CATS: Breaking friction-braking-barriers with regenerative braking

Number 28 in the Clean Air Technologies Series.

In the U.S. momentum is building regarding true high-speed rail implementation – principally in Texas and in the Washington, D.C. region. Meant by “true” high speed is operational velocities of 168 miles per hour or higher; typically 200 mph. Furthermore, surrounding the much anticipated fast-train system planned for California, that energy, in my opinion, has not waned in the least although, admittedly, there have been some speed bumps that have been encountered since state voters first approved Proposition 1A (the Safe, Reliable High-Speed Passenger Train Bond Act for the 21st Century) in Nov. 2008.

Compared to the shorter Texas – connecting Dallas and Houston – as well as with the magnetically levitated (maglev) D.C.-Baltimore high-speed train system proposals, the California endeavor will cover much more ground, 800 miles in all, linking San Francisco, Los Angeles, Sacramento and San Diego, the main spine of which is to traverse the expansive San Joaquin Valley and, in doing that, must also penetrate two formidable mountain barriers – the Tehachapi Range (in the south) and the Pacific Coast Range (in the northwest central part of the state) – in the process. By virtue of this, this high-speed rail endeavor is therefore placed in a category all its own.

If you recall – and even if you don’t – in “California high-speed rail looks to renewable resources for electricity supply,” I noted: “Considering the scope of the state project, the supply of electricity needed to power trains will be enormous. On the plus side in one sense is that full build-out of the statewide electrified rail network is not projected before 2033 which should allow more than enough time to beef up energy infrastructure to meet demand. More good news is that the trains, through their dynamic- or regenerative-braking-process capabilities will themselves in essence be electricity generators or power supplies. The energy produced from the regenerative braking process from say a braking train going downgrade, can be transferred to another train operating on level track or as well to another going upgrade or this electricity can even be fed to line- or wayside electricity storage systems for use at a later point in time.”

Yeah, but “How does regenerative braking work?” you might ask.

In my book: “The Departure Track: Railways of Tomorrow” I explain regenerative braking this way:

“As part of the regenerative braking process, electric motors effectively become generators. But there is far more to the braking process than just that.”

I went on to write: “Common to mass transit vehicles – and electric cars – regenerative braking as [CyberTran International, Inc. Chairman Neal B.] Sinclair explains: ‘is accomplished by letting the motors freely rotate with the axles. A circuit is closed through an electrical load, in this case a 3rd rail or battery pack. The closed circuit causes the motor magnetic field to rotate through the outer windings and the load. This exerts a braking action on the rotor, which is in turn transmitted to the wheels through the drive train. The whole drive train and motor becomes a generator, and the faster the vehicle is moving, the greater the braking force.’”1

The regenerative braking function can substitute for friction braking in some circumstances. As mentioned above, it has widespread application in the railway industry when it comes to train braking – electric and non-electric alike. In non-electric applications, such is known more familiarly as dynamic braking.

Friction braking, meanwhile, utilizes friction to slow and ultimately bring vehicles, etc. to a halt. In terms of friction braking, a common application, for example, is in the motor vehicle realm, where one can find wheel brakes equipped with calipers housing brake pads in between which sits a portion of a disc. With brakes applied, pressure is applied by the clamping calipers onto the flat brake disc surfaces. It is the created friction between the two surfaces that enables the braking action. During this process, some energy is given up and this is in the form of heat.

And speaking of friction braking and the Tehachapi Mountain Range for one, it is not uncommon for tractor-semi-trailer trucks descending California Highway 58 from the town of Tehachapi to just east of Edison in the southern San Joaquin Valley to have their friction-brake surfaces overheat thereby in the process releasing brake shoe smoke into the surrounding air.

So, in getting back to the high-speed rail application, if the California system gets built and trains traverse those same Tehachapi’s, count on regenerative braking to be a significant part of the operational platform. If so, not only will this reduce friction brake wear and tear, but usable electricity will be generated in the process thereby saving money from lower electricity bills, and air surrounding such trains will be kept cleaner, not to mention all-around better braking all as a result.

If this isn’t a win-win-win-win for California and the environment, then, truth be told, I don’t know what is!

Carbon ceramic disc brake
Carbon ceramic disc brake


  1. Alan Kandel, “The Departure Track: Railways of Tomorrow,” “Chapter 2: Section 2.1: Cyber Driven,” from the “Under the Hood” section: Braking with Electricity?, Dec. 8, 2013.

Image above: Dana60Cummins

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