how hard braking expends more fuel.  If I take my foot off the gas pedal as soon as the next light down the road turns red, what difference does it make how long I coast before stepping on the brake?  In fact, if I expect the light might turn green before I get there, I might even save gas if I don't brake gradually, because then I wouldn't have as far to go to get back up to speed.

The efficiency gains from coasting and braking vary from model to model because they depend on how deceleration fuel cutoff is programmed, how the transmission behaves when the throttle is closed/the accelerator pedal position sensor tells the PCM driver power request is nil, etc.  As an example, some economy car automatic transmissions (Saturn SL2, Honda Fit, etc.) stay in lockup in the lower gears, so DFCO is usable without stalling the engine and compression braking is readily available, while the Toyota corporate approach to transmission design is to provide one-way gearing in the lower gears for D (not L3, L2, etc.), so that when you take your foot off the pedal, the engine goes straight to an idle and there is no compression braking.  (Compression braking for hill descents etc. is still available, but the transmission actually has to be put in a L range.)

As a very broad generalization, foot off gas = throttle closed = minimum amount of air getting into the engine = less fuel to make a stoichiometric mixture = less fuel consumed.  But, as is the case with acceleration, the effect is subtle enough that it doesn't really show up in tank averages.

Maybe I'm misunderstanding your reply, but you seem to be disregarding what I highlighted above.  My foot is off the gas pedal for the duration in both scenarios.  In one I brake gradually, and in the other I brake suddenly.  How is there a difference?  If there is none, then people need to stop touting gradual braking as improving fuel economy.

[J N Winkler]

The hierarchy of difference-makers for me would go like this:  City versus highway driving (most of my daily commute is highway driving, so I don't see the effects of this as much as someone else might); Cold temperatures; Wind direction especially if using the car-top cargo box; RPM during acceleration; Cruising speed especially if using the car-top cargo box; Tire inflation.

Based on what you have said elsewhere in this forum, I'm guessing you have a one-way commute of about 12 miles (subdivision catercorner from where Southeast High School used to be to somewhere near 61st North and Hydraulic), and are therefore cold-starting the engine 25 times per tankful of commute mileage.  Your current vehicle is probably quite good at warming up quickly, but even so I'd estimate the repeated cold starts are giving you a 2-5 MPG penalty (slightly steeper in winter) compared to 300 highway miles with just one cold start.

I first noticed the correlation between accel rate and fuel economy with our previous vehicle, a 2004 Grand Caravan, which did not have an MPG calculator.  Reducing the RPM during acceleration by 5000 RPM made more of a difference than reducing top speed by 5 mph.  This is part of why cold temperatures sink my fuel economy, as my car insists on shifting at higher RPMs when the engine is cold.  Now that I have an MPG calculator, I see the difference very starkly shortly after filling up (or at least I used to back when I kept my display set to show that).

I think that Caravan had other problems as well.  Didn't you mention having to do a shadetree replacement of the catalytic converter?  I strongly suspect you had a bad thermostat or a failed coolant temperature sensor--quite probably both given the American manufacturers' history of using resin-tipped coolant temperature sensors.  Failure of either part biases the engine to run rich (in the case of the sensor, this is because software workarounds for bad input have to bias richward since running lean kills the engine a lot faster than running rich), and that in turn kills the catalytic converter over time.

I don't think you should have been seeing a cold shifting regime after more than two miles of highway driving, even in bitter cold.  This would also point to sensor failure even though the transmission has its own separate fluid temperature sensor.

My Saturn has a cold shifting regime with noticeable displacement of shift points in cold and outright prohibition of certain gears below 10° F, and it is usually out of this regime within a mile of road load.  I don't idle it to warm it up either.  However, this is with thermostat, coolant temperature sensor, and transmission fluid temperature sensor all replaced in 2014.  (Setpoints went up slightly with the new thermostat, and the old coolant temperature sensor was definitely bad since the resin tip had cracked.)

Maybe I'm misunderstanding your reply, but you seem to be disregarding what I highlighted above.  My foot is off the gas pedal for the duration in both scenarios.  In one I brake gradually, and in the other I brake suddenly.  How is there a difference?  If there is none, then people need to stop touting gradual braking as improving fuel economy.

I was speaking in very general terms.  In the specific case you describe (foot off the gas and thus throttle closed a fixed distance away from the next signal), I think the savings associated with gradual braking versus extended coasting followed by relatively firm braking are slight, dependent on control programming, and likely to go in either direction.  However, I do not think it is wrong to tout gentle braking as a fuel-saving technique.  The reality is that it goes hand in hand with extended coasting because it is refraining from bombing along to the next red light/other obligatory stop with throttle part open that makes gentle braking possible in the first place.  In fact I'd say both sides of your scenario amount to gentle braking, one being just a little more firm than the other.

Another consideration is that, in a given gear, the more slowly you are moving and the further away from the red signal you are, the more flexibility you have in timing your arrival so that you can go through on a fresh green without having to stop and wait, or slow down further (maybe even forcing an unwanted downshift) and hang behind to give other vehicles waiting at the light time to go through, get up to speed, and develop an adequate headway for you.  For lights I know well, I often have a point I aim to be moving past at a given speed when I see that they are red--a point that moves further back the more traffic is queued at the light--and I try to arrange things so that I can coast down to the desired speed at that point without having to use the brakes.

[kphoger]

Based on what you have said elsewhere in this forum, I'm guessing you have a one-way commute of about 12 miles (subdivision catercorner from where Southeast High School used to be to somewhere near 61st North and Hydraulic), and are therefore cold-starting the engine 25 times per tankful of commute mileage.  Your current vehicle is probably quite good at warming up quickly, but even so I'd estimate the repeated cold starts are giving you a 2-5 MPG penalty (slightly steeper in winter) compared to 300 highway miles with just one cold start.

Approximately right, yes.  I never let the engine idle for more than just a minute before driving away, as this can lead to an improper fuel mixture for the catalytic converter and is little useful in these days of fuel injection (exception being when I'm running the defrosters on thick ice and snow).  And yes, it is quick to warm up; last winter didn't get bitterly cold enough for me to straight-up compare it to our old one, but it seems to do better than the GC.

I think that Caravan had other problems as well.  Didn't you mention having to do a shadetree replacement of the catalytic converter?  I strongly suspect you had a bad thermostat or a failed coolant temperature sensor--quite probably both given the American manufacturers' history of using resin-tipped coolant temperature sensors.  Failure of either part biases the engine to run rich (in the case of the sensor, this is because software workarounds for bad input have to bias richward since running lean kills the engine a lot faster than running rich), and that in turn kills the catalytic converter over time.

I don't think you should have been seeing a cold shifting regime after more than two miles of highway driving, even in bitter cold.  This would also point to sensor failure even though the transmission has its own separate fluid temperature sensor.

Yes, the catalytic converter was replaced in 2010, if memory serves.  It was installed backwards, leading to the downstream oxygen sensor being completely shorn off due to contact with the vehicle body.  We drove it that way for six years and approximately 100,000 miles.  The cooling system appeared to be in good working order, or at least it seemed to function appropriately when the radiator developed a leak a couple of years ago.  And I should have been more specific to your last point:  shift points normalized after about five miles of driving in the bitter cold, more like the two miles you expected in more normal cold weather.  But I've noticed delayed shifting in cold weather no matter what vehicle I was driving, and I still think it's part of the reason fuel economy suffers in the cold weather.

[Sykotyk]

I've noticed that the extra gallon in the tank or more will vary by automaker.  Fords usually would let you go much further down into that last gallon before the gauge would go to E or the range meter would display empty.  The estimate on a tank really varies depending the automaker as well. Both Ford and GM vehicles seem to base the estimate off the last fuel run whereas Chrysler cars seem to change during the tank you're on wildly depending on how you drive. 

I have a Hyundai Sonata Eco. Based on the size of the tank and MPG, the tank should get about 700mi on highway travel. However, based on regular driving, 600mi is about the absolute max. But, when you fill the tank, the computer resets the 'miles until empty' guage to usually around 550-560 miles.

However, once you get to 50 mue, when the dash light comes on, it starts dropping much much slower. That final '50' miles turns into about 100 miles. I drove the car roughly 15 miles on 8 mue. Not exactly optimal since you don't want to run out with newer fuel injection engines, but we were out in nowhere. The thing is, when we gassed up, we were still over a gallon shy of filling the full tank. Almost 2 gallons.

So, we know that the 'low gas' light is nowhere close to honest. But, it is nice going about 500 miles-plus on one tank. My old car had a bad gas gauge and you couldn't trust it anywhere after 200mi. Which meant fueling frequently just to be safe. I kept track of mileages per gallon, and it averaged about 18-25mpg. Which on a 16g tank made a huge difference to how many miles you could go on a tank without risking running out.

[Sykotyk]

I was speaking in very general terms.  In the specific case you describe (foot off the gas and thus throttle closed a fixed distance away from the next signal), I think the savings associated with gradual braking versus extended coasting followed by relatively firm braking are slight, dependent on control programming, and likely to go in either direction.  However, I do not think it is wrong to tout gentle braking as a fuel-saving technique.  The reality is that it goes hand in hand with extended coasting because it is refraining from bombing along to the next red light/other obligatory stop with throttle part open that makes gentle braking possible in the first place.  In fact I'd say both sides of your scenario amount to gentle braking, one being just a little more firm than the other.

Another consideration is that, in a given gear, the more slowly you are moving and the further away from the red signal you are, the more flexibility you have in timing your arrival so that you can go through on a fresh green without having to stop and wait, or slow down further (maybe even forcing an unwanted downshift) and hang behind to give other vehicles waiting at the light time to go through, get up to speed, and develop an adequate headway for you.  For lights I know well, I often have a point I aim to be moving past at a given speed when I see that they are red--a point that moves further back the more traffic is queued at the light--and I try to arrange things so that I can coast down to the desired speed at that point without having to use the brakes.

My point about gentle deceleration was the simple idea that some people will see a red light, but instead of immediately letting off the throttle, will continue at speed until they have to brake. Even with traffic in front of them preventing them from zooming through the light if it changes green before slowing.

Once a light changes, you should begin to coast from any distance to the light. Unless far enough where one full cycle of the light might happen (then you'd hit the second red, but you'd have to know that in advance and be generally aware how long the light lasts). But, the odds of 'keeping speed' and making it through the resulting green is less likely than coasting at the first sign of the yellow (even far back), so that when it does turn green barely any further shot at deceleration is needed in comparison. Especially with traffic ahead of you (stopped or otherwise).

It's the length of coasting that matters, not that you are coasting/stopping/slowing. If you coast for 400 feet compared to 200 feet, you've just drive with fuel pumping for 200 feet that became completely pointless. That's wasted energy. And it adds up during a city commute where your top speed never reaches top gear for quite long periods, before the next light.

[kphoger]

I was speaking in very general terms.  In the specific case you describe (foot off the gas and thus throttle closed a fixed distance away from the next signal), I think the savings associated with gradual braking versus extended coasting followed by relatively firm braking are slight, dependent on control programming, and likely to go in either direction.  However, I do not think it is wrong to tout gentle braking as a fuel-saving technique.  The reality is that it goes hand in hand with extended coasting because it is refraining from bombing along to the next red light/other obligatory stop with throttle part open that makes gentle braking possible in the first place.  In fact I'd say both sides of your scenario amount to gentle braking, one being just a little more firm than the other.

Another consideration is that, in a given gear, the more slowly you are moving and the further away from the red signal you are, the more flexibility you have in timing your arrival so that you can go through on a fresh green without having to stop and wait, or slow down further (maybe even forcing an unwanted downshift) and hang behind to give other vehicles waiting at the light time to go through, get up to speed, and develop an adequate headway for you.  For lights I know well, I often have a point I aim to be moving past at a given speed when I see that they are red--a point that moves further back the more traffic is queued at the light--and I try to arrange things so that I can coast down to the desired speed at that point without having to use the brakes.

My point about gentle deceleration was the simple idea that some people will see a red light, but instead of immediately letting off the throttle, will continue at speed until they have to brake. Even with traffic in front of them preventing them from zooming through the light if it changes green before slowing.

Once a light changes, you should begin to coast from any distance to the light. Unless far enough where one full cycle of the light might happen (then you'd hit the second red, but you'd have to know that in advance and be generally aware how long the light lasts). But, the odds of 'keeping speed' and making it through the resulting green is less likely than coasting at the first sign of the yellow (even far back), so that when it does turn green barely any further shot at deceleration is needed in comparison. Especially with traffic ahead of you (stopped or otherwise).

It's the length of coasting that matters, not that you are coasting/stopping/slowing. If you coast for 400 feet compared to 200 feet, you've just drive with fuel pumping for 200 feet that became completely pointless. That's wasted energy. And it adds up during a city commute where your top speed never reaches top gear for quite long periods, before the next light.

Yes, I follow.  But then fuel economy is not a matter of braking, but rather one of coasting.

[bing101]

http://www.ttnews.com/articles/californias-new-gas-tax-approved-caltrans-hiring-spree-construction-work-ramps


Update The gas tax includes more hires at Caltrans.

[Quillz]

Death, potholes, and taxes...

Hey, if we get better roads out of this, whatever. I've gotta pay for gas anyway.

[DJStephens]

What is the current status of Brown's "fantasy" train?  Have heard cost estimates for that - as approaching $68 Billion.