The Oil Drum

20 comments on Transit-Oriented Redevelopment in New Orleans?

Comments can no longer be added to this story.

MikePH on January 14, 2006 - 9:54am

How energy-efficient is light rail? It's not too hard to figure out. The energy requirement is pretty well-documented. Dallas Area Rapid Transit's web site publishes their energy consumption. Light rail cars in the US would probably be called suburban trams in Europe because they are heavier and faster.

Power Requirements: 600-900 Volts DC. Requires 288 KWH per hour of operation. Dallas' cars weigh 107,000 pounds and are primarily used in high-speed rapid transit service. They are built by Kinkisharyo.

Houston's Harris County Metropolitan Transit Authority doesn't publish kwh information on their Siemens-Sacramento-built light rail cars. Houston's cars are four tons lighter, so let's assume they are roughly equivalent. Houston's operation is more similar to New Orleans in that the 7½-mile route is entirely street running with more frequent stops than Dallas.

On a weekday, Houston light rail carries about 32,000 riders on 160 round trips, or 320 one-way trips. It takes about 35 minutes for the cars to negotiate the densely-developed route, which is particularly congested through the Texas Medical Center. The cars make thirteen stops. This means that the average rail car carries close to 100 riders per trip. Let's assume the average passenger travels three miles. The cars are almost always used in single-unit operation, the exception being major events like football or baseball games. The cars seat between 64 and 72 persons, depending on whether the seats are raised to accommodate wheelchairs and bicycles. There is room for 98 standees. This means that they have 50% more capacity than Houston's large three-axle buses.

kwh used per one-way trip: 288 X 35 ÷ 60 = 168 kwh
passenger miles per per trip: 100 X 3 = 300
kwh per passenger mile: 168 ÷ 300 = 0.56

Looks pretty efficient to me.

Comments can no longer be added to this story.

ianbicking on January 15, 2006 - 4:17am

From my calculations, .56kWh = 1910 BTU, 1 gallon of gas = 125000 BTU, and so .56 kWh/mi is about the same as 65mpg (assuming 1 passenger in a car) or 60mpg (assuming the more average 1.1 passenger in a car). Which is a very efficient car -- somewhat better than hybrids, and I think there are some ultracompacts (not available in the US) that get close to that as well. Of course, my understanding is that there is substantial loss in electrical delivery, but whether that is more or less than gas I don't know. In electricity it is loss to resistence, largely, while in gas it is loss due to transportation and refinement. I'd be very interested to know how they compare to each other.

I also don't know what kind of systems they have in Houston and Dallas. Are these commuter lines? Commuter lines are notably quite efficient, because ridership is fairly high and consistent. Diesel commuter trains are very efficient as well. Systems that actually attempt to provide a real alternative to cars, and so have to run longer hours when ridership is less consistent, quickly lose their gain on cars in terms of energy per passenger mile.

Of course, to go the other way, the electricity doesn't usually come from fossil fuels (except coal which is relatively plentiful). So while electricity is not necessarily better than using fossil fuels directly, it is probably better in terms of peak oil, and maybe better in terms of CO2 production.

Comments can no longer be added to this story.

MikePH on January 15, 2006 - 7:23pm

Your response caused me to do some further research. I'm having problems with reconciling DART's kwh/per hour of operation of 288 with this information from Calgary Transit's website on their Siemens light rail cars, which are equivalent in weight, speed, passenger capacity to Dallas' and Houston's cars.

I'll be first to admit I am not skilled in energy calculations, but I checked your numbers out and they seem correct. Maybe you can help me with this and tell me if I am making a faulty assumption:

Calgary says their cars get "Power consumption (kwh per veh-km of operation) at: 3.23." That comes out to 5.38 kwh per mile. If this were applied Houston on a 7½-mile trip, they would use 40.375 kwh on a 35-minute trip or 69 kwh in an hour. That is a huge discrepancy to Dallas' claim of 288 kwh per hour of operation. If we used Calgary's numbers and applied them to Houston, with 300 passenger miles in the average 35-minute trip, the kwh cost per passenger mile would be only (40.375 / 300) .135 instead of 0.56. That would be equivalent to almost 250 mpg for a 1.1 passenger car.

The Calgary system and Dallas are more similar in that they are mostly reserved railway private rights of way at speeds between stations of 45 - 60 MPH. Dallas has two fairly long lines which together total 45 miles. For all intents these are electric railway commuter lines built to railroad standards but using light rail cars. Stations in Dallas average 1.25 miles apart. The stations are about ½ mile apart near the downtown Dallas area, but the distance stretches to up to 3½ miles in the northern suburbs. Here is a typical view of the Dallas system:

Houston is a street railway operation using light rail cars on a limited tramline concept, where stations are only ½-mile apart on the average and there are another dozen stops for motor vehicle traffic lights. Houston is very much like a streetcar line, other than the fact that the stops are about three times as far apart as those of a traditional streetcar:

Of the two systems, Dallas is much more extensive, starting operation in 1996 with about 20 miles and has grown to 45 miles since then. DART carries about 52,000 riders on a weekday, mostly between the suburbs and town. Vehicle frequencies on each of the two lines is about every 15 minutes on weekdays and every 20 minutes on weekends. There are many park and ride stations.

Houston, on the other hand, opened in 2004, and carries about 32,000 riders on a weekday. It's service is much more frequent, about every 6 minutes on weekdays and every 12 minutes on weekends. Houston's line primarily serves the Texas Medical Center, with 50,000 employees, and downtown, with 100,000 employees. There is only one park and ride station at the south end of the line.

Both Houston and Dallas offer free transfers to intersecting bus lines. Since Dallas is mostly elevated, subway and grade-separated rail right of ways, its speed is much higher than Houston's: 31 MPH versus 14 MPH, including stops. Because of the suburban character of Dallas' light rail versus Houston's urban one, the average passenger trip is much longer.

I just don't understand why Calgary's kwh per mile should yield such a lower energy cost than Dallas' number, since the vehicle weight and operating characteristics are so similar. Here is another source is closer to Calgary's specs, the American Public Transportation Association's 2003 Rail Fact Book:

POWER (miles/kwh)
Automated Guideway 0.16
Cable Car 0.13
Commuter Rail 0.11
Heavy Rail 0.15
Inclined Plane 0.07
Light Rail 0.13
Monorail (a) 0.32

If this is true, then, assuming Houston averages 100 passengers per trip, each traveling 3 miles, a fairly reasonable assumption based on their 32,000 ridership with 160 scheduled round trips, a 7½-mile run would consume 58 kwh, or, divided by 300 passenger miles, .19 kwh per passenger mile. This is higher than the .135 figure above, but much closer to than the .56 kwh per passenger mile I came up with yesterday based on Dallas' data. Your response along with Calgary Transit and APTA's figures makes me think that Dallas' kwh number is way to high.