Cataloged here are many of the terms and phrases used throughout AARoads and in highway discussion overall. The nomenclature varies among the different departments of transportation charged with maintaining roads and highways across the United States. While certainly not a comprehensive list, modernization of roads and the implementation of electronic toll technology continues to evolve terminology commonly used by news sites, social media and road enthusiasts alike. Feel free to connect with us via email or social media if we omitted something or should expand this list further.
Invented in Mexico by civil engineer Francisco Mier, the continuous flow intersection or CFI was developed as a lower cost transportation solution for congested intersections. The design both costs less than conventional interchanges or SPUI’s and requires less right of way. The CFI reduces construction time and requires minimal closures to existing facilities to build.
The CFI separates traffic turning left from a highway mainline at a crossover signal a few hundred feet ahead of the main intersection. While oncoming traffic is stopped, motorists turning left cross the oncoming lanes and enter a far left turn lane at the main intersection. Since drivers have already crossed the lanes of oncoming traffic, they will turn left onto the cross street at the same time that through traffic is also moving. This configuration eliminates the extra step in the light cycle required to move left turns through separately and allows extra “green light time” to be redistributed throughout the intersection.
Initial CFI’s were implemented by 2005 in Baton Rouge, Louisiana, Maryland and New York with positive results.
A routed highway that is maintained at the county level. These roads are mostly signed on a pentagon shield with yellow text on blue background. Variations exist such as where Wisconsin uses lettered rectangles for county trunk highways, West Virginia with circle shields for their county routes and Missouri's lettered routes posted on square markers.<br>
County routes originated in 1958 with the formation of the California County Route Marker Program. Signs were designed to display the county and route number in a blue and gold color scheme for California. Routes were established to mark routes of major importance that were of general public interest, built to sufficient standards and with a logical beginning and end point. The success of the program in California led its adoption as the National Uniform County Route Marker Program by the National Association of Counties (NACO) in 1967. The blue and gold sign style remained the same and continues through today. More on the origins of the County Road pentagon and the source for our description is found here.
Interchanges in all states are numbered to reduce motorist confusion and to enable motorists to determine distances between exits within a state. Normally, one of two exit numbering methodologies is used: mileage-based or sequential. Mileage-based exit numbering systems have exit numbers that correspond to the nearest milepost, with the zero milepost normally at the southern or western end of the route. Sequential exit numbering simply starts with exit one and counts upward in a northerly or easterly direction. The mileage-based numbering system is preferred since it both allows motorists to easily reference the distance between two exits by calculating the difference between the two exits while also not upsetting the preexisting interchange numbers when a new interchange is constructed. If more than one exit is within the same milepost zone, then the exits are identified by letter suffixes (A, B, C, etc.), with the lowest letter (A) being applied to the exit that is the furthest to the west or south. Some states used to implement geographical lettering patterns, such as E/W or N/S to identify specific exits, but that convention is mostly phased out with some exceptions in the Northeast. FHWA mandates that all states use mileage based exit numbers by 2020, so eventually sequential based systems will be of historical nature only.
Express lanes were originally used for dual freeway segments where the inside carriageways provided limited ingress and egress points, allowing for higher speeds and better traffic flow due to the lack of merging traffic. A six mile segment of Interstate 96 from Livonia to Detroit, Michigan and Interstate 80 through Patterson, New Jersey include examples of this type of express lanes. Express lanes nowadays referred to toll lanes or tolled carriageways incorporated into a toll free freeway. Interstate 595 (Port Everglades Expressway) in Broward County and Interstate 95 east of Baltimore incorporate Express Lanes where motorists may use the high speed lanes for a variable toll rate. Express Lanes differ from High Occupancy Toll (HO/T) lanes in that all motorists are levied a fee regardless of the number of passengers present.
Projects in 2016 and beyond add Express Lanes to overall toll roads, allowing commuters on the Homestead Extension of Florida's Turnpike, the Beachline Expressway (SR 528) at Orlando and Veterans Expressway (SR 589) at Tampa, Florida to pay a higher rate to bypass the toll road mainlines.
In 1964, the state of California decided to eliminate or curtail most of the U.S. routes within its borders. This action was intended to reduce route-numbering confusion for U.S. routes parallel to new Interstate highway corridors, but it also resulted in the creation of several lengthy state routes that replaced the original U.S. routes. Some of the routes eliminated in 1964 were U.S. 40, 60, 66, 70, 80, 91, 99, 101A, 399 and 466. Other routes, such as U.S. 50, 101 and 395 were curtailed in length. Remnants of these routes include today's California 60 (U.S. 60), California 86 (old U.S. 99), California 91 (U.S. 91), California 99 (old U.S. 99), Interstate 10 (old U.S. 60-70) and Interstate 40 (old U.S. 66).
A Michigan Left is a type of intersection where motorists make a series of right or U-turns instead of a normal left-hand turn. The design eliminates left turns at congested intersections to help speed along through-traffic. They are named after Michigan, because it was the first state to implement them.
The Utah Department of Transportation (UDOT) refers to their version as a “ThrU Turn Intersection,” or TTI for short.
Some interchanges utilize features of both a diamond and a cloverleaf interchange. These interchanges may feature one or more loop ramps in addition to diamond ramps. They might be used in cases where real estate for the interchange is limited or when there is significantly higher traffic volume in one direction over another. Types include the parclo A2, where the loop ramps form on-ramps, parclo B2 where the loop ramps are off-ramps, and parclo B4, which utilizes six ramps with multiple on-ramps but a single off-ramp. See Kurumi’s Diamond/Cloverleaf Interchanges for more.
A traffic signal backplate surrounds a light to help it stand out against the sky or background. An option in the MUTCD allows departments of transportation to add a yellow retroreflective borders. A 1998 study conducted by the Insurance Corp. of British Columbia and the Canadian National Committee on Uniform Traffic Control, investigated the effectiveness of applying retroreflective tape around the borders of traffic signal backplates. The investigation concluded that the enhancement was effective at reducing crashes.
Following the Canadian study, yellow backplates were installed at three intersections in Columbia, South Carolina. An intersection safety case study revealed that the three locations experienced a 28.6 percent reduction in total crashes during a 25 month period.
An added benefit is that the retroreflective borders add visibility to signal heads during power outages. This draws extra attention for motorists to treat the dark signals as a four-way stop.
Source: “Traffic signals on Clairemont Avenue get shiny new look.” Leader-Telegram (Eau Claire, WI), December 28, 2013.
All four route classes utilize letter suffixes in some form across the United States. Cases for suffixed routes include the scenario where a highway divides into two alternative routes and neither route is considered to be the “main” route. U.S. 49E (east) and 49W (west) in Mississippi, where the east branch serves Greenwood and the west branch serves Indianola, is an example of this.
Another instance occurs along state and county roads when a route separates into multiple segments. Mississippi 9W provides a west branch of SR 9 to Oxford for instance, while three respective branches of Santa Rosa County 191 in Florida are signed as 191A, 191B and 191C.
Most suffixed routes in the Interstate Highway System were eliminated due to motorist confusion as advocated by AASHTO starting in 1973. Exceptions until 2012 included the two partitions of Interstate 35 at Minneapolis/St. Paul and Dallas/Fort Worth. The Congressionally designated IH 69 corridor in South Texas designated three new suffixed routes.
A traffic light is a device used to control movements at an intersection or at-grade crossing between two roads. Standard signals use three lens orientated from top to bottom or left to right with red, amber and green. Signals vary in housing styles based upon manufacturer and color schemes from state to state, and in municipalities throughout the country.
Variations of signals include the five-lens doghouse signal with left or right turn arrows, the four or five signal stacked signals, with amber and yellow turn arrows at the bottom, and upside down T signals with a green arrow positioned along side a green ball lens.
Backplates are added to signals to add visibility against the sky or background. Visors vary between full tunnel or cutout assemblies.
Unsigned routes can be one of two things: first, a highway may be primarily signed with one designation (such as a U.S. highway) but also carry another designation (such as a state route). These hidden designations include U.S. routes that silently merge onto an Interstate highway and hidden state route control numbers used by various departments of transportation throughout the country. An example is U.S. 87, which is the unsigned counterpart running alongside Interstate 25 in Colorado.
A second definition of an unsigned route is a route that may be maintained by the state and has a state route number but is not signed in the field. An example is the stretch of California 1 near Emma Wood State Beach, which is an unmarked state route.