How can a speed bump harvest electricity?

Car Safety Image Gallery A car passes over a large speed bump on Coto de Caza Drive in Coto de Caza, Calif. See more car safety pictures.
AP Photo/Reed Saxon

There was a time when debates surrounding speed bumps revolved around whether or not a community needed speed bumps to slow down drivers on a certain road. Safety was the key issue. Now, a new key issue is making its way into the discussion -- the question of whether or not speed bumps can actually harvest unused energy from a car.

Many energy discussions involving vehicles focus on how to reduce the fuel consumption or overall energy cost of operating that vehicle. Hybrid car technologies seem to focus on either reducing the amount of fuel a car uses or ways to create power (for the car) by implementing systems like regenerative braking. But using a vehicle to create power for an outside device hasn't received as much attention. So how might it work?


When a vehicle approaches a speed bump, most drivers press down on the brake pedal to slow the car down. The car's braking system expends energy that gets transferred to the brake pads and then into heat. It takes a lot of energy to slow or stop a car. In addition, the speed bump itself receives energy via the weight of the vehicle coming into contact with it.

Some engineers and technology companies want to harvest the energy that's being used to slow vehicles down at speed bumps, and utilize it to power things like traffic lights, freeway lights or even to send it to a power grid to be used by homes and business in the community. The idea is to gather up the energy that's being wasted when the vehicle goes over the speed bump.


Kinetic Plates

MotionPower generates electricity as a car drives over the device at the Four Seasons Hotel in Washington, DC.
Sam Hurd/National Press Club/New Energy Technologies, Inc.

So, now you know that a certain amount of energy is lost when a car approaches and drives over a speed bump; however, let's take a look at how some technology companies are developing solutions to harness that energy as its being spent. One speed bump design (that actually looks more like metal ramp) can extract the energy being used by a car slowing down and generate about 2,000 watts when the car is traveling at just 5 miles per hour (8 kilometers per hour) [source: Biello]. Some initial public testing took place at fast food restaurants where drivers would often slow down and move at low speeds anyway. The speed bump was wired to a light next to the store that would light up whenever a car was driving over top of the speed bump.

When a vehicle drives over these speed bumps or kinetic plates as they're sometimes referred to, a lever is thrown by the weight of the vehicle. The lever turns a flywheel that spins around and creates the energy. The flywheel works similar to a car's alternator -- it spins around and creates power to run electrical components on the vehicle. However, the electricity created by these speed bumps is instantaneous, and it must be immediately directed to a source to be used [source: Biello]. Engineers are currently working on ways to store the energy efficiently so that it can be used when it's needed most.


One company, New Energy Technologies, hopes to use variations of the speed bump on rumble strips at toll plazas, stop signs, freeway exit ramps, traffic lights and anywhere else vehicles are using energy to produce sizeable amounts of potential electricity. Although the technology seems like a useful endeavor, some are skeptical that the process could ever create enough power to be practical. Some even say that the system actually causes vehicles to use more energy to go over these types of speed bumps; meaning that any electricity created is done so through the vehicle burning more fuel to achieve the desired result [source: Chapa].

Although we don't see these speed bumps in regular use right now, many new types of technology are developing with the same idea. On the next page, we'll explore another technology attempting to extract energy from cars.


Other Electricity Harvesting Technologies

In the United Kingdom, some grocery stores have implemented the kinetic plate technology into their facilities Customers drive over the plates in the parking lot and the plates drive a generator that creates 30 kilowatts of power an hour [source: Chapa]. The store then uses the extra power to run their checkout equipment.

But aside from specially designed speed bumps that can extract energy from slow-moving vehicles, other technologies have recently been developed that are trying to harness wasted energy, although through different means.


In 2008, a group of students from the Massachusetts Institute of Technology developed a shock absorber that generates electricity each time a vehicle drives over bumps or potholes in the road. When a vehicle fitted with the shock absorbers goes over a bump, it forces fluid through a turbine attached to a generator. The spinning turbine and generator create electricity and then send it to a battery for storage. This system can increase a vehicle's fuel efficiency by up to 10 percent [source: Chandler].

The energy-producing shock absorbers work best on heavy-duty trucks, with a 6-shock truck being able to produce 1 kilowatt on average, per shock on normal road conditions [source: Chandler]. This amount of power would allow heavy vehicles to use power generated solely from the shock absorbers, without the help of an alternator, and could even produce enough power to run accessory devices.

This shock absorber technology differs from kinetic plates by taking the electricity produced by the vehicle and channeling it back into the vehicle, rather than to a fixed device. Sending the energy back to the vehicle may be a more efficient way of using the wasted energy, at least until energy extracted from speed bumps can be stored easily and transferred to devices or power management systems effectively.

For more information about harvesting energy from the road surface and other related topics, follow the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links

  • 60-Second Science
  • MIT News
  • New Energy Technologies Inc.

  • Biello, David. "Will a Speed Bump Power the Grid?" Scientific American. Sept. 3, 2009. (Jan. 19, 2010)
  • Chandler, David. L. "More power from bumps in the road." MIT News. Feb. 9, 2009. (Jan. 21, 2010)
  • Chapa, Jorge. "Sainsbury's New Kinetic Energy Powered Green Supermarket." Inhabitat. June 18, 2009. (Jan. 20, 2010)
  • New Energy Technologies Inc. (Jan. 20, 2010)