Interstate Highway standards

Last updated

I-blank.svg
I-blank wide.svg
Blank markers used for one- and two-digit (left) or three-digit and suffixed (right) Interstates

Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication A Policy on Design Standards: Interstate System. For a certain highway to be considered an Interstate Highway, it must meet these construction requirements or obtain a waiver from the Federal Highway Administration.

Contents

Standards

Standardization helps keep road design consistent, such that drivers can learn the consistent features and drive accordingly. [1] [2] Standardization can therefore decrease accidents and increase driver safety. [3]

An Interstate Highway under construction (I-196), with both directions of traffic moved to one side of the roadway Interstate 196 Construction.jpg
An Interstate Highway under construction (I-196), with both directions of traffic moved to one side of the roadway
I-94 in Michigan, showing examples of non-interchange overpass signage in median, upcoming exit signage on right shoulder, a pre-1960 overpass with height restriction signage, newly installed cable median barrier, and parallel grooved pavement with shoulder rumble strips Non Interchange Signage with Mileage Signage.jpg
I-94 in Michigan, showing examples of non-interchange overpass signage in median, upcoming exit signage on right shoulder, a pre-1960 overpass with height restriction signage, newly installed cable median barrier, and parallel grooved pavement with shoulder rumble strips
An Interstate Highway bridge with an asphalt overlay Interstate 25 Highway Bridge with Asphalt Overlay.jpg
An Interstate Highway bridge with an asphalt overlay
The Bobby Hopper Tunnel on I-49 in Arkansas was built with a 25 ft (7.6 m) height total clearance, leaving plenty of room for lighting and signs hanging from the ceiling and still exceeding the 16 ft (4.9 m) minimum for rural highways. Side clearances were reduced from the recommended 44.0 ft (13.4 m) to 38.0 ft (11.6 m) due to cost concerns. Approaching Bobby Hopper Tunnel.jpg
The Bobby Hopper Tunnel on I-49 in Arkansas was built with a 25 ft (7.6 m) height total clearance, leaving plenty of room for lighting and signs hanging from the ceiling and still exceeding the 16 ft (4.9 m) minimum for rural highways. Side clearances were reduced from the recommended 44.0 ft (13.4 m) to 38.0 ft (11.6 m) due to cost concerns.

These standards are, as of May 2023:

Exceptions

A narrow, older "grandfathered" section of I-94/I-69 after entering Michigan from Sarnia, Ontario. This section has since been reconstructed to modern standards. Older Style Narrow Interstate Highway 94 69.jpg
A narrow, older "grandfathered" section of I-94/I-69 after entering Michigan from Sarnia, Ontario. This section has since been reconstructed to modern standards.

Interstate standards have changed over the years, which has resulted in many older roads not conforming to current standards and an increase of roads not being built to these standards because to do so would be too costly or environmentally unsound.

Some roads were grandfathered into the system. Most of these were toll roads that were built before the Interstate system came into existence or were under construction at the time President Dwight D. Eisenhower signed the Federal-Aid Highway Act of 1956. One example is the Pennsylvania Turnpike, which originally had a very narrow median that later required the installation of a steel guardrail and later a Jersey barrier due to heavy traffic loads.[ citation needed ] The Kansas Turnpike had a 20-foot (6.1 m) depressed median (16 feet [4.9 m] narrower than the Interstate minimum) along its entire 236-mile (380 km) length from its opening in 1956 through the mid-1980s when Jersey barriers were installed.[ citation needed ]

Interstate 35E through Saint Paul, Minnesota is an example of a freeway that was not grandfathered into the system but is nonetheless an exception to standards. Initially designed in the 1960s, but not opened until 1990, the freeway has a speed limit of 45 mph (72 km/h), and does not allow vehicles weighing over 9,000 pounds (4,100 kg) gross vehicle weight (GVW). This is due to political opposition from surrounding homeowners in local neighborhoods, which greatly delayed and modified the project. [6] Interstate 670, a spur of Interstate 70, also fails to reach the 50 mile per hour minimum and instead passes through Downtown Kansas City, Missouri at 45 miles per hour. [7]

Interstate 75 on the Mackinac Bridge between St. Ignace and Mackinaw City, Michigan, is undivided. The bridge was designed before the start of the Interstate Highway System, and it was grandfathered into the system. [8]

Interstate 93 super two through Franconia Notch, New Hampshire I-93 Franconia Notch.jpg
Interstate 93 super two through Franconia Notch, New Hampshire

Interstate 93 through Franconia Notch, New Hampshire is also a notable exception, being a super two parkway with a speed limit of 45 mph (72 km/h).

All of the unsigned Interstates in Alaska and Puerto Rico are exempt from Interstate Highway standards and are instead, per Title 23, Chapter 1, Section 103 of the U.S. Code, "designed in accordance with such geometric and construction standards as are adequate for current and probable future traffic demands and the needs of the locality of the highway". [9]

Related Research Articles

<span class="mw-page-title-main">Shoulder (road)</span> Reserve lane by the verge of a roadway

A shoulder, hard shoulder or breakdown lane is an emergency stopping lane by the verge on the outer side of a road or motorway. Many wider freeways, or expressways elsewhere have shoulders on both sides of each directional carriageway—in the median, as well as at the outer edges of the road, for additional safety. Shoulders are not intended for use by through traffic, although there are exceptions.

<span class="mw-page-title-main">Dual carriageway</span> Type of road

A dual carriageway (BrE) or a divided highway (AmE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways.

<span class="mw-page-title-main">Lane</span> Part of a carriageway meant for a single line of vehicles

In road transport, a lane is part of a roadway that is designated to be used by a single line of vehicles to control and guide drivers and reduce traffic conflicts. Most public roads (highways) have at least two lanes, one for traffic in each direction, separated by lane markings. On multilane roadways and busier two-lane roads, lanes are designated with road surface markings. Major highways often have two multi-lane roadways separated by a median.

<span class="mw-page-title-main">Rumble strip</span> Road safety feature

Rumble strips are a traffic calming feature to alert inattentive drivers of potential danger, by causing a tactile fuzzy vibration and audible rumbling transmitted through the wheels into the vehicle interior. A rumble strip is applied along the direction of travel following an edgeline or centerline, to alert drivers when they drift from their lane. Rumble strips may also be installed in a series across the direction of travel, to warn drivers of a stop or slowdown ahead, or of an approaching danger spot.

<span class="mw-page-title-main">Median strip</span> Reserved area that separates opposing lanes of traffic on divided roadways

A median strip, central reservation, roadway median, or traffic median is the reserved area that separates opposing lanes of traffic on divided roadways such as divided highways, dual carriageways, freeways, and motorways. The term also applies to divided roadways other than highways, including some major streets in urban or suburban areas. The reserved area may simply be paved, but commonly it is adapted to other functions; for example, it may accommodate decorative landscaping, trees, a median barrier, or railway, rapid transit, light rail, or streetcar lines.

<span class="mw-page-title-main">Limited-access road</span> High-speed road with many characteristics of a controlled-access highway (freeway or motorway)

A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, and partial controlled-access highway, is a highway or arterial road for high-speed traffic which has many or most characteristics of a controlled-access highway, including limited or no access to adjacent property, some degree of separation of opposing traffic flow, use of grade separated interchanges to some extent, prohibition of slow modes of transport, such as bicycles, horse-drawn vehicles or ridden horses, or self-propelled agricultural machines; and very few or no intersecting cross-streets or level crossings. The degree of isolation from local traffic allowed varies between countries and regions. The precise definition of these terms varies by jurisdiction.

<span class="mw-page-title-main">Elevated highway</span>

An elevated highway is a controlled-access highway that is raised above grade for its entire length. Elevation is usually constructed as viaducts, typically a long pier bridge. Technically, the entire highway is a single bridge.

A wide outside lane (WOL) or wide curb lane (WCL) is an outermost lane of a roadway that is wide enough to be safely shared side by side by a bicycle and a wider motor vehicle at the same time. The terms are used by cyclists and bicycle transportation planners in the United States. Generally, the minimum-width standard for a WOL in the US is 14 feet. A wide outside through lane (WOTL) is a WOL that is intended for use by through traffic.

<span class="mw-page-title-main">Bicycle transportation planning and engineering</span>

Bicycle transportation planning and engineering are the disciplines related to transportation engineering and transportation planning concerning bicycles as a mode of transport and the concomitant study, design and implementation of cycling infrastructure. It includes the study and design of dedicated transport facilities for cyclists as well as mixed-mode environments and how both of these examples can be made to work safely. In jurisdictions such as the United States it is often practiced in conjunction with planning for pedestrians as a part of active transportation planning.

<span class="mw-page-title-main">Interchange (road)</span> Road junction that uses grade separation

In the field of road transport, an interchange or a grade-separated junction is a road junction that uses grade separations to allow for the movement of traffic between two or more roadways or highways, using a system of interconnecting roadways to permit traffic on at least one of the routes to pass through the junction without interruption from crossing traffic streams. It differs from a standard intersection, where roads cross at grade. Interchanges are almost always used when at least one road is a controlled-access highway or a limited-access divided highway (expressway), though they are sometimes used at junctions between surface streets.

<span class="mw-page-title-main">Controlled-access highway</span> Highway designed for high-speed, regulated traffic flow

A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway, and expressway. Other similar terms include throughway or thruway and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highways with somewhat less isolation from other traffic.

<span class="mw-page-title-main">2+1 road</span> Design of road

2+1 road is a specific category of three-lane road, consisting of two lanes in one direction and one lane in the other, alternating every few kilometres, and usually separated with a steel cable barrier. The second lane allows faster-moving traffic to overtake slower vehicles at regular intervals. Traditional roads of at least 10 metres (33 ft) width can be converted to 2+1 roads and reach near-motorway safety levels at a much lower cost than an actual conversion to motorway or dual carriageway.

<span class="mw-page-title-main">Structure gauge</span> Minimum clearance, height and width of railway infrastructure

A structure gauge, also called the minimum structure outline, is a diagram or physical structure that sets limits to the extent that bridges, tunnels and other infrastructure can encroach on rail vehicles. It specifies the height and width of station platforms, tunnels and bridges, and the width of the doors that allow access to a warehouse from a rail siding. Specifications may include the minimum distance from rail vehicles to railway platforms, buildings, lineside electrical equipment cabinets, signalling equipment, third rails or supports for overhead lines.

<span class="mw-page-title-main">Roadway departure</span> Type of single-vehicle collision

A roadway departure is a type of incident that occurs when a vehicle leaves the roadway. Such incidents can lead to a single-vehicle collision.

<span class="mw-page-title-main">Geometric design of roads</span> Geometry of road design

The geometric design of roads is the branch of highway engineering concerned with the positioning of the physical elements of the roadway according to standards and constraints. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Geometric design also affects an emerging fifth objective called "livability", which is defined as designing roads to foster broader community goals, including providing access to employment, schools, businesses and residences, accommodate a range of travel modes such as walking, bicycling, transit, and automobiles, and minimizing fuel use, emissions and environmental damage.

<span class="mw-page-title-main">Speed limits in the United States by jurisdiction</span>

Speed limits in the United States vary depending on jurisdiction. Rural freeway speed limits of 70 to 80 mph are common in the Western United States, while such highways are typically posted at 65 or 70 mph in the Eastern United States. States may also set separate speed limits for trucks and night travel along with minimum speed limits. The highest speed limit in the country is 85 mph (137 km/h), which is posted on a single stretch of tollway in exurban areas outside Austin, Texas. The lowest maximum speed limit in the country is 30 miles per hour (48 km/h) in American Samoa.

<span class="mw-page-title-main">Managed lane</span>

A managed lane is a type of highway lane that is operated with a management scheme, such as lane use restrictions or variable tolling, to optimize traffic flow, vehicle throughput, or both. Definitions and goals vary among transport agencies, but managed lanes are generally implemented to achieve an improved operational condition on a highway, such as improving traffic speed and throughput, reducing air pollution, and improving safety. Types of managed lanes include high-occupancy vehicle (HOV) lanes, high-occupancy toll lanes, express toll lanes, reversible lanes, and bus lanes. Most managed lane facilities are located in the United States and Canada, although HOV and bus lanes can be found in many other countries; outside of the US and Canada, many countries use active traffic management that manage all lanes of a highway.

In civil engineering, clearance refers to the difference between the loading gauge and the structure gauge in the case of railroad cars or trams, or the difference between the size of any vehicle and the width/height of doors, the width/height of an overpass or the diameter of a tunnel as well as the air draft under a bridge, the width of a lock or diameter of a tunnel in the case of watercraft. In addition, there is the difference between the deep draft and the stream bed or sea bed of a waterway.

References

  1. Theeuwes, Jan; Godthelp, Hans (June 1995). "Self-Explaining Roads". Safety Science . Vol. 19, no. 2–3. pp. 217–225. doi:10.1016/0925-7535(94)00022-U. ISSN   0925-7535.
  2. Theeuwes, Jan (March 4, 2021). "Self-Explaining Roads: What Does Visual Cognition Tell Us About Designing Safer Roads?". Cognitive Research: Principles and Implications. Vol. 6, no. 1. p. 15. doi: 10.1186/s41235-021-00281-6 . ISSN   2365-7464. PMC   8030273 . PMID   33661408.
  3. Wegman, Fred (January 1995). "Influence of Infrastructure Design on Road Safety". International Symposium on Traffic Safety: A Global Issue, Kuwait. No. D-95-1. Leidschendam, Netherlands: Institute for Road Safety Research (SWOV).
  4. 1 2 3 American Association of State Highway and Transportation Officials (2001). A Policy on Geometric Design of Highways and Streets (PDF) (4th ed.). Washington, DC: American Association of State Highway and Transportation Officials. pp. 507 (design speed), 510 (Exhibit 8–1: Maximum Grades for Rural and Urban Freeways). ISBN   1-56051-156-7. GDHS-4. Retrieved April 11, 2014.
  5. Port Huron Transportation Service Center. "I-94/I-69 Reconstruction in St. Clair County". Michigan Department of Transportation. Retrieved July 3, 2012.
  6. Pratcher, Shannon (February 12, 2021). "Why does I-35E through St. Paul have a 45-mph speed limit?". Star Tribune. Minneapolis. Retrieved August 12, 2024.
  7. "Interstate 670 Kansas / Missouri". AARoads: Interstate-Guide.com. July 1, 2022. Retrieved August 12, 2024.[ self-published source ]
  8. Rubin, Lawrence A. (1985). Bridging the Straits: The Story of Mighty Mac . Detroit: Wayne State University Press. ISBN   978-0-8143-1789-1.
  9. United States Congress. "Title 23, Chapter 1, Section §103". U.S. Government Printing Office. Retrieved May 31, 2012.