ISE Receives Order for 25 Gasoline Hybrid-Electric Drive Systems for Long Beach Buses
GM Introduces Higher Fuel Economy Version of the Cobalt

San Diego Launches CNG Hybrid-Electric Bus

The CNG hybrid bus.

The San Diego Metropolitan Transit System (MTS) has launched its first commercial bus with a Compressed Natural Gas (CNG) hybrid-electric drive system (CNG Hybrid Drive System). ISE Corporation (ISE) developed and supplied the system, a variant of its ThunderVolt gasoline hybrid drive, and integrated it into a standard 40-foot transit bus supplied by MTS.

The $1-million CNG hybrid prototype bus will further cut emissions and fuel consumption of the CNG buses in the MTS fleet, providing more power and a quieter ride. Funding for the program was provided by grants from the South Coast Air Quality Management District (SCAQMD), San Diego Air Pollution Control District (APCD), and the California Air Resources Board (CARB).

This new technology is important to California transit agencies that have invested heavily in CNG infrastructure and are seeking even more efficient power drives. The CNG-electric hybrid technology represents the next step forward in our commitment to a healthier environment.

—San Diego County Supervisor Ron Roberts, who also represents San Diego on the boards of directors of MTS, APCD and CARB

The CNG Hybrid Drive System features a Cummins ISB Gas Plus engine, a Siemens 165 kW electrical generator, two Siemens duo inverters, two Siemens 85 kW drive motors and Cobasys-developed NiMH batteries. MTS provided a New Flyer bus for the program and New Flyer assisted ISE in the modification of the bus chassis.

The addition of the new CNG hybrid bus to the MTS fleet comes in conjunction with the recently authorized MTS purchase of up to twenty 35-foot gasoline hybrid buses for delivery this fall, and up to 250 40-foot conventional CNG powered buses or gasoline hybrid powered buses over the next five years. The new order of buses will be the biggest procurement order in the history of MTS.

Currently MTS maintains and operates 476 buses of which 75% are CNG. The new CNG hybrid bus and the new bus procurement will align MTS with its stated goal of converting its entire fleet to CNG or hybrid technology within the next 6 years.

The CNG hybrid bus will travel all over the MTS network, providing commuters the opportunity to experience the new technology.



I am not sure about the hippy dippy Greatful Dead Woodstock paint job, but they are on the right track. Do some turbo compounding with heat recovery and they might really have some efficiency.

Gerald Shields

Uh SJC, The Greatful Dead lived in California. :(

Harvey D


It is great to see the California is leading the nation once again.

What could be the total GHG and liquid fuel reduction potential per bus (or per mile) with a fully optimized CNG Hybrid Bus with waste heat recovery etc over a standard diesel bus of similar capacity?


I do not know. We read about 3 mpg begin par and maybe 4 mpg with hybrid. Compounding and vapor turbine maybe 5 mpg? That is WAG (Wild A** Guess) but you start to get nearer to fuel cell territory.

CNG has 100k BTU per therm (100 standard cubic feet of volume at 1 atmosphere) gasoline 120k and diesel 140K per gallon? It might be good to rate it as miles per BTU but I have seen gasoline gallon equivalent expressed.

The Clean Energy guys claim 40% mileage gain with just the vapor heat recovery, but I will believe that when I see it. The compounding guys have claimed 10% better mileage for large trucks. So both combined might be 25%, being conservative.

SAE, Cummins (link attached), Deere and others have been working all this out for years and there are slides and papers on the web about it. But 100,000 miles per year at 4 miles per gallon is 25,000 gallons at $4 .50 per gallon is $100,000 per year fuel costs. If you can save even $10,000 per year in fuel, that might pay for some hardware.


Look closely, it's not a Greatful Dead motif. It's more of a Thomas Hart Benton mural.

Harvey D

Thank you SJC for the info.

Improved CNG buses,
even at 5 MPG equivalent, would be a lot less efficient than electric city buses with automated quick charge at every (major or every 10th corner stop or so) to avoid overhead wires. Automated recharge bus stops could be designed in such a way as normal trafic is not hindered.

Depending on the energy capacity of the battery packs used, the number of quick recharge stops could be reduced or increased.

With enough recharge stops, they could become fully transparent to the users. The time normally required to offload and/or load 10 to 20 people should be enough to get a quick recharge.

An emergency on-board mini genset would supply enough power to crawl to the next charge stop, when needed.


I like that. I figured with CNG being 30% less GHG and using less they might cut the GHG output in 1/2 compared to diesel non-hybrid, which is not bad. Just getting rid of the particulates is a plus. The electric bus idea is kind of like the partial electric rail idea, you run and charge when you can off the grid.

We had overhead wires in the new light rail and I was not impressed. The only thing I wanted them to do was put solar panels on all the bus stop roofs. They had a lot of square footage to keep rain and sun off the passengers waiting.

I suppose they could put inductive strips in the roadway and you might be able to charge off that, but not a lot. I think the Capstone turbines with a combined cycle vapor turbine will take over until they can get fuel cells. You can run those off of CNG as well. CNG is half the price per BTU as diesel, you do not use oil, you do not have to refine it nor transport and store it.

Harvey D


If an all electric truck can go 100 miles between charges, can we presume that an all electric bus, with improved batteries, could go at least 50 miles?

If so, battery operated city buses would quick recharge at the end of their normal run only (where they normally stop for about 10 minutes anyway).

The infrastructures required would be reduced. You cannot get a cleaner more efficient bus than an All Electric One. Zero emissions, much lower noise pollution, less brake wear and noise, much less maintenance, higher availability, no reduction (but increase) in comfort etc. One could have traction on all wheels for slippery winter days, where needed.

I strongly believe that we will have all electric battery operated city buses soon after battery price drop to $200 KWh. SuperCaps-Battery combo would be ideal to recuperate more breaking energy, give more initial torque to get moving and to extend battery's life.

Wouldn't be surprised to see a few of them in operation in China's major cities much sooner than we think. A few (smaller) experimental units will be ready for the 2008 summer Olympics. Larger units will be common place a few years latter.


One of the posters said that city buses put on 30,000 miles per year, 300 days time 100 miles per day sounds about right.
That would be a lot of batteries if the bus can go 1 mile per kWh, but not out of the realm of possibility. Charging 50 kWh in 10 minutes might be a bit of a challenge however. You would have to have 300 kw of power or more than 300 volts AC three phase at 1000 amps. That would be a mighty big plug. More like 440 VAC three phase, depending on pack voltage with 800 amps service. I suppose this is not unheard of. That might be enough to power 50 homes or one major office building, but doable.

Harvey D


The average city bus run (one way) is between 12 and 24 miles depending on the size of the city and run characteristics.

At one mile/KWh, we are talking about 12 KWH to 24 KWh recharges (in 10 minutes each) 6 to 10 times a day.

Note: That could be reduced with the use of complementary supercaps.

Electrically speaking, that is very doable. No new technology is required.
A standard 660 VAC, 3-phase charger could (easily) be built to handle that much power. To make things even easier, the battery pack voltage could be equivalent, reducing the need for voltage step up or step down.

Much bigger problems have been solved.


I do not think it is a problem, just sizing up the situation. Stopping for 5 minutes are the end of a 1 hour run does not seem like a big thing. Inductive pads could be used so the driver just parks and pushes a button. Much safer in the rain also. I like the idea and I think it could work.

Harvey D


Yes, a 100 KWh to 200 KWh induction pad could be used. The secondary bus mounted part would be a bit heavy. Proper alignment should not be a major problem with bus wheel tracks and coil pad lift mechanism.

The induction loss could low. Would this type of induction coupled charger be as efficient as a direct connection charger? It would definately be safer to use.


The paddle system on the EV1 was inductive, but higher frequency for a smaller size. You might be able to run a 3 phase 60 hertz, but people like EP would be a better source of info on this one.

Losses might be 20% or so, just a guess. But safety is the big deal, so that might not be a big problem. Just imagining, but the charge station would be permanent, so the pads could come up from the street and self align. They bury power transformers, so this is not all that much different.

Rafael Seidl

I realize it's a prototype, but $1 million for a bus?


The paint job was expensive :)

Kim Fenske, JD, MST

From my research, I think that Design Line International is developing a better product for use with conventional diesel bus transit fleets.
For $500,000 to $550,000, the EcoSaver IV with a 30 KW turbine from Capstone can achieve nearly 10 MPG compared to about 4 MPG from a conventional diesel bus.

Design Line International Hybrid Bus [Charlotte, NC]:

Test run begins for hybrid bus

PIMP MY BUS - NY tests out MTA’s new green ride on 42nd Street
By David Freedlander -
October 12, 2007 -

AM New York

“Come on in. It still takes your money,” the bus driver said yesterday to confused would-be riders staring dumbfounded at the MTA’s latest rollout, a 35-
foot-long electric hybrid that’s on a two-month trial run up and down 42nd Street. As the bus took its inaugural rush-hour ride yesterday, giddy straphangers
waiting in the rain in Turtle Bay for the crosstown journey piled in like school kids on a field trip. “Oh, it feels like I’m going to the airport,” said one man
as he climbed aboard with his wife.

Indeed, the newest addition to the MTA’s fleet does feel like it’s about to drop riders off at the Rent-a-Car lot. With clean, blue cloth seats, silver poles without
straps and big tinted windows, the bus promises all the comforts New Yorkers have come not to expect on public transportation.

The bus is on a 60-day test run throughout the city. If all goes well, the MTA plans on purchasing a bunch of them. It gets eight to 10 miles per gallon on its
hybrid electric turbine engine. And without all that gaspowered churning of most buses, it’s pin-drop quiet, too. Quiet enough in fact to amplify every other cell
phone conversation being had on the bus. And quiet enough to hear the earrattling rap music pouring out of another rider’s headphones.


If they combine cycle those Capstone turbines they can get even more power and a quieter ride.


So, it looks like NG gas turbine hybrid buses with combined bottoming cycle using vapor turbines for over 10 mpg. We would have twice the mileage, half the fuel costs and no particulates. Sounds like a good combination. Big changes like this take a lot of effort, time and money but they are worth it and I think people in general would agree.

It is how you pay for it that makes a difference. It they come from highway funds paid for by gas taxes, that is one way. They could be financed so the rider fees pay some of the cost over time. If people pay $1 for a bus now, would they pay $2 for a cleaner, quieter and more fuel efficient bus? We do not know, but it is worth exploring.

Poor people riding the bus would have to pay more and that might be offset. However it is done, we can make it relatively painless and convenient. Before you know it all buses will be cleaner, quieter and more efficient. People like to see progress like that. It gives them faith and hope in the future. I know that sounds corny, but it is not.


$500,000 for a city bus?.. what is the normal cost of a bus? will it pay for itself in cost savings?

Eco Dude

It appears that San Diego didn't do their homework when claiming they are the first. In all fairness, San Diego MTS needs to remove the big letters on the top of their buses and cease claiming they are the first.

San Diego is about 8 years behind Denver.

RTD in Denver was the first and has been operating about three dozen CNG-electric hybrid buses on the 16th Street Mall:

pure electric car

Cars with hybrid electric engines, which are expected to account for 6. 5 percent of U. S. auto sales by 2012 according to a report by J. D. Power and Associates Automotive Forecasting Services, might not be available to used dealerships for some time. It typically takes two to five years for new cars to cycle through to resale points. But by that time, it might be too late for many area dealers.

billy bob

I gave my car to charity seven years ago. I use MTS exclusively. I have riden the CNG-Hybrid bus and I'm pleased to say that it was an "E" Ticket ride. The driver was enthusiastic about the added power and ease of control. I'm happy to see MTS looking to the future of energy conservation and cleaner air.

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