How Street Sweepers Work

First, they take the broom and swish it left, then they swish it right -- okay, street sweepers haven't been men with brooms for more than a century. These days, they're drivers steering boxlike vehicles that look like a cross between a Zamboni machine and a dump truck.

There are a couple of types of street sweepers. There are those that clean the streets with brushes and those that clean with air. The basic function of any street sweeper is the same, though: The dirt has to be scrubbed from the road; it needs to be put in a little pile, and that pile needs to go into a bin until it can be disposed of properly.

Conventional street sweepers have jets under their trucks that shoot water onto the street's surface to keep flying dust particles to a minimum, while spinning brushes scrub the dirt free from the streets and gutters. A cylindrical brush under the truck sweeps the debris onto a conveyor belt that leads to a storage container. Sometimes, instead of the cylindrical brush, a vacuum-like mechanism will suck the debris into the container.

Regenerative air sweepers, on the other hand, have hydraulic systems that use air jets to churn up the dirt on the road, then swirl it toward the center of the truck. Negative pressure under the truck creates a vacuum that carries the dirt up into the receptacle at the truck's rear. Filters clean the air in the receptacle and reuse that air to loosen debris on the street, while water is sprayed to keep down the dust.

Some sweepers use spinning brushes instead of regenerative air or water to get the debris underneath the truck, where a vacuum moves it into the storage hopper. These models are usually smaller than the big street or highway sweepers, and they're used at industrial sites where cleaning up particulates is paramount.

All of this activity gives us a clue to why these trucks, small or large, are so darn noisy. First, they're usually powered by a heavy equipment-grade diesel motor. Second, there are either jets of water squirting away or a hydraulic system pumping air onto the street, not to mention the brushes spinning like crazy at about 4,000 revolutions per minute (rpm). There's a lot going on in a small package -- with very little sound dampening. Plus, they run when neighborhoods are quiet, either late at night or early in the morning, so we're more likely to notice the racket.

Let's move on to how these machines are used in our everyday lives, and what innovations we're seeing in the street sweeper's third century.

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We call them street sweepers, but the same mechanical surface cleaners can be customized to pick up just about any kind of debris from almost any surface. Sweepers can range in size from full trucks to portable, towable machines. The largest trucks are big enough and can go fast enough to drive on and clean up highways. They do have to slow down to do the actual cleaning, however; trying to sweep the highway at 70 mph (113 kph) just isn't going to work.

Little three-wheeled sweepers are far more maneuverable for cleaning between shelving units in a warehouse, for example, or any place where tight turns and limited space are an issue. There are sweepers built specifically for dumping collected debris in tall containers or trucks and sweepers that can empty their hoppers into low-lying containers. Some sweepers, like the Elgin GRV, are made specifically to remove de-icing solution from airport runways before it can seep into the groundwater.

Street sweepers do much more than just keep things clean. They're used to pick up trash, dirt, chemicals, motor oil and more that can contaminate the environment. If these potentially harmful substances are removed from the street, the construction site, or the parking lot before they reach storm drains, they are less likely to end up in rivers and lakes.

The United States government has already taken steps to combat this type of pollution. In 1987, the Environmental Protection Agency (EPA) enacted the PM-10 standard, which regulates the number of particles in the air that are 10 microns (.001 centimeters, or .0004 inches) or smaller. These particles are small enough to affect our health because of their ability to reach the lower regions of our lungs. Most street sweeper manufacturers have several machines that meet PM-10 removal standards, keeping our streets cleaner and our lungs clearer. Street sweeper makers need to stay on their toes, though -- the EPA is considering lowering the standard to PM-2.5, or regulating particle matter measuring 2.5 microns (.0001 inches) or less.

Some areas have policies regarding the amount of pollution the street sweepers themselves emit. For example, The South Coast Air Quality Management District in California -- which covers the smoggiest section of the U.S., including Orange County and most of Los Angeles -- has instituted Rule 1186, which requires any new large, outdoor street sweepers to run on alternative fuels. Many companies have machines that comply with Rule 1186 for sale across the country. They usually run on compressed natural gas (CNG), liquefied petroleum gas (LPG) or liquid natural gas (LNG).

All this technology isn't cheap: A conventional, mechanical, brush-using street sweeper costs in the neighborhood of $100,000. A vacuum-assisted model will cost $150,000 or more, with alternative fuel engines and pollution compliance driving up the dollar amount to more than $200,000. But that's a small price to pay to keep lungs (and gills) free and clear of contaminants.