3.1 Surface Types
Sidewalks and shared use paths are the main types of pedestrian facilities that accommodate pedestrians. The surface material used for these facilities can have a significant effect on how and how often maintenance is performed. Of the hard surfaces, concrete is the most common surfacing type for sidewalks while asphalt is commonly used for shared use paths. However, there are communities that rely entirely on concrete surfacing for shared use paths and others that rely on asphalt for sidewalks. Furthermore, asphalt pavement is often used as a temporary pavement for patching concrete sidewalks.
Bricks and pavers are also used for pedestrian facilities. In some communities these materials are used to preserve a traditional material and appearance in a downtown or historic district. In some settings pavers are used to border concrete sidewalks. Although these materials tend to be very durable, they do have some unique maintenance issues which will be discussed in more detail later in this guide.
Surfaces can also be "soft" and composed of loose stone, compacted stone dust, or wood chips. Since wood chips are not considered a firm and stable material type under ADA and are very rarely found in the public right-of-way, they will not be discussed in this guide. Stone surfacing, especially crushed stone, is sometimes used for paths and sidewalks. It is more likely that stone or gravel will be used for sidewalks as a temporary fix before a more permanent surface material ultimately replaces it.
Here are the main types of sidewalk materials with a brief discussion of their maintenance characteristics.
Concrete is by far the most common form of pavement material used for sidewalks in the United States. It is a mixture of cement, water, aggregate, and sand. It is very durable and has a lifespan between 40 and 80 years. It is poured material and within 30 minutes or less a smooth finish is applied to the surface followed by a broom finish to help with traction. Because of its semi-fluid state when it is poured, it is an especially suitable material to use when there are multiple grades and cross slopes such at corners and curb ramps. New paving equipment in the past thirty years now enables the paving of long stretches of sidewalk without the use of form works. Finishing of the material requires a rapid pace when formless paving equipment is used because the concrete excreted by the machines is very stiff. Repair and replacement of sidewalks in concrete is still performed the same way it was 50 years ago, with forms and skilled finishers.
Asphalt is the most common material used for shared use paths in the United States. Asphalt is a less common material for sidewalks than concrete and typically has a significantly shorter life than concrete. However, the initial cost to install asphalt is typically significantly less than concrete. Asphalt consists of a petroleum base (tar) and aggregate. Asphalt must be compacted soon after it is applied to the surface preferably by heavy equipment. This makes it an attractive material for long stretches of sidewalk or path where a roller can be used. Asphalt can be used in other tighter settings, such as corners and curb ramps, where a hand mechanical tamper is used, but results typically do not match that of concrete. Often when asphalt is used for a path or sidewalk, concrete is used for the curb ramps. Asphalt is commonly used as a temporary patching and wedging material for concrete sidewalks.
3.1.3 Brick and Pavers
Brick is a traditional sidewalk material type that has been used for centuries in the United States. Bricks offer a high level of durability and can be reused and easily replaced. Bricks differ from concrete pavers in that they are made from formed clay which is then fired in a kiln. Bricks and concrete pavers are considered a "segmental material" because each paver is separate and is often not tied or bonded together the way a concrete slab is formed. Bricks have unique maintenance requirements and most communities consider bricks to be more costly and problematic to maintain than concrete. However, bricks and pavers can be individually replaced by experienced personnel with a smaller amount of effort than replacing entire sections of concrete sidewalks. Some communities use bricks and concrete pavers to highlight sidewalks in commercial areas or plazas. This approach often reduces maintenance costs and potential tripping hazards within the accessible path because the bricks are often laid over a solid concrete surface. Bricks are primarily rectangular and are manufactured in a wide range of colors. More recently, bricks and pavers have been manufactured and placed to create a more permeable surface and reduce surface runoff, but this requires more spacing between the materials.
Concrete pavers are also used for sidewalks and for sidewalk border applications. They consist of a mixture of cement, sand and water and function much like bricks when they are set in place as sidewalks or walkways. Like bricks, concrete pavers can be produced in many shapes, sizes and colors. They are durable, versatile and can be reused. Like all other sidewalk materials, attention to proper construction can reduce maintenance problems and costs in the future.
One of the shortcomings of bricks and pavers is that they can pop out of place and present a tripping hazard more easily than concrete or asphalt slab sidewalks. Both concrete and asphalt can also be horizontally cut or ground to mitigate tripping hazards, whereas bricks and pavers can be reused, but often have to be removed and repositioned so the base material can be modified to effectuate the leveling of the sidewalk.
Pavers made from recycled rubber and plastic have recently been introduced as a substitute for traditional sidewalk pavements. These pavers are modular systems similar to large concrete pavers. They are linked together with tabs. Communities have been attracted to these pavers for applications around trees where tree roots have caused concrete sidewalks to heave, although they can be used in most environments where sidewalks need to be placed in a relatively straight alignment. They are typically half the depth of concrete sidewalks and are more expensive than concrete.
3.2 Common Maintenance Issues
There are a number of specific maintenance issues that commonly occur for pedestrian facilities. These issues can be sorted into two broad groups – those that are directly related to the pedestrian facility infrastructure itself, such as sidewalk surfacing deficiencies, and those that relate to seasonal or day-to-day maintenance which require keeping the facility clean and free of nuisance materials. This involves removal of vegetation, snow, ice, sand, and other materials. An effective pedestrian facility maintenance program needs to address both sets of issues. The responsibility of day-to-day maintenance is often addressed by communities that then relegate the duties to adjacent property owners. This section will lay out the common types of issues associated with these two broad categories while later sections discuss inspection of these conditions, and a range of solutions to address them.
3.2.1 Infrastructure Issues Leading to Increased Maintenance
Infrastructure problems can be broadly categorized into two groups for sidewalks and paths – surfacing problems and structural problems. Both sets of problems cause maintenance issues. Most structural deficits will ultimately affect surface conditions, but there are certain surface conditions that are not caused by structural conditions.
Infrastructure deficiencies also exist for curb ramps, traffic signals, and crosswalks and are covered below.
Surfacing defects lead to a multitude of problems impacting maintenance. Certain defects cause concrete surfaces to crumble, including spalling, scaling and popouts. Poor curing and concrete quality or finishing techniques can all contribute to surface defects. Often these defects appear in the first several years after application. Minor defects may only affect appearance, but moderate to severe conditions will ultimately become a safety hazard and may significantly affect the usable life of the sidewalk. Often even minor defects will become moderate to major defects as more deterioration occurs over time because of the compromised surface.
Other surfacing deficits include raveling and cracking. Raveling is caused by high air voids in the material due to poor compaction or late season paving. Cracking can lead to series of problems for asphalt and concrete surfaces overtime. Cracking is caused by underlying structural defects below the surface.
The surface of bricks and concrete pavers occasionally exhibit surface problems. The quality of material is generally and consistently good because it is produced through a controlled and stable manufacturing process. The major maintenance problems with pavers and bricks usually are associated with displacement of the material itself and not the surface deterioration of the material.
Deformation forces causing structural problems for sidewalks and paths
The most common maintenance problems with hard surface materials result from structural conditions such as those caused by cracking, heaving, tilting, gaps (often at concrete joints), and sidewalk and path sections that either are depressed or raised. The Institute for Research in Construction of the Canadian National Research Council has undertaken an extensive study of concrete sidewalk issues and has defined the following four major deformation actions leading to structural damage to sidewalks. These same conditions cause failures in asphalt, as well as bricks and pavers. With the exception of cracking and gaps (which can be just a surface condition), all of the problems listed below are structural in nature and result from a series of structural failures from deformation forces described below. Many of the forces that cause damage to sidewalks are related to freeze and thaw action of the subbase. Photographs are provided which illustrate the potential aftermath of the forces at work.
|Rigid Body Uplift or Settlement|
|The tendency for a concrete sidewalk slab to rise, subside or tilt as a result of expansive native soil, frost action (freeze and thaw) or thermal expansion of the concrete slab. This could also be due to non-uniform compaction of the subgrade. Since asphalt has a high tensile strength compared to concrete, deformation around the uplift will occur often causing a crack or a mounding of the material, but typically not a break characterized by a rift or fault of the material as seen with concrete. Also commonly known as "vertical uplift" or "projecting edge."|
|Deformation resulting from tensile stresses during the shrinkage of underlying soil from decreasing moisture content.|
|The unequal movement of the slab as a result of the center of the sidewalk or path having a larger thaw settlement than at the edges, or native soil conditions where clays swell significantly at the edges. This leads to longitudinal cracking.
Note: The term sagging is commonly used to describe sidewalks that subside and entire slab or set of slabs drop below the initial grade. The forces that contribute to that are more accurately explained as tensile shrinkage described above.
|Raised or Heaved (Also referred to as hogging)|
|Unequal movement of the slab caused by frost heave or upward vertical movement due to swelling of clay native soils being greater at the center than at the edges. This will often lead to longitudinal cracking.
Raised pavements are also commonly caused by tree roots.
All of the above conditions will cause sidewalks and paths to deform, shift, heave, or buckle. When this occurs the surface of the material is affected and maintenance is necessary often involving spot repair of small or large sections of sidewalk or path.
Cracking and heaving are the two main results of the deformation forces at work. Cracking can occur in every direction of a surface when concrete is used. Since any given length of concrete will eventually crack, methods are used to control it. The main method of avoiding surface problems is to direct the cracking at joints which are placed in the concrete by either manually finishing them into the surface or making cuts with concrete saws as the surface is curing. Most of the maintenance problems stem from uncontrolled cracking, although sidewalk panels do heave at the joints. The ones mostly closely impacting sidewalks and paths are edge, alligator, and longitudinal cracking.
Alligator cracking is characterized as typically fine, longitudinal hairline cracks running parallel to each other with none or few interconnecting cracks. Longitudinal cracking occurs along the length of the sidewalk, usually in the middle third of the sidewalk, usually in the middle third of the sidewalk, and can extend through several expansion or control joints. Unlike alligator cracking, they are often larger. Transverse cracks occur across the width of the sidewalk due to non-uniform subgrade compaction, especially where sidewalks are subjected to high vehicle loads such as where driveways cross sidewalks.
Heaving of concrete sidewalk panels is a common problem that causes a significant number of tripping hazards. Heaving is also called vertical uplift, vertical displacement, faulting, and changes in level. Several of the deformation forces described above can lead to heaving. Because sidewalks are built with joints to control cracking, heaving most often occurs at these locations.
Other Pedestrian Facility Infrastructure Problems
Maintenance of pedestrian facilities is often associated with just sidewalks and sometimes paths, but other pedestrian facilities also incur problems which increase the need for maintenance. These facility types include curb ramps, crosswalk markings, pedestrian signals, and signage.
Curb ramps provide the transition between sidewalks and street crossings and allow pedestrians to reach street level at corners without stepping up and down at a curb. They are required by accessibility laws. Most of the same maintenance issues impacting sidewalks also impact curb ramps. All of the forces outlined above also deform curb ramps. All new curb ramps are required to have detectable warning fields which provide indications to people who are sight-impaired or blind to that they are about to enter a street. Although many different forms of detectable warnings have been used over the past 40 years, only truncated domes are now acceptable for use. They can be inserted into concrete as cast iron or stainless steel plates, applied as a glued-on material, or formed in place as the concrete ramp is finished. Each of these processes may lead to special maintenance problems. For example, the plate could become displaced causing a tripping hazard, adhesive may weaken for glued-on domes, or the concrete domes are likely to chip off when plowed. Additionally, the truncated domes must provide a color contrast to the ramp. Especially for formed-in-place domes, this requires an agency to periodically repaint the warning field. Chapter 7 of Designing Sidewalks and Trails for Access – Part II provides guidance for the current recommended design of curb ramps:
The most frequent maintenance problem with crosswalk markings is durability. Painted crosswalks have to be repainted several times a year based on the volume of traffic and the severity of the weather. Two other marking materials – epoxy and thermoplastics – are far more durable, but are significantly more expensive. In cold weather climates where salt and sand is used, the abrasiveness of the materials causes more rapid deterioration of the markings.
Another durability-related maintenance problem is the conspicuity or retroreflectivity of pavement markings. Glass beads or other reflective materials are added to marking materials to enhance nighttime conspicuity. When the markings wear, the reflective quality of the material is compromised.
Another area of concern with crosswalk markings is slipperiness of the markings. Manufacturers of these materials have taken steps to significantly improve the friction factor of their materials, but as the material wears, sometimes it becomes slicker causing a need for reapplication. Slippery markings make it necessary for municipalities to replace the markings sooner.
Based on the research conducted for this guide, communities consider their signals to be durable with the most serious maintenance problems being signal "take-downs" related to vehicle crashes. Other significant problems requiring maintenance include push buttons and signal heads that are malfunctioning. The replacement of signal heads with light emitting diodes (LEDs) has significantly reduced the need for replacement of light fixtures. LED lights last for approximately 100,000 hours, many times the life of incandescent bulbs. Filaments in incandescent bulbs burn out in approximately 10,000 hours. However, LEDs do not produce as much heat as incandescent bulbs and can become snowed over in blowing snow conditions.
Another set of hardware problems relates to the controller for the signal system. The controller is the device that manages the entire signal system for the intersection. Occasionally problems with the controller cause a pedestrian signal to malfunction.
Pedestrian signal systems have become more complex with the advent of Accessible Pedestrian Signals (APS). APS devices work with existing traffic signal controllers. Some APS devices require no additions to equipment in the signal controller cabinet for installation and operation depending on the type of equipment that is already installed.
APS devices will require additional wiring most often between the pedestrian signal head and pushbutton which on occasion have cause maintenance problems. However, most of the servicing needs are related to initial set-up including attention to pushbutton placement and alignment, and careful adjustment of sound volumes. APS devices offer considerable benefits to people who are disabled and most of the servicing needs can be resolved within the first several weeks or months of the initial installation.
Signs that act as wayfinding devices for pedestrians are no exception to this on-going maintenance problem. Unlike markings, signs have a much longer life – quite often more than 10 years. Several factors tend to lessen the life of signs – ultraviolet radiation and airborne pollutants can dramatically reduce the sign's useful life. Vandalism to signs is also a significant maintenance problem for signs in general. Signage replacement for pedestrian-related signage tends to take a lower priority to the maintenance of regulatory signs purposes (i.e. stop and yield signs).
3.2.2 Seasonal Maintenance
The conditions of sidewalks for safe, comfortable and accessible travel are influenced not only by infrastructure problems, but also by seasonal events such as snowfall, the accumulation of leaf debris and the overgrowth of vegetation. Maintenance activities to remove obstacles to safe walking are needed to keep sidewalks accessible and hazard-free year-round. Often these seasonal conditions are the cause of problems people most associate with maintenance or lack thereof.
Meeting the obligations to keep sidewalks accessible is reinforced by the Americans with Disabilities Act. The act requires that pedestrian facilities in the public right-of-way be accessible to people with disabilities. The federal act acknowledges that there may be isolated or temporary interruptions in accessibility, but otherwise walking surfaces must be kept clear of snow, debris, and any obstructions to a minimum passage width of 48 inches according to the proposed draft of the ADA Public Rights of Way Accessibility Guidelines (PROWAG).
Snow and Ice
The removal of snow and ice for many U.S. communities presents the most significant maintenance challenge they confront. Following a snowfall, snow and ice must be cleared from sidewalks, paths, curb ramps and crosswalks to provide safe and accessible passage for pedestrians. Common challenges exist to resumption of pedestrian travel after snowfalls. These include street plowing that pushes snow onto sidewalks or blocks crosswalks, clogged or obstructed drains that create puddles at curb ramps, patches of ice that create slip hazards, and failure to remove snow and ice completely from sidewalks. The need for winter maintenance is impacted by the amount of snowfall, the mean winter temperature, the amount and intensity of sunlight and a host of other issues in urban and suburban areas.
Expectations and preparedness for snow and ice removal range significantly based on the factors listed. The snowfall maps displayed in Figure 9 indicate where snow is most plentiful and for how many days on average snow remains on the ground, but these are just two factors in establishing the need for winter maintenance. It is possible for communities with relatively smaller amounts or drier (fluffier) snow, such as Fairbanks, Alaska, to have more significant maintenance problems because their average temperatures and sun penetration do not allow for the melting of snow and ice the same way it would occur in a place like Ohio. On the other hand, there are many southern U.S. communities that receive snow and ice so infrequently that they rely primarily on temperatures and sun to melt the maintenance problem away.
The likelihood of snow accumulations in the U.S. are better explained by climate type than how far north a community is located. Based on climate types, even cities in the most northern latitudes of the U.S. (not including Alaska) are prepared differently for snow and ice removal. For example, Seattle receives mostly rain during the winter months while Minneapolis (located further south) experiences snow. Minneapolis is better prepared for snow and ice removal than Seattle and the expectations among residents for prompt snow and ice removal are set higher than cities in more temperate regions. Where snowfalls and ice storms are infrequent and temperatures rebound quickly, snow and ice removal maintenance needs are low due to the temporary presence of the snow. Jurisdictions should still have policies and an action plan in place that addresses these key maintenance issues even though snow and ice are infrequent. Even within these more temperate areas, snow and ice accumulations during the months of December and January have a far greater chance of lingering than when inclement conditions occur in other months.
The maintenance issues with snow and ice are fairly straightforward. The accumulation of snow causes difficulty for people to move through it. More importantly, snow is obviously slippery and becomes even slipperier as the water content of the snow increases. As snow melts, it can refreeze as ice causing increased difficulties in removing it and greatly worsening conditions for pedestrian travel. It can also pool and then refreeze on sidewalks and in curb ramps causing unexpected and adverse conditions for pedestrians especially during nighttime hours when visibility is compromised. On their own, ice storms or ice accumulations are very serious for safe pedestrian movement. Rain that freezes on contact presents the most serious of all maintenance problems depending on the amount and duration of the accumulation. Adding complexity to how communities respond to these ice and conditions is the fact that often each one of the identified snow and ice accumulation problems calls for a different maintenance approach or technique and level of resources.
Curb ramps and median crossing islands present particular problems for accumulations and removal. They are often depressed and near gutters where water (and ice) can accumulate. Because of the presence of truncated domes in newly constructed ramps and crossing islands, removal of snow and ice is more of a problem than other detectable warning devices. Shoveling out curb ramps of snow is often the best way of controlling the snow and ice problem. However, very few communities have personnel that use shovels. If the curb ramps and median cut-throughs are not easily accessible by a skid steerer, pick-up truck, or snow plow, snow removal and ice control is often delayed if provided at all.
While the ADA PROWAG specify that sidewalks have 48 inches of clear passageway, different municipal ordinances have varying degrees of detail for how best to achieve a safe clear zone for pedestrians after a snowfall. For example, most ordinances specify that snow be removed from the edge of sidewalk to the edge of sidewalk, while others do not require this but specify the use of gravel, ash or salt on ice to prevent slip hazards. Some ordinances specify the maximum allowable height of snow banks and where snow cannot be piled to insure proper visibility of pedestrians. Some jurisdictions require snow removal from specific features such as fire hydrants, benches, driveways and curb ramps. Of the communities contacted, the most successful programs specify clearance expectations in detail by ordinance and in education materials provided to the public about their responsibilities.
Just as snow and ice can create outstanding problems for maintenance, so can extreme heat which is especially common in the southwest U.S. Most of the problems caused by extreme heat manifest themselves as serious structural problems and are presented in the first part of this chapter in 3.2.1. One of the most serious problems is when concrete expands and causes the sidewalks to buckle or heave. Asphalt is rarely used as walkways in these areas because of its problems with high air temperatures. However, asphalt used elsewhere leads to problems. For instance, the expansion of asphalt on streets at concrete curb ramps at higher trafficked intersections causes maintenance problems. When the asphalt gets heated up, heavier vehicles rounding the corner push it out and up which creates a 1" to 2" high asphalt lip next to the ramp. This causes problems for wheelchair users who cannot travel across the street and requires that maintenance crews to shave off the lips to make the transition smooth again.
Another problem in hot climates is associated with markings. Markings on newly paved streets can be degraded with vehicles tracking over them. Manufacturers recommend not putting the markings in place until a number of days to a week after new asphalt has been laid, but often this is not a viable option for busier streets. This is a more serious problem in hotter climates where a higher percentage of paving projects are completed and marked during a relatively long construction season much of it with high tempertautures.
Vegetation overgrowth and debris accumulation
Street trees and other plants adjacent to the sidewalk are a beneficial amenity for a variety of reasons including provision of shade, carbon dioxide reduction, increased property value, stormwater control and visual interest. However, vegetative growth encroaching upon sidewalks or paths is a serious condition that requires maintenance. Sightlines to driveways and intersections must also be maintained for pedestrian safety. In addition, the surface of the sidewalk must be kept free of debris. Many communities require adjacent property owners to keep a sidewalk free of vegetation or property owners are doing so on their own without any prodding. Here are the main problems with vegetation:
- Vegetation overhanging into the pedestrian path
- Vegetation growing at sidewalk level narrowing the effective width of the sidewalk and causing a tripping hazard
- Discarded vegetation building up on sidewalks, including leafs and branches
- Tree roots upheaving sidewalk sections
Vegetation that overhangs sidewalks and paths often presents serious and unexpected hazards to pedestrians. At its worse, this problem can completely close down a pedestrian facility. When that occurs, pedestrians will need to use adjacent streets presenting a safety issue. Vegetation growth at the sidewalk level can effectively narrow the width of a sidewalk or path. With asphalt, vegetation intrusion at the edges can break up the pavement. Narrowing of sidewalks and paths are an acute problem when the widths of the facilities are already at their minimum width.
In communities with street trees and large amounts of street vegetation, management of leaves and branches can be a significant seasonal factor. When leaves are left unintended on pedestrian facilities several problems arise: pedestrians cannot make out the pedestrian path below the leaves or are unable to spot tripping hazards or surface irregularities below the vegetation and the vegetation itself can become wet creating a slip and fall hazard.
Other debris can also form on sidewalks often carried by water or wind. This includes sand and other fine material. By the same token, many communities will use these materials to improve traction during ice or snow conditions. When these materials collect or reach a certain concentration they become a hazard when wet. Jurisdictions should have policy and action plans that address these key issues.
Other materials collecting on pedestrian facilities can also become problems. This includes rubbish that is simply discarded by people such as bottles and cans. Most communities sweep streets clean of debris, but do not extend that same level of care to pedestrian facilities. As with other maintenance practices, sweeping and dealing with the collection of debris is commonly made a responsibility of the adjacent property owners. The presence of debris on shared use paths presents the same issues with broken glass being an especially acute problem for bicyclists especially those with higher pressure tires.