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Elk Grove Struggles with Hybrid Buses on Freeways

The Sacramento Bee reports on problems the city of Elk Grove—on the outskirts of Sacramento, California—is having with using its fleet of series hybrid buses for high-speed commuter transport on freeways.

Performance is not ideal, and the air conditioners in the buses are failing in the triple-digit temperatures baking the region this summer. As a result, e-tran, Elk Grove’s new transit agency, will be buying CNG buses for the freeway routes, and using the hybrids within Elk Grove.

“Hybrid may not be the way to go for commuter service,” said e-tran Transit Manager Carlos Tobar, who was hired to run e-tran more than a month after the start of the new service. ”Live and learn.“

So, what’s the problem with the hybrids? They perform best during stop-and-go traffic, Tobar said. The hybrid’s electric energy booster, an ultra capacitor, works in tandem with a 145-kilowatt generator. That booster is recharged every time a driver applies the brakes.

That’s great for intercity transit, but is troublesome on freeways where brakes are less often applied.

“At highway speeds, many of the systems are stressed,” Tobar said.

Elk Grove’s hybrids are remanufactured by Complete Coach Works, using a gasoline series-hybrid powertrain from ISE Corp. The 17-bus e-tran fleet was to be the country’s first 100% hybrid commuter bus fleet.

The ISE powertrain uses a Ford ULEV 6.8-liter V-10 gasoline engine mated to a Siemens ELFA generator and motor system. The dual drive motors each deliver 85 kW (114 hp) of power and maximum torque of 450 Nm (332 lb-ft). Energy is stored either in an ultracapacitor. (Earlier post.)

In the excessive heat this summer, the failure of the air conditioners is a particular problem. The transit agency’s maintenance team has installed new valves and compressors on most of e-tran’s buses and ISE and CCW are tackling reliability issues with the buses—especially the air conditioning.

On days when the temperature exceeds 105, e-tran now provides bottled ice water on each of the commuter routes.

(A hat-tip to Jim Gray!)



What is a matter with these people trying to put hybrid buses on freeway commuter lines? Are they idiots? We have the same idiots here in Washington state as they put hybrids to work in the same situation (sound transit express).

Then, they have to go to an engineering group and pay several hundred thousand dollars for a study which will say "use hybrids for normal stop-and-go bus routes not on commuter routes". When will they start to use their heads?


Then the media ([sarcasm]I love them oh so much [/sarcasm]) will report in big headlines "Hybrid buses don't save fuel; Breaking down on highway!".

There may, at the very end of the article, be a small blurb indicating that hybrids do well when used in the application they are meant for...but otherwise they will be going for the "big" story and all the readers of the newspaper will walk away misinformed (or if they are knowledgeable on the matter: disgusted).

Richard C Burton

gasoline engines-give me a break! My understanding is that in RVs nobody uses gas engines on higher end vehicles due to their proclivity to overheat and wear out quickly- so why would one use them for transit buses?

Charles S

One thought on hybrid design has been more about efficiency for most, if not all stages of driving. It is not necessary that hybrids is supposed to be use ONLY for stop-and-go traffic, but to be more efficient during a stop-and-go traffic.

Just like buying a truck that can haul tons of material, but only used as a commuter car, a bus that was built to meet the most EXTREME situations is wasting energy for normal operations.

Hybrids are not so good when it comes to prolong periods of high outputs. Does that mean hybrids are junk? No, but it also means that current limitations of this hybrid bus makes it a poor candidate for highway+summer driving. Maybe the next gen will do better, who knows.

I agree this is could be sensational reporting, but at the same time, people need to be reminded from time to time that some hybrid designs are more about being efficient, and less about being a full replacement. Every design will have its drawbacks.


Here's a MUCH cheaper solution: Instead of buying a fleet of $200,000 CNG-powered buses, why not mount solar panels on the relatively huge surface area of the hybrid bus's roof? A panel I saw at Epcot in Disney world that was made in 1992 or so was about 1/4 to 1/5 the area of a bus's roof and could provide up to 400 watts of electricity. I am sure a 1600 watt (or more, given today's new thin-film tech and other improvements) would be able to adequately recharge the battery systems to power A/C units- especially on the hot, sunny days when the units were failing.

But then again, what's better than wasting city budget on unnecessary measures?

allen Z

Perhaps a bus would work well on a highway if it was running a route in whicj the exits and entrances are used to access local streets for bus stops. That way, they will travel 1/4 to 1+ miles between stops. That is if there isn't any congestion or accidents.

Sid Hoffman

Joey, 1600w is the equivilent of 2 horsepower. 2hp isn't going to make a bit of difference for a bus trying to do 60mph, which given the weight and aero drag, probably needs well over 100hp, possibly close to 200hp to get up to and hold that speed. I'm sure the 6.8 liter V10 provides a ton of power on it's own, and if even that isn't enough to get the job done, solar panels aren't going to help.


As much as anything else, the transit agency might have been seduced by the notion of being the first to go "100% hybrid." What escapes my comprehension, however, is their failure to anticipate problems on the highway routes. The fact that hybrid technology's strong card is stop-and-go traffic has been well known for years. The fact that a Ford V-10 gasoline engine is insufficient for powering a full size bus at highway speeds with air conditioning running against triple-digit heat should surprise no one. On the face of things, I blame the transit operator and bus purveyor in equal measures for not realizing that these problems might arise.


As much as anything else, the transit agency might have been seduced by the notion of being the first to go "100% hybrid." What escapes my comprehension, however, is their failure to anticipate problems on the highway routes. The fact that hybrid technology's strong card is stop-and-go traffic has been well known for years. The fact that a Ford V-10 gasoline engine is insufficient for powering a full size bus at highway speeds with air conditioning running against triple-digit heat should surprise no one. On the face of things, I blame the transit operator and bus purveyor in equal measures for not realizing that these problems might arise.


That 1600W would be enough to power the A/C for a passenger car.

It wouldn't come close to the a/c demands for a cabin full of people.


For a great example of the city/transportation planners placing the blame on the equipment when it was not used for its intended purpose go to sound transit's website (Washington State puget sound area) and look for their reviews of the Community Transit EXPRESS hybrid buses. They say it failed to meet the fuel economy expectations by a large degree...and they used these buses for EXPRESS routes where you would have 4-5 stops: 1 at a main park & ride transit center, 3-4 at highway stops within 3 miles of the transit center and then the bus would drive 20-30 miles by highway to reach Seattle. The buses for the regular city routes with a stop every 1-2 blocks? Standard Diesel or about backwards.


Series hybrid is awful configuration for commuter bus, not to mention gasoline engine. Parallel hybrid with diesel engine would be comparable with regular bus in fuel consumption on highway and better in city, but even so what is the point to waste hybrid abilities in highway driving?

country mouse

on power for air conditioning, each human being is roughly equivalent to 250 W. of course, that amount of heat into the bus is probably dwarfed by the hundred degree plus temperature on the outside and the energy inefficiency of a bus frame.

As for serial hybrids versus parallel on highways, I have not seen a good analysis of the relative efficiencies of the drive trains. Personally, I find serial hybrids aesthetically pleasing because it opens up interesting options with regards in wheel motors, dynamic Drive control, better antilock, antiskid braking, etc..

In order for a serial hybrids be effective at speed, the average energy output of the generator must exceed the average energy requirements of the rest of the system. Otherwise, you'll never charge the batteries and the system will slow until its energy consumption matches that of the generator output.

tom deplume

I've read that farmers who used R-134a in their tractors A/C also experienced failures in triple digit temps. It is not as good a coolant as R-12 was and is still a low ozone layer threat.


I can't help but wonder about the windows in these buses. How much solar heat do they let in? Hopefully they reflect a large portion of it because 100 plus temps in the Sacto area are not uncommon, IIRC. Is any effort made to insulate the interiors, i.e., is there any insulation in the roof, the sides, etc? This would all seem to help with the amount of a/c needed. Do these a/c systems just run continuously or do they monitor the interior temp and run as needed?

Henry Gibson

The problems with air conditioning have nothing to do with a hybrid bus type. They were just designed and built wrong. R600 (Isobutane) is used in almost every refrigerator built in germany and gives better performance than either R12 or R134a. It is now permitted in all of Canada and Australia for automobiles.

I can't tell from the report, but it seems like the busses were built with only ultra-capacitor energy storage which is absolutely useless for a bus running down the freeway. ISE promotes Ultra capacitors because it looks like there is more power for the dollar, and that works ok if a bus stops every block and restarts. There are full electric busses with no generators operating in California, and some succesfull ones use the ISE other alternative Sodium-Nickel-Chloride.

The Ultra-Capacitors can run a bus for a few hundred feet without engine power, but the battery buses could go for tens of miles.

A lot of money was spent on these busses and the few thousands of dollars extra for a REAL hybrid was not spent in a false economy move. With Zebra Batteries installed to give the same instant power as the Ultra-Capacitors, the bus could be plugged in and run most of the time on electricity at very low cost. The additional expense would pay for itself in a few years at most, and there would even be savings on engine repairs as well. Look for the report on a Bluebird electric school bus that runs somewhere nearby, and the battery city busses in Santa Barbara.

In Europe and Japan all new TOYATA hybrids have a button that allows the full electric running wiithout engine for one mile on the BATTERY. They do not have Ultra-Capacitors because when the car is running down a long freeway slope they want to recover the energy. Ultra-Capacitors can only store a few seconds worth of that energy. ISE has just given hybrid busses a bad reputation and lost the order of a lot of busses by allowing the misuse of a power storage device where a power and energy storage device was needed. It was all for the saving of a few thousand in up front cost that would have been recovered in a few months at the price of gasoline. That is what a hybrid is all about. Search for Maxell's comparison with the ZEBRA on the web or at ISE and see what was said to convince a buyer to save a few buck up front and lose them in the end....

Henry Gibson

I Must correct my previous post.

It was Maxwell that made the capacitors.

By seaching for the buses I found that they do have a limited electric range perhaps 5 to 15 miles.

The gasoline engine seem to have enough generator capacity for the motors.

The spacings are modified but the pairs can be seen

Here are some of the comparisons with Ultracaps.

ZEBRA Battery Pack Thunderpack II
Ultracapacitor Pack

Usable Energy 18kWh 0.3 kWh
Power 32kW Over 150 kW
Energy Density 87 Wh/kg 4 Wh/kg
Power Density 0.16kW/kg 1.5kW/kg
Expected Life 2.5-5 year 10-12 years
System Cost 375 $/kW 100 $/kW
Life Cycle Cost $1125/kW 100$/Kw

System cost $ 667 /kWh $50,000 /kWh
Time at 30 HP 40 minutes 40 seconds
Time at rated power 34 minutes 7.2 seconds

Thunderpack II costs $15,000. It has .3 kwh of energy
storage; equal to 1/60 of the Zebra or equal to 1/4
the capacity of a deepcycle RV battery (12 volts at
100 amp hours or 1.2 kwh). Thundervolt II can produce
32kw for 33 seconds.

The Zebra Battery costs 375*32=$12,000. It can produce
32 kw (42 horse power) for at least 30 minutes.

The new Zebra Battery probably has a useful life of
10-12 years as well even though it is not guaranteed
for that long, so the life cycle cost is probably not
the $1125 $/kw or three times its new system cost.
Unlike lead batteries, the unit can withstand, without
repair, the failure of several cells perhaps as many
as ten percent of them with only a ten percent drop in
voltage and capacity. There is no maintenance cost, and there are no high power semiconductors in the battery to fail.

Stingray transit bus with 12 Zebra batteries can go 130
miles on battery alone.

Refitted school bus can go 50 with 6 Zebra Batteries.

The Elk Grove busses would have to have five or six zebra batteries to run at full power without engine running, but there might be some reason to add more to make it into a plug in hybrid.


Toyota is the leader in hybrid technolgy as well as all things automobile. Why didn't Elk Grove give Toyota the hybrid bus specs and then let Toyota deliver with the guarantees?

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