Hybrids in the carpool lane

I understand that being able to drive in the carpool/HOV lane is a nice perquisite for hybrid drivers. But I’ve heard that hybrids get better mileage in stop-and-go traffic.

Which hybrid burns less fuel? The one in stop-and-go traffic, or the one in the carpool lane? (Not that there’s much difference in flow from what I’ve seen lately. It’s good to be a motorcyclist! :stuck_out_tongue: )

If you think that’s inefficient and silly, here in AZ Alternative Fuel Vehicles are allowed to used the HOV lanes. These are vehicles that can use gasoline, or Compressed Natural Gas. They don’t have to be running on the alternative fuel at the time, just capable of it.

Not making a judgement either way. Just wondering which is more efficient for a hybrid. (CNG cars can use the carpool lanes in CA too. Don’t know about WA. Oh – and you have to have a special sitcker.)

I am curious what the rationale is for this practice, as well as tax breaks and other incentives for hybrid vehicles. Why do we need to incentivize the purchase of vehicles which have a waiting list to buy anyway? How can these perks result in any more hybrids on the road if car companies can’t keep up with demand as it is?

I think the answer is: the slower lane is more energy-efficient.

At constant speed, air resistance is proportional to square of speed. So for a given distance, the energy required to overcome it is proportional to speed. (I.e. if you double the speed, air resistance becomes 4 times as large. But you get to the destination twice as fast, so you “only” use twice as much fuel.)

But in stop-and-go traffic, you need extra energy to start each time. The lower air resistance doesn’t make up for it. But evidently hybrid cars are very efficient at initial acceleration, so the lower air resistance wins out.

You don’t need a hybrid car to see this effect. On my '83 Mercedes 240D, I consistently get 30mpg in “city” (suburban roads, 40~50 mph, usually light traffic), and 25mpg on freeway trips (~65 mph).

Hybrids use the electric motor along with (or instead of, if you accelerate slowly enough and it’s not uphill) the gas engine when they start up. Most hybrids also have regenerative braking, which recharges the battery pack when you brake, so you’re recapturing some of the energy you put into acceleration.

I drive a Ford Escape hybrid, and I can tell you that it gets much better mileage in stop-and-go, low-speed conditions than it does on the highway. The faster you go, the worse the gas mileage. When I drove it cross-country last month, I got an average of 27 mpg; in town, I’m getting close to 30. I’d say those numbers should make cities think twice about rewarding hybrid drivers by letting them drive in the HOV lanes.

I keep hearing “Hybrids are only good for city driving, not so good for highway”.

This has not been my experience, maybe someone here can explain.

Before I bought a Hybrid, I was warned that the MPG that is boasted about by the manufacturers is achieved in ideal test conditions and does not translate to real life. So, I was prepared for my Prius to not actually get the 60MPG City that was promised.

In fact, in the city, I get about 40MPG. A far cry from the promised 60 but my old car got about 13MPG City- so, I am pretty happy with the 40.

On the highway, however, I do get 50MPG just as promised (I’ll generally drive about 70mph).

So, to recap, I get 40MPG City and 50MPG Highway.

What’s up with that?

And not all hybrid/alternate fuel/CNG cars can use the carpool lanes in CA- only certain models.

Screams “kickback” to me, but I’m just like that… :wink:

Perhaps you are accelerating more quickly and more often than the EPA test calls for. Regenerative braking is nowhere near 100% efficient; even on a hybrid, you lose energy every time you slow down and need to accelerate again.

But a ultra-compact diesel car isn’t eligible, even if it gets better gas mileage than a Prius and has less environmental impact during manufacturing and disposal.

I’ve heard that diesels are hard to get in CA. For example you can buy a diesel VW Jetta or Passat (and maybe a New Beetle) in WA, but not in CA.

Well, I guess I won’t get one of those after all. I get better milage than that in my beat-up Passat.

Higher demand (even if it exceeds supply) stimulates production. Maybe they can’t keep up with the demand now, but increased demand will encourage more manufacturing facilities to be brought online and thus bring about more hybrids on the road.

OK, to be fair, California is more concerned about smog than global warming or dependence on foreign oil, so I guess it does make sense. (Diesels aren’t very dirty anymore, but I admit the Prius is probably much cleaner.)

Sorry for the hijack, carry on…

It also depends on the Hybrid system. My Insight was rated at 60 mpg city and 70 on the highway. In reality I averaged 52 to 55 in the city. Lower than expected. On the interstate I managed to average 79 to 85 MPG.
My honda insight hybrid system was designed for long commutes and long drives.
It excels in long drives with little stopping, Toytas system is designed for city driving. Toyotas are a better hybrid for city driving hands down.

Also, how someone drives affects gas milage a great deal. Driving habits are even more apparent in the hybrids than regular vehicles.


It is true, that in certain driving modes, certain Hybrids get better milage drving slower. But that’s not the point- the point is that Hybrids (at elast the 3 that CA allows) get hwaaaaay more milage than their all gas brethen in both modes. Thus, the carpool lane benefit is there to encourage their purchase.

This is also one of the reasons Motorcycles are allowed in the carpool lane, a benefit you enjoy.

Why is that? I’d expect it to be less apparent, for the same reasons they don’t waste much fuel in stop-and-go traffic.

Not true. The hybrid system doesn’t offer any advantage at highway speeds because at constant highway speed, the car is running on its gasoline engine alone. If the Prius gets better highway mileage than other comparable cars, it’s only because of its aerodynamic shape.

My wag is that drivng carefully (in regards to MPG), allows the batteries to last longer before needing the gas engine to kick back in, and when the gas engine is running by driving carefully you can recharge the batteries quicker and switch back to all electric mode sooner.

I Think you are oversimplifying things a bit too much here. I believe at highway speeds, as long as you are not using the a/c, perhaps the heater as well, that the car can still cycle between battery and combined drive.

But even if the gas engine is running, it can run at it’s more efficinet setting and let the electric drive system make of the difference when more power is needed and shunt power into the batteries when demand for power is less then the most efficient, In other words the gas engine can always run at it’s most efficent rpm’s and throtle position as long as enough power is being produced to meet the average demand on the car - the electric system will make up for the peaks and valleys of demand.

But all cars do that, on the highway. If you know what speed you’re optimizing for when you build the car, then you can just put in the right set of gears, and when the engine is running at its optimum RPMs, in that gear, it’ll be going at highway speeds. It’s only for city driving, which isn’t so consistent, that you can do better than the handful of fixed gearings.

I agree that hybridity (hybridness? hybridosity?) offers no advantage in constant-speed highway driving. There are reasons other than aerodynamics, though, that the Prius gets good highway mileage - for example, low rolling resistance and a drive train that allows the engine to run at the most efficient speed regardless of the speed of the car.