Paving the Way: Power Walk

I magine a world in which your footsteps create the energy to power streetlights. This world exists, and you live in it.

U.K.-based Pavegen Systems has created slabs that convert kinetic energy from human footsteps into renewable electricity that can power streetlights, electric signs, outdoor lighting, advertisements and more. Surplus electricity generated by human footfall is stored in a battery within the slab itself and can be used to charge various low power devices, such as cell phones.

When stepped on, the flexible rubber surface of each Pavegen tile depresses ever so slightly, and the technology inside the slab converts this energy to electricity. To engage pedestrians in this renewable energy process, 5 percent of the electricity generated is used to light up the slab—a friendly reminder that technology is at work below the surface.

These Pavegen slabs are durable, built to withstand the outdoor elements and, of course, heavy foot traffic. The green surface layer is made of 97 percent recycled vehicle tires, and the remainder of the tile is made up of 60 percent recycled materials. By installing this technology in areas that pedestrians frequent—train and bus stations, busy sidewalks, crosswalks, shopping malls, school hallways and dance clubs—we will be able to harness the potential of the human footstep as an energy source.

Simon Langton Grammar School for Boys in the UK first installed Pavegen slabs in its corridors in 2010. By September 2012, Pavegen slabs are slated to become part of the terrain at the Westfield Stratford City Shopping Centre in London, one of the largest urban shopping centers in Europe.

As more spaces around the globe take advantage of renewable energy technology and products like those created by Pavegen, we are provided with an extraordinary opportunity— to reduce our carbon footprint with our actual footsteps.


Alleys Go Green with PicP

Green alleys, using permeable interlocking concrete pavement (PICP), require careful consideration during the design stages. Start with the end in mind, specifically calculating the amount of water that needs to be managed and where it is draining.

The first steps of the project are calculating runoff volumes from adjacent pavements and buildings, as well as timing how quickly water moves from roofs to the alley and into storm sewers.

In downtowns and highly urbanized areas, alley sewers receive roof runoff from downspouts and adjacent pavements. Green alleys provide a means to slow this flow, and in some cases, infiltrate a portion of the water into the soil subgrade. Slowing the flow can be done with berms and/or constricted outflow pipes that pool into catch basins before draining into the larger sewer system.

slow the flow

Berms are often required to slow flows when the subgrade slope exceeds 3 percent. Berms can consist of concrete, soil left in place, or lateral trenches dug across the width of the alley. The simplest berms consist of an open-graded base wrapped with two layers of geotextile, sitting atop the soil subgrade. Regardless of the material, the height of each berm depends on how much water needs to be detained and infiltrated (if soils are cooperative). Modeling flow is characterized by small ponds flowing one into the next. The outflow from one to the next can be via sheet flow, a knotch, or through a pipe (or pipes) penetrating the berms and aligning with the slope (i.e., oriented longitudinally).

Roof downspouts should drain water into the PICP base instead of its surface if there is an abundance of adjacent impervious surfaces. This reduces the risk of downspouts draining across impervious pavement and mobilizing sediment into the PICP openings. In addition, downspouts joining PICP base will flow longer in winter. In suburban settings, water from downspouts can run across vegetated areas, allowing for infiltration. Estimating the amount of runoff from the vegetated areas should assume the worst-case scenario for saturated soil infiltration rates.

modeling extremes

Depending on the geographic region, there could be extreme storms and rainfall depths that cannot be drained by the alley. When designing a green alley in these areas, the conditions that create flooding need to be modeled (i.e., the worst-case flooding scenario, including the depth and duration of standing water). If surface or subsurface bypass pipes or overland passages drain water from extreme rainfalls, all the better. If not, then the alley should be designed to minimize adjacent property damage in the event of deluge and flooding.

In downtowns and highly urbanized areas, alleys run next to building foundations. The foundations or sides of the alley will require covering by an impermeable liner to prevent water from infiltrating building foundations and basements, especially if the alley is designed as a detention/infiltration facility. This can be accomplished with restricted outflow pipes or perforated pipes along the soil subgrade that hold water until it deepens and then flows out of elevated drainpipes. In other instances where soil infiltration is negligible, there may be perforated drain pipes at the bottom of the alley that remove water almost immediately, which might obviate the need for liners against foundations.

Alleys often have utility poles that should not be surrounded with open-graded base. The utility poles should be moved or the open-graded base should be directed around them. They should be treated as structures; therefore, impermeable liners should be placed several feet away from their perimeter. Another option may be encasing the underground portion of the poles in concrete. Consultation with an engineer from the company that owns the poles is essential. The depth of the poles and distance of undisturbed soil around each should be discussed.

Alleys may have some distance between the back of the buildings and the alley surface. This space can be lawn, a separate garage or outbuilding, or gravel or dirt parking spaces. To reduce the risk of sedimentation and clogging, consider paving these surfaces with permeables as well. PICP alleys require curbs, which occasionally can be sloped to block or divert water and sediment flows from adjacent parking spaces away from the permeable surface.

Alley maintenance is almost non-existent in many cities because surface cleaning, snow removal and deicing are not budgeted. All permeable pavements for green alleys will require regular surface vacuuming. Because some sewer authorities have installed green alleys, they have assumed surface cleaning, especially if the city doesn’t maintain alleys. Surface cleaning is essential, because incidental litter from trash, leaves and grass clippings can accumulate on alley surfaces. For whomever maintains the alleys within a city, green alleys should be included in computerized pavement or sewer management systems.

transforming character

Underground utilities generally are not an issue, as long as they consist of waterproof piping and are deep enough to survive compaction of stone base materials over them without damage. Keep in mind that some utility lines are encased in open-graded stone, and that stone can be a pathway for water if adjacent to a permeable pavement base. In such cases, the flow of water onto the stone around a pipe exposed at the side of a permeable pavement excavation will need to be stopped with low-strength concrete fill.

When alleys go green with PICP, they can be paved with light colored paving units, which can enhance night lighting and help reduce urban temperatures. Alleys in older cities are often made of stones or bricks, and PICP can take on the appearance of either surface, thereby preserving and reinforcing the paving tradition and design context of these older cities.

The transformation from an unsightly alley in a backyard to a clean, well-kept space may increase private property values and earn money for the city in the form of higher property taxes. And for cities with combined sewers, green alleys are another effective tool in the green roads/green infrastructure toolbox that can reduce combined sewer overflows with stormwater detention and infiltration.

Combined sewers or not, green alleys can increase a neighborhood’s character and provide much-needed public spaces in dense urban areas.


Rethinking A Lot

One of the standing jokes about shoppers is their urge to park as close to the store as possible, even if this requires driving around the lot for a few extra minutes looking for that premium parking space. Once the car is parked, the parking lot is merely an ‘in-between’ space to get through as quickly as possible to reach one’s destination.

A recent book, Rethinking A Lot – The Design and Culture of Parking by Eran Ben-Joseph, tells us what we already know about supersized, mostly vacant parking lots: They erode urban visual, environmental and social quality. A shocking statistic, however, is Ben-Joseph’s estimate of the total area of parking in the U.S. at 500 million spaces.That’s about 3,590 square miles (929,805 ha)—an area slightly larger than Puerto Rico.

Ben-Joseph redeems parking lots used for community or social functions, such as farmers’ markets, tailgating and traveling carnivals. He recognizes that parking lots present significant opportunities for combining social spaces and economic gain. Parking lots with environmental benefits, such as permeable surfaces, receive recognition as well. Installing solar panels and parking cars under them might make sense as solar cell costs decrease. Imagine a garage structure built from solar panels paid for by the very electricity that is generated and sold back to the power company.

From the industry perspective, a parking pavement area more or less the size of Puerto Rico will need to be replaced in the next 50 years. With tightening stormwater regulations, some lots will be retrofitted with permeable pavement. Even if a modest 3 percent of this massive parking area is converted to permeable interlocking concrete pavement (PICP), that’s two square miles or 55.7 million sf (518 ha) per year of PICP. We are rethinking a lot.

Speaking of rethinking, you’ve probably noticed the new look and feel to this magazine. You are holding the first of the next generation. The name change from Interlocking Concrete Pavement Magazine to Interlock Design includes layout and content enhancements. We continue to present quality information on commercial and municipal interlocking pavement projects for design professionals, contractors and project owners. Advertising will soon include outstanding products from paver manufacturers and allied concrete product producers. We invite readers to send successful projects to feature in future issues. From our first publication in February 1994, to this new one, and those to come, we aim to present you with many new ideas and reasons to rethink a lot.


Moving Pavement

A few California developers and local agencies are already using PICP. Caltrans development of specs and a design guide should support increased PICP use.

The California Department of Transportation (Caltrans) is the first state transportation agency to develop a specification and design guide for permeable interlocking concrete pavement (PICP). Typically, state governments rely on their stormwater departments to develop such information. Stormwater departments reside within agencies that have “environment,” “water” or “conservation” in their titles. Examples include permeable pavement guidelines from the Virginia Department of Conservation and Recreation, North Carolina Department of

Environment and Natural Resources, and the Rhode Island Department of Environmental Management, to name a few.

plainly speaking

Caltrans has developed a draft specification for PICP and pervious concrete that will be released in the coming months. This was done with support by the Concrete Masonry Association of California and Nevada (CMACN), the California Nevada Cement Association (CNCA) and the Interlocking Concrete Pavement Institute. All permeable pavement specifications are written in the Caltrans “plain language” style and initially will be “non-standard special provision specs” used for non-highway facilities. This specification status allows for greater flexibility in modifying specs during construction. In addition, this status enables Caltrans to initiate permeable pavement projects and then return to the specifications a year or two later with revisions drawn from construction experience. Based on successful experience and further

technical review within Caltrans, the specifications eventually should be a permanent entry in the Caltrans book, Standard Specifications, periodically updated by the agency.


The draft PICP specification uses the existing structure of Standard Specifications, placing PICP in Division V Surfacing and Pavements, Section 40 Concrete Pavements. PICP is situated in a subsection labeled 40-9 Permeable Interlocking Concrete Pavement. This section covers the concrete pavers, which must conform to ASTM C936, Standard Specification for Solid Concrete Interlocking Paving Units, as well as the permeable jointing and bedding stone. Jointing stone sizes conform to ASTM No. 8, 89 or 9 stone, and selection is based on the maximum joint width between pavers. Bedding stone is consistently No. 8 stone. Other changes to Caltrans specs include Section 26 Aggregate Bases, which introduces a new Class 4 base with gradation, cleanness and durability requirements per Caltrans California Test methods, as well as a minimum 30 percent void space. Changes were also made to Section 19 Earthwork to allow for lower compacted soil densities than that required for conventional pavement.

One requirement of the Caltrans PICP specification is that the job foreman holds a certificate of completion in the Interlocking Concrete Pavement Institute PICP Technician Course. This requirement includes qualified construction personnel on job sites. Also, Caltrans acceptance of the completed PICP includes surface infiltration testing using ASTM C1701, Standard Test Method for Infiltration Rate of In Place Pervious Concrete. The minimum construction acceptance infiltration rate is 100 in./hr (250 cm/hr). This infiltration rate can be consistently attained regardless of the percentage of paver open surface area or the jointing materials.


All permeable pavement projects are subject to review and approval by the Caltrans Office of Stormwater Management-Design, and structural designs are reviewed and approved by Caltrans Pavements Program. The hydrologic design criteria require capturing 85 percent of all storms, also known as the water quality volume (WQV) capture depth. The emphasis is on treatment in managing stormwater across most of California rather than on volume reduction due to low rainfall. This WQV calculation method is well established within Caltrans and by the California Stormwater Quality Association. The most effective means of treatment—by reducing volumes—is accomplished with permeable pavement.


Storms with higher depths can be managed by the permeable pavement if required. The maximum infiltration time is 48 hours and the minimum acceptable soil infiltration rate is 0.01 in./hr (0.25 mm/hr). This minimum rate enables permeable pavements to be used in compacted soils, including some clay soils, resulting in about ½ in. (13 mm) of infiltrated water over 48 hours.

Caltrans structural design is essentially for cars and limited truck use on low-speed areas such as parking lots. The design approach is conservative and does not account for experience in other states with heavier loads/repetitions. The CMACN, CNCA and the ICPI Foundation for Education and Research are preparing to conduct PICP structural testing at the University of California Pavement Research Center in Davis, which will provide design charts to Caltrans for PICP base thicknesses. This study is slated to start before the end of 2012 and has wider implications on structural design for state and local agencies, as well as designers and industry outside California.

As with many states, numerous California city and county agencies reference state highway specifications for pavement materials and construction practices in their development standards. The inclusion of permeable pavements in Caltrans’ provisional specification sends a credible message to city and county engineering departments and further supports permeable pavement application beyond limited use expected by Caltrans.


Test News Item

Here is the body for the test news item


About Interlock Design

About Interlock Design:

Interlock Design is the official magazine of the Interlocking Concrete Pavement Institute (ICPI). Featuring the latest news, applications, case studies and information about the segmental concrete pavement industry, Interlock Design is the trusted source for over 24,000 design professionals, contractors and industry leaders.


About ICPI:

The Interlocking Concrete Pavement Institute (ICPI), founded in 1993, is the North American trade association representing the interlocking concrete paving industry. 

ICPI is considered by peer associations around the world as the leader in development and dissemination of technical information for design professionals and contractors. Our leadership position is due to years of commitment and energy from more than 1,100 members. ICPI engages in a broad range of technical, marketing, educational, government relations and communications activities.

Membership consists of interlocking paver manufacturers, design professionals, paver installation contractors and suppliers of products and services related to the industry. ICPI offers a variety of services to its members through its vast library of technical publications, online design idea galleries, publications, paver installer certification programs and the industry’s only dedicated magazine, Interlock Design.


Green Alleys

Converting dank and dirty alleyways into green infrastructure that helps cities reduce stormwater runoff is no easy task. But more cities across the country are stepping up to the challenge. The green alley movement, which began in Chicago in 2006, has spread to cities including Los Angeles, D.C., Philadelphia, Baltimore, Seattle, Boston, Richmond and more.


For several reasons: According to Chicago’s landmark and now definitive Green Alley Handbook, green alleys “showcase innovative, environmental technologies to help manage stormwater, reduce heat in urban areas, promote recycling and conserve energy.”

Retrofitting alleys with permeable pavement slows the flow of water and in some case enables water to infiltrate into the soil below rather than overflow combined sanitary and storm sewers that can lead to flooding of nearby property, the handbook states.

Additionally, converted alleys can be used by residents and adjacent property owners as outdoor space for urban gardens, sidewalk cafes and farmers’ markets. So it’s good for the earth and good for the neighborhood.


In Chicago, former mayor Richard M. Daley launched the Green Alley Program six years ago as part of his environmental and beautification campaign. Because many of the city’s 1,900 miles (3000 km) of alleys were originally built without a connection to the city’s combined sewer and stormwater system, flooding is a common problem. So the goal became to resurface the city’s alleys—traditionally used for trash pick-up and garage access—with permeable materials that allow water to infiltrate into the ground instead of leaving behind pools of stagnant water or having polluted water flow into Lake Michigan.

Today, under the guidance of Janet Attarian, AIA, Project Director for Chicago’s Department of Transportation, more than 100 green alleys have been installed throughout the city. More are installed annually. And they’re working.

Chicago’s green infrastructure, including its green alleys, diverted about 70 million gallons of stormwater from treatment facilities in 2009, according to a study co-authored by the Society of Landscape Architects, American Rivers, the Water Environment Federation and ECONorthwest.

Other cities have followed suit.

Richmond, Virginia

Like Chicago, Richmond, Va., has a combined sewer system and a need to address quantity and quality of stormwater runoff.

Between 2008 and 2009, the City worked to secure grants, get approval from the planning commission and the urban design committee, plan the design, coordinate contractors and specify materials for its first green alley project on 5th Street downtown.

Construction kicked off early in 2010, took three months to complete and cost about $15/sf, says Michelle Virts, Deputy Director of The City of Richmond.

“The first alley took about a year to get going, but the following alleys have been much faster,” she says. “Now that we have a process in place, things will go much more quickly.”

The alleys that followed—made with permeable interlocking concrete pavers—include two residential alleys on St. Christopher’s Lane and Monument Avenue, and a second downtown alley on 12th Street that was completed this summer.

So why these particular alleys?

“We picked our worst alleys,” Virts says. “Those that were filled with lots of trash cans, had bad flooding, and heavy pedestrian traffic. We also chose the two neighborhood alleys to see how the residential use of the space would impact the success of the alley.”

So far, the response from residents has been nothing but positive—they not only appreciate the improved functionality of the alleys, but the look and feel as well.

By choosing pavers that replicate the look of old cobblestone streets, Virts says, “We’ve been able to maintain the historical integrity of our alleys.”

Virts says the City is currently working on the planning and design of two more residential alleys, construction of which she’s hoping will be completed by the end of the year.

“We’ll continue working with the Department of Public Works, which maintains our alleys, to identify alleys that need to be retrofitted,” she says. “It’s still considered a pilot project, but we would like to incorporate these into our budget at some point soon.”

Los Angeles, California

Due to budget cutbacks, Los Angeles struggled to complete its first green alley, but it’s now officially open for business.

The East Cahuenga Pedestrian Alley (nicknamed the EaCa Alley) located in the Hollywood Entertainment District (HED) opened to the public in February this year, but the idea for the massive renovation was first introduced by City Council President Eric Garcetti in the fall of 2008. Garcetti’s motion to make a pedestrian mall out of the run-down alley claimed that it had been illegally gated and used privately by nearby businesses, denying access to the public.

Carl De La Fuente, Project Manager for the City of Los Angeles, says that not only was the alley being used improperly, it was disgusting.

“It looked like a war zone,” he says. “It was basically a trash dump filled with potholes and stagnant water, so the effort just to clean it up was huge.”

The project, which used cutting-edge filtration and permeable interlocking concrete paving systems, cost $790,000 and took the City, working in intermittent stages, just under a year to complete. The space is now home to weekend artists’ and farmers’ markets, sculptures, landscaping, lighting, and outdoor dining areas set up by several restaurants located along the alley.

But green alleys in Los Angeles can do more than support neighborhood commerce, they can save the city money.

The Council for Watershed Health’s Los Angeles Basin Water Augmentation study found that the Los Angeles basin relies on imported water for two-thirds of its water supply. By recharging the city’s groundwater resources through infiltration-based practices (including permeable pavers), the area could recharge 384,000 acre-feet per year. This equates to a dollar value of $310 million saved from the cost of importing and pumping from other sources outside the region.

In the 1920s, less than 5 percent of precipitation in the Los Angeles region flowed to the sea. Today, it’s over 50 percent, and with it flows many pollutants that cause beach closures. When beaches close, tourism drops; when tourism drops, it becomes a loss of revenues to Los Angeles and the surrounding cities.

So Los Angeles has begun a green streets program to encourage rainfall to return to aquifers while improving the urban milieu. There are 26 alleys in the HED all of which are slated for assessment, an effort that began in 2009 and will run through December 2018. As for which one the City tackles next, De La Fuente says there are seven alleys in particular that are in the greatest need of repair, but there are no plans yet in the making.

“After the titanic effort getting the first one completed, all the others will seem easy,” he says.

Washington, D.C.

Washington, D.C.-based Meredith Upchurch, Green Alley Project Manager and LID Team Lead, Stormwater Management Branch, Infrastructure Project Management Administration, would agree that getting the first alley up is the toughest. From the award of funding in 2009 until construction completion, D.C.’s initial three green alley projects took two and a half years to complete, including site selection, design, and construction.

“The biggest challenges were choosing locations and deciding what level of design is needed for the sites,” she says. “For the initial three sites, we chose alleys in poor condition that were scheduled for repaving or were unpaved and had drainage problems.”

Construction on another green alley in the northeast area of the city in the Anacostia watershed—the site of the first three alleys—is slated for later this summer, and seven more alleys in the Rock Creek and Potomac watersheds will start construction in the fall. All of the upcoming alleys will be installed with permeable concrete pavers, pervious concrete and porous asphalt.

Alleys make up almost 2 percent of the total land area in D.C., so addressing runoff from all paved areas to reduce stormwater volume and improve water quality is a primary concern, Upchurch says.

“It just makes sense to do a green alley when we are making needed alley improvements,” she adds.

Not only can a city save money on the treatment and conveyance of water, it may also prevent the city from being fined by the Environmental Protection Agency for exceeding pollutant levels, as directed by the National Pollutant Discharge Elimination System permit program.

While the initial effort to launch a green alley program may be exhausting, the long-term benefits are well worth it.


Contact Us

Jessica Chase, CAE

Publishing Director


David R. Smith

Managing Editor


Trey Higgens



ICPI website



Click banner below to download the 2017 Interlock Design Media Kit.