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Table of contents

• American Rural Highways by Thomas Radford
• American Rural Highways
• Catalog Record: American rural highways | HathiTrust Digital Library

These roads may be high-speed limited-access highways, arterials, or collectors, depending on the location and configuration of the roadway. The NHS includes urban and rural roads that serve a wide variety of transportation functions. The NHS comprises , miles of roads, 46, of which are interstate highways. The NHS serves major population centers, intermodal transportation facilities, international border crossings, and major travel destinations. It includes the interstate systems, other rural and urban principal arterials, highways that provide access to major intermodal transportation facilities, strategic highway network connectors, and the defense strategic highway network Figure Arterials consist of the interstate highway system, multilane limited-access freeways and expressways, and other road corridors that serve local areas; they also carry substantial statewide or interstate travel volumes.

American Rural Highways by Thomas Radford

This system accounts for approximately Collectors connect local streets and roads with arterials. They provide traffic circulation and land access among downtown city centers, industrial and commercial areas, and residential neighborhoods. Collectors provide lower speeds and less mobility for shorter distances than arterials. Travel represents vehicle miles traveled per year.

Source: FHWA The roads and streets functionally classified as local are all those not classified as part of the principal arterial, minor arterial, and collector system. Local roads and streets primarily provide access to adjacent land and are generally not maintained by a state highway agency. Local functional systems serve only The growth of suburbs, and the spread-out development patterns that come with it, has had a major influence on urban roadway patterns beginning in the s but particularly occurring after World War II.

The layout of the road system is not only a function of history and geography but is also linked to the local and regional development patterns. Layout patterns give roads different types of connectivity. The layout patterns and spacing among roads as well as their width number of lanes determine road density. There are several types of roadway layouts that are being used for designing roads.

These patterns can vary greatly from city to city but generally involve a rectangular grid, a hub-and-spoke layout, or a combination of the two. The road network in most cities across the United States is an out-growth of the Public Land Surveys and follows a rectangular grid pattern Figure Roads are orthogonal, alignment generally being along ordinal directions north-south or east-west.

Grid patterns generally have more total street length, blocks, intersections, and access points than other layouts. The grid pattern is typically intertwined with a mixed pattern of land use. Mixed land use was the dominant development style in American cities and towns in the early twentieth century and continued to be the primary pattern until the development of suburbs after World War II. A mixed land-use pattern can ease conges-. Source: MapQuest Reprinted with permission; copyright , MapQuest. The MapQuest. It may also reduce the total VMT if housing and services are intermixed.

However, it can also add unwanted through traffic on some residential streets Berkovitz In many locations, the hub-and-spoke pattern developed with the local growth pattern in the s and s. This system of roads comprises circular roads hubs, belts, and ring roads that go around a city center at various distances and separate roads spokes that go to the center of town Figure The circular roads are often used to route traffic around major urban areas, and the spokes are designed for commuter traffic.

Freeways and expressways interstate often form the circular hubs and major spokes in urban and suburban areas. The hub-and-spoke pattern is correlated with a type of land-use pattern that is designated as conventional land use. This pattern arose, in part, because of central urban planning and the increased importance of. Suburban areas grew in number and size to house families.

Residential areas are often built with cul de sacs and a small number of entry points to reduce the amount of pass-by traffic in residential neighborhoods Berkovitz In the conventional pattern of land use, each type of land use residential, commercial, retail, and industrial is separated from the others. Conventional land-use patterns result in more of a hub-and-spoke or circulatory pattern, with businesses in the center of town and residential areas surrounding the city. Some of the longest commutes in metropolitan regions are made by residents who live at the metropolitan edge and who work in downtown areas FHWA b.

In addition to roads and roadsides, the road system includes many engineering structures.

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These include concrete barriers, guardrails, noise barriers, bridges, culverts and pipes, and overpasses and underpasses. Each of these structures has a particular ecological effect. Rigid safety barriers separating lanes on roads are common, especially in urban areas. The most common type of these structures is called a Jersey barrier.

Some Jersey barriers are used for traffic separation on freeways and interstate highways, and many others are used only temporarily. Temporary units are used mainly to enhance safety in construction work zones. The height of Jersey barriers averages around 32 in. Rigid safety barriers are also commonly used longitudinally on major nonlimited-access highways to safely separate the two directions of traffic and preclude left turns and U-turns.

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There is current concern with barriers being formidable obstacles to small- and large-animal movement across highways. Barriers can block animals when they attempt to cross the highway, making them vulnerable to traffic mortality. Many different types of horizontal flexible and semirigid barriers, commonly known as guardrails, line the roadsides and medians of the roadway system. As with concrete barriers, guardrails are intended to constrain errant cars and trucks.



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Guardrails normally provide space beneath and above the rail that allows movement of wildlife. The principal difference between rigid safety barriers and guardrails is the amount deflection that will occur when they are hit. Right-of-way fences are used to keep people and animals from entering the berm, shoulders, and travel lanes of the highway. Many limited-access highways are lined with right-of-way fences, which enhance safety and reduce traffic mortality of large animals by reducing the crossing of animals.

The safest system is one with wide grassy medians and no hard barriers, where there is sufficient room for errant vehicles to recover before entering an opposing lane of traffic. No rigid barrier is needed if the median is approximately 50 ft or more in. Despite the safety offered by wide medians, there can be offsetting concerns because the median increases the width of the road right-of-way, including additional cost, availability of land in some locations, and compatibility of a wide right-of-way with nearby land uses.

American Rural Highways

Although wide medians in an additional loss of natural habitat, they may have less ecological impact than a narrow, paved median with a barrier or guardrail. Another advantage of a wide median is that the highway can be cost-effectively widened in the future with minimal disruption to traffic and to the adjacent properties, although if that happened, the ecological benefits of a wide median would be minimized or eliminated.

The decision to construct a new road over or under an existing facility is site-specific. Generally, minor roads should pass over major roads. This configuration takes advantage of off-ramp traffic being able to decelerate on the upgrade and the on-ramp traffic being able to accelerate on the downgrade Sharpe Although highways generally are constructed over waterways, the choice to span or pass under requires extensive analysis. Sometimes tunnels are built instead of bridges, as was the case with the 2. A tunnel was constructed instead of a bridge because of concerns that a bridge would tower over a historic site, Fort McHenry.

Often it is desirable to depress the major road to reduce noise impacts and improve aesthetics. Span lengths, angle of skew, soil conditions, drainage, and the maintenance and protection of traffic on the existing route all must be considered. Three-dimensional models of the alternatives are sometimes used to obtain informed public input into the decision.

Noise barriers are designed and built primarily to muffle highway traffic noise in residential areas, schools, playgrounds, and other sensitive. Noise barriers may also be retrofitted on highways to enhance the surrounding community. Almost all sound walls in the United States have been constructed since , and about two-thirds have been constructed of precast concrete and block. The other one-third of barriers are constructed of various materials, including wood, earth berm, and metal.



The average noise barrier height is 10 to 16 ft, although some are over 23 ft. Ongoing construction efforts to address deficient bridges offer a singular opportunity to address and mitigate important ecological issues. These issues are discussed in Chapter 3 ; mitigation of adverse effects of bridges and culverts is discussed in Chapter 4. The condition of bridges and other engineering structures is discussed later in this chapter.

Understanding the ownership and maintenance responsibilities for roadways is important for planning and managing the coordination of environmental and planning issues discussed in later chapters of this report. Local town, city, and county governments own and maintain The federal government owns only 3. Thus, coordination of transportation and environmental issues including ecological protection is often a state or local planning concern. Individual states own the remaining It reported that most of the existing road surfaces in the system are in good condition but that an aging set of bridges and other engineering structures are a challenge to the system.

The system is carrying higher. Many roads are approaching design capacity as congestion increases.

Catalog Record: American rural highways | HathiTrust Digital Library

These issues are discussed in the following sections. The use of urban roads continues to outpace the use of rural ones. The use and subsequent congestion are evident on both interstate and principal arterial roads. Although interstates play a key role in intercity connectivity, military support, and efficient long-distance travel, they also support local travel. Commercial uses moving freight within metropolitan areas , noncommercial uses providing access to airports and commuter travel , and individual uses are increasing the use of urban interstates. Reflecting the evolving expectations that state and local officials have for the interstates, growth in travel on their urban segments has been greater than on the rural portions, a trend that has continued since Figure ; FHWA b.

Travel per lane mile in rural areas has more than doubled since Urban interstate congestion is high in nearly half the states. As the ratio approaches the theoretical value of 1. Level of service LOS is another concept used in transportation work to describe different levels of congestion. LOS A is free-. Many sources suggest that travel is becoming more congested. However, off-peak travel has increased significantly in most major metropolitan highway systems in the past decade.

Urban interstates are the most crowded. Over the past several years, the overall condition of the pavement on the NHS and the interstate system has improved. In , on the basis of the international roughness index IRI , The IRI is an indicator of pavement performance, which uses an objective instrument-based rating system to measure the ride quality of a road. Pavements with an IRI of less than 95 have good or very good ride quality, those with an IRI of have an acceptable ride quality, and those with an IRI of more than have an unacceptable ride quality.

The NHS and the interstate system have a 6. FIGURE Percentage of vehicle miles traveled on urban freeways and principal arterials occurring under congested conditions from to Source: Schrank and Lomax Reprinted with permission; copyright , Texas Transportation Institute. Because of increasingly heavy use, most of the system requires substantial maintenance. Porous pavement is a newer technology for the primary highway system. Structurally, porous pavement has not proved to be as durable to heavy trucks and high traffic volumes as other road surfaces because of movement of water under the road, resulting in cracking.

Porous pavement also is a problem in states having to deal with snow removal because the sand and salts used in snow removal clog the openings.