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98-409: A single-point urban interchange ( SPUI , / ˈ s p uː i / SPOO -ee or / ˈ s p juː i / SPEW -ee ), also called a single-point interchange ( SPI ) or single-point diamond interchange ( SPDI ), is a type of highway interchange . The design was created in order to help move large volumes of traffic through limited amounts of space efficiently. A SPUI is similar in form to

196-401: A diamond interchange but has the advantage of allowing opposing left turns to proceed simultaneously by compressing the two intersections of a diamond into one single intersection over or under the free-flowing road. The term "single-point" refers to the fact that all through traffic on the arterial street, as well as the traffic turning left onto or off the interchange, can be controlled from

294-735: A four-leaf clover . A cloverleaf is the minimum interchange required for a four-legged system interchange. Although they were commonplace until the 1970s, most highway departments and ministries have sought to rebuild them into more efficient and safer designs. The cloverleaf interchange was invented by Maryland engineer Arthur Hale, who filed a patent for its design on May   24, 1915. The first one in North America opened on December   15, 1929, in Woodbridge, New Jersey, connecting New Jersey Route   25 and Route   4 (now U.S. Route   1/9 and New Jersey Route   35). It

392-407: A teardrop shape, with the points facing towards the center of the interchange. Longer ramps are often required due to line-of-sight requirements at roundabouts. A partial cloverleaf interchange (often shortened to the portmanteau, parclo ) is an interchange with loops ramps in one to three quadrants, and diamond interchange ramps in any number of quadrants. The various configurations are generally

490-556: A yellow trap . When the signal turns yellow, a turning driver may assume oncoming traffic will stop and a crash may result. For this reason, the US bans sequences that may cause a yellow trap. This can also happen when emergency vehicles or railroads preempt normal signal operation. In the United States, signs reading "Oncoming traffic has extended green" or "Oncoming traffic may have extended green" must be posted at intersections where

588-950: A 'walk' light (normally a walking human figure, typically coloured green or white) and a 'don't walk' light (normally either a red or orange man figure or a hand), though other variations exist. Flashing red man: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely Red man: do not cross Red: do not cross Amber (steady, after green, before red): continue to cross only if unable to stop safely Flashing amber: cross with caution (often used in low-traffic crossing or after midnight) Flashing blue or green man: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely Red standing man: do not cross Amber: continue to cross only if unable to stop safely Flashing amber: cross with caution, obey signage (used when lights are out of order or shut down) Red: do not cross Red and amber: do not cross, prepare for green In Germany,

686-399: A SPUI takes up considerably less space than a full cloverleaf interchange , allowing construction to take place on a limited amount of property and minimizing state use of eminent domain . Finally, SPUIs are reportedly safer than other space-efficient interchange forms, such as (standard) diamond interchanges. Research suggests that, although there may not be a significant difference between

784-632: A case where the driver was speeding at 62 km/h in a street limited up to 40 km/h (55 % upper than the allowed speed). Criticism in South Korea says that this is unrealistic and unreasonable. In addition, this can cause multiple collisions due to sudden braking. In 2016 when speed limit was up to 60 km/h, proposed alternatives to this kind of collision were only roundabouts, speed compliance increase and speed practice reduction or elderly zones are also proposed solutions. Without an all-red phase, cross-turning traffic may be caught in

882-399: A complex appearance and are often colloquially described as Mixing Bowls , Mixmasters (for a Sunbeam Products brand of electric kitchen mixers ), or as Spaghetti Bowls or Spaghetti Junctions (being compared to boiled spaghetti ). However, they consume a significantly smaller area of land compared to a cloverleaf interchange. A combination interchange (sometimes referred to by

980-475: A directional T interchange) is typically used when a three-way interchange is required for two or three highways interchanging in semi-parallel/perpendicular directions, but it can also be used in right-angle case as well. Their connecting ramps can spur from either the right or left side of the highway, depending on the direction of travel and the angle. Directional T interchanges use flyover/underpass ramps for both connecting and mainline segments, and they require

1078-412: A dumbbell interchange or a dogbone interchange, is similar to the diamond interchange, but uses a pair of roundabouts in place of intersections to join the highway ramps with the crossroad. This typically increases the efficiency of the interchange when compared to a diamond, but is only ideal in light traffic conditions. In the dogbone variation, the roundabouts do not form a complete circle, instead having

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1176-508: A longer bridge of the free-flowing road to cross the wider area required for the SPUI intersection below. Because vehicles must be able to cross the pavement in six different ways, a SPUI generally has a very large area of uncontrolled pavement in the middle of the intersection. This can be unsafe particularly if drivers are unfamiliar with the interchange type. Drivers making a left turn may become confused as oncoming turning traffic passes them on

1274-667: A moderate amount of land and moderate costs since only two levels of roadway are typically used. Their name derives from their resemblance to the capital letter T, depending upon the angle from which the interchange is seen and the alignment of the roads that are interchanging. It is sometimes known as the "New England Y", as this design is often seen in the northeastern United States, particularly in Connecticut. This type of interchange features directional ramps (no loops, or weaving right to turn left) and can use multilane ramps in comparatively little space. Some designs have two ramps and

1372-407: A movement in the direction of the arrow. These are used because they are safer, cause less delay, and are more flexible. Flashing amber arrows will normally be located below the solid amber. Arrow aspects may be used to permit certain movements or convey other messages to road users. A green arrow may display to require drivers to turn in a particular direction only or to allow drivers to continue in

1470-454: A parclo AB features a loop ramp approaching the crossroad in one direction, and beyond the crossroad in the opposing direction, as in the example image. A diverging diamond interchange (DDI) or double crossover diamond interchange (DCD) is similar to a traditional diamond interchange, except the opposing lanes on the crossroad cross each other twice, once on each side of the highway. This allows all highway entrances and exits to avoid crossing

1568-530: A particular direction when the signal is red. Generally, a green phase is illuminated at the beginning of the green phase (a "leading turn") or at the end of the green phase (a "lagging turn"). An 'indicative arrow' may be displayed alongside a green light. This indicates to drivers that oncoming traffic is stopped, such that they do not need to give way to that traffic when turning across it. As right-turning traffic (left-side drive) or left-turning traffic (right-side drive) does not normally have priority, this arrow

1666-414: A particular direction, while the main lights for that approach are red, or that drivers can only travel in one particular direction. Alternatively, when combined with another green signal, they may indicate that turning traffic has priority over oncoming traffic (known as a "filter arrow"). Flashing amber arrows typically indicate that road users must give way (to other drivers and pedestrians) before making

1764-455: A pedestrian-controlled crosswalk. For this reason, Ontario is phasing out the use of flashing green signals and instead replacing them with arrows.) Popular in Vietnam and China, countdown lights are additional lights installed next to (or above or below) the main signal lights. The countdown light is displayed by a countdown number with different colors (usually red, yellow, green), matching

1862-462: A problem in cases where the arterial, or nonfreeway road, already requires a very wide bridge. The intersection of 97 Street , having seven throughlanes, with Yellowhead Trail in Edmonton , Alberta, Canada, though a diamond interchange in concept, required such a wide bridge that traffic-signal phasing allows this intersection to behave as a SPUI. A freeway-over SPUI (as in the lower photo) requires

1960-439: A safer modification of the cloverleaf design, due to a partial or complete reduction in weaving, but may require traffic lights on the lesser-travelled crossroad. Depending on the number of ramps used, they take up a moderate to large amount of land, and have varying capacity and efficiency. Parclo configurations are given names based on the location of and number of quadrants with ramps. The letter A denotes that, for traffic on

2058-412: A single set of traffic signals . Due to the space efficiency of SPUIs relative to the volume of traffic they can handle, the interchange design is used extensively in the reconstruction of existing freeways as well as constructing new freeways, particularly in dense urban environments. Sometimes a SPUI will allow traffic to proceed straight through from the offramp to the onramp; this usually happens when

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2156-543: A small angle and meet the non-freeway at almost right angles. These ramps at the non-freeway can be controlled through stop signs , traffic signals , or turn ramps. Diamond interchanges are much more economical in use of materials and land than other interchange designs, as the junction does not normally require more than one bridge to be constructed. However, their capacity is lower than other interchanges and when traffic volumes are high they can easily become congested. A double roundabout diamond interchange, also known as

2254-401: A three-level semi-directional T at Highway 407 and a two-level semi-directional T at Highway 401 . Service interchanges are used between a controlled-access route and a crossroad that is not controlled-access. A full cloverleaf may be used as a system or a service interchange. A diamond interchange is an interchange involving four ramps where they enter and leave the freeway at

2352-509: A three-way interchange. However, in a semi-directional T, some of the splits and merges are switched to avoid ramps to and from the passing lane , eliminating the major disadvantage of the directional T. Semi-directional T interchanges are generally safe and efficient, though they do require more land and are costlier than trumpet interchanges. Semi-directional T interchanges are built as two- or three-level junctions, with three-level interchanges typically used in urban or suburban areas where land

2450-442: A toll road meets another toll road or a free highway. They are also useful when most traffic on the terminating highway is going in the same direction. The turn that is used less often would contain the slower loop ramp. Trumpet interchanges are often used instead of directional or semi-directional T or Y interchanges because they require less bridge construction but still eliminate weaving. A full Y-interchange (also known as

2548-422: A traditional stack interchange. A three-level roundabout interchange features a grade-separated roundabout which handles traffic exchanging between highways. The ramps of the interchanging highways meet at a roundabout , or rotary, on a separated level above, below, or in the middle of the two highways. These interchanges can also be used to make a "linking road" to the destination for a service interchange, or

2646-411: A white background with a red line through it, emphasising that the turn is no longer allowed. These lights will also often have the words "no turn" displayed, or an explanatory reason why the turn is not allowed, such as "train" in the case of a rail or light rail crossing. A third type is known as a "doghouse" or "cluster head" – a vertical column with the two normal lights is on the right side of

2744-446: Is a 3-level stack, since the semi-directional ramps are spaced out far enough, so they do not need to cross each other at a single point as in a conventional 4-level stack. Stacks are significantly more expensive than other four-way interchanges are due to the design of the four levels; additionally, they may suffer from objections of local residents because of their height and high visual impact. Large stacks with multiple levels may have

2842-426: Is a subway or overpass. No provision of formal facilities means pedestrians will have to self-evaluate when it is safe to cross, which can be intimidating for pedestrians. With a "parallel walk" design, pedestrians walk alongside the traffic flow. A leading pedestrian interval may be provided, whereby pedestrians get a "walk" signal before the traffic gets a green light, allowing pedestrians to establish themselves on

2940-409: Is able to turn simultaneously without crossing the path of the opposing left turns. Because traffic passing through the interchange can be controlled by a single signal, vehicles can clear the intersection much more quickly than in a diamond interchange (which requires two sets of traffic signals). SPUIs also allow for wider turns, easing movement for large vehicles, such as trucks and RVs. Furthermore,

3038-437: Is also a variant of the inverted SPUI, which can be used when a side road ends at, rather than crossing, a free-flowing road. In this variant, one carriageway of the free-flowing road is grade-separated from the side road, as with a typical inverted SPUI, while the other carriageway of the free-flowing road is at-grade with but still separated from the side road, as found in a continuous green T- (or seagull) intersection . There

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3136-428: Is an alternative four-way directional interchange. The turbine interchange requires fewer levels (usually two or three) while retaining directional ramps throughout. It features right-exit, left-turning ramps that sweep around the center of the interchange in a clockwise spiral . A full turbine interchange features a minimum of 18 overpasses, and requires more land to construct than a four-level stack interchange; however,

3234-477: Is braided when at least one of the roadways reverses sides. It seeks to make left and right turns equally easy. In a pure braided interchange, each roadway has one right exit, one left exit, one right on-ramp, and one left on-ramp, and both roadways are flipped. The first pure braided interchange was built in Baltimore at Interstate 95 at Interstate 695 ; however, the interchange was reconfigured in 2008 to

3332-531: Is longer than 100 seconds, depending on the type of light, the following possibilities may occur: In South Korea, the yellow light dilemma zone is not legally recognized. In other words, when the yellow light is on, traffic may not pass the stop line or enter the intersection even if cannot safely stop when the light shows. This has been reaffirmed by the ruling of the Supreme Court of Korea in May 2024, for

3430-470: Is more expensive. In a three-level semi-directional T, the two semi-directional ramps from the terminating highway cross the surviving highway at or near a single point, which requires both an overpass and underpass. In a two-level semi-directional T, the two semi-directional ramps from the terminating highway cross each other at a different point than the surviving highway, necessitating longer ramps and often one ramp having two overpasses. Highway 412 has

3528-533: Is one such interchange in Pultney Township, Belmont County, Ohio , between State Route 7 (SR 7) and Interstate 470 (I-470) at 40°02′52″N 80°44′01″W  /  40.047657°N 80.733542°W  / 40.047657; -80.733542 . The ramps leading to and from I-470 run west of, but are not directly connected to, SR 7; these ramps form the "side road" at this interchange. The southbound carriageway of SR 7 bridges over

3626-553: Is similar to a standard SPUI but includes an additional grade separation allowing for free-flowing through traffic on the crossroad; such through traffic thus bypasses the signalized intersection. The remaining intersection, free of the crossroad's through traffic, uses a two-phase traffic signal for handling the left turns in pairs, similar to the traffic flow at an inverted SPUI. Examples include: Download coordinates as: Highway interchange Note: The descriptions of interchanges apply to countries where vehicles drive on

3724-405: Is used to allow turning traffic to clear before the next phase begins. Some variations exist on this set up. One version is a horizontal bar with five lights – the green and amber arrows are located between the standard green and amber lights. A vertical five-light bar holds the arrows underneath the standard green light (in this arrangement, the amber arrow is sometimes omitted, leaving only

3822-486: The 40th Street Bridge . The northbound carriageway of PA 28 passes under the interchange, with lefthand ramps meeting at the bridge (the northbound entrance ramp does not provide direct access to PA 28). The southbound carriageway of PA 28 has a continuous green T-intersection with the bridge. A similar interchange exists in Coal Grove, Ohio , at the junction of U.S. Route 52 (US 52) with

3920-629: The Ben Williamson Memorial Bridge and the Simeon Willis Memorial Bridge , which cross the Ohio River and lead to and from Ashland, Kentucky , respectively. The eastbound carriageway of US 52 passes under the interchange, with lefthand exit and entrance ramps to the bridges. The westbound carriageway of US 52, which narrows to one throughlane, has a continuous green T-intersection with

4018-400: The controlled-access highway , the loop ramps are located in advance of (or approaching ) the crossroad, and thus provide an onramp to the highway. The letter B indicated that the loop ramps are beyond the crossroad, and thus provide an offramp from the highway. These letters can be used together when opposite directions of travel on the controlled-access highway are not symmetrical, thus

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4116-498: The righthand side. Due to the large intersection area, the traffic lights need a longer yellow and red phase to clear the intersection, and, even then, it may not be long enough for a bicyclist entering on green or yellow to make it across before opposing traffic gets a green. In general, SPUI designs should not be used where bicycle traffic is expected unless fairly substantial changes to the design or special accommodations are provided. Pedestrians are usually not able to get through

4214-806: The "granddaddy of the urban interchange". This design has since been altered to include frontage roads in each direction. Several SPUIs, built in the 1970s and later, are located on German autobahns, like the A40 , A42 , A44 , A46 , A57 , A59 , and A113 in Berlin . There is also a SPUI on the Frankenschnellweg , the urban part of the A73 , and Maximilianstraße, in Nuremberg (at 49°27′06″N 11°02′17″E  /  49.451708°N 11.038102°E  / 49.451708; 11.038102 ). Smaller versions of

4312-403: The "inside" through road (on the same side as the freeway that ends) crossing each other at a three-level bridge. The directional T interchange is preferred to a trumpet interchange because a trumpet requires a loop ramp by which speeds can be reduced, but flyover ramps can handle much faster speeds. The disadvantage of the directional T is that traffic from the terminating road enters and leaves on

4410-599: The "yellow trap" condition exists. The United States is not party to the Vienna Convention ; rather, the Manual on Uniform Traffic Control Devices (MUTCD) outlines correct operation in that country. In the US, a single signal head may have three, four, or five aspects (though a single aspect green arrow may be displayed to indicate a continuous movement). The signals must be arranged red, amber, and green vertically (top to bottom) or horizontally (left to right). In

4508-430: The 'Walk' symbol will illuminate for pedestrians. At the end of the crossing phase, the 'Don't Walk' symbol will flash, as will the amber traffic light. Pedestrians are usually incorporated into urban signalised junctions in one of four ways: no facilities, parallel walk, walk with traffic, or all-red stages. No facilities may be provided if pedestrian demand is low, in areas where pedestrians are not permitted, or if there

4606-504: The 1950s. One of the best historical examples of computerized control of lights was in Denver in 1952. In 1967, the city of Toronto was the first to use more advanced computers that were better at vehicle detection. The computers maintained control over 159 signals in the cities through telephone lines. A set of lights, known as a signal head, may have one, two, three, or more aspects. The most common signal type has three aspects facing

4704-495: The Maritime provinces, lights are often arranged horizontally, but each aspect is a different shape: red is a square (larger than the normal circle) and usually in pairs at either end of the fixture, amber is a diamond, and green is a circle. In many southern and southwestern U.S. states, most traffic signals are similarly horizontal in order to ease wind resistance during storms and hurricanes. Japanese traffic signals mostly follow

4802-618: The SPUI can also be found on non-autobahn roads in German cities, with right-turning traffic under signal control, located in Heilbronn , Karlsruhe , Sindelfingen , Stuttgart , and Wiesbaden . SPUIs are also found in Australia, Canada, Hong Kong, Indonesia, and Singapore. A rarely built variant of the SPUI is the inverted SPUI , in which the carriageways of the free-flowing road are separated, with left on- and offramps running between

4900-483: The UK, normal traffic lights follow this sequence: A speed sign is a special traffic light, variable traffic sign , or variable-message sign giving drivers a recommended speed to approach the next traffic light in its green phase and avoid a stop due to reaching the intersection when lights are red. Pedestrian signals are used to inform pedestrians when to cross a road. Most pedestrian signal heads will have two lights:

4998-432: The UK, this type of crossing is called a pelican crossing , though more modern iterations are puffin and pedex crossings. In the UK, these crossings normally need at least four traffic signals, which are of a regular type (red, amber, and green), two facing in each direction. Furthermore, pedestrians will be provided with push buttons and pedestrian signals, consisting of a red and green man. Farside signals are located across

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5096-492: The US, a single-aspect flashing amber signal can be used to raise attention to a warning sign and a single-aspect flashing red signal can be used to raise attention to a "stop", "do not enter", or "wrong way" sign. Flashing red or amber lights, known as intersection control beacons , are used to reinforce stop signs at intersections. The MUTCD specifies the following vehicular signals: In the Canadian province of Quebec and

5194-485: The United States opened on July   7, 2009, in Springfield, Missouri , at the junction of Interstate 44 and Missouri Route 13 . A single-point urban interchange (SPUI) or single-point diamond interchange (SPDI) is a modification of a diamond interchange in which all four ramps to and from a controlled-access highway converge at a single, three-phase traffic light in the middle of an overpass or underpass. While

5292-401: The bridges are generally short in length. Coupled with reduced maintenance costs, a turbine interchange is a less costly alternative to a stack. A windmill interchange is similar to a turbine interchange, but it has much sharper turns, reducing its size and capacity. The interchange is named for its similar overhead appearance to the blades of a windmill . A variation of the windmill, called

5390-523: The bridges. The ramps cross each other at-grade , with a traffic light -controlled intersection. An interchange, like that in Millvale, Pennsylvania, formerly existed at the junction of SR 7 and SR 822 at the now-demolished Fort Steuben Bridge in Steubenville, Ohio . The northbound carriageway of SR 7 passed under the bridge, with lefthand ramps meeting the bridge approach, while

5488-410: The carriageways and coming to a single at-grade intersection with the cross street. This can be built less expensively than a standard SPUI by allowing for shorter, simpler bridges at the interchange. However, this inverts the usual convention of placing carriageway on- and offramps on the right side of the carriageway, instead placing them on the left side, usually considered the passing lane . There

5586-413: The color of the light on. When the light counts to "0" (or 1), the main light color immediately changes. Countdown lights may have zeros in the tens or none, some countdown lights may flash when getting ready to zero. Yellow lights can also have countdown lights, but most lights do not. Usually the countdown light has 2 digits, in case the time of the main light (usually the red light, rarely the green light)

5684-507: The compact design is safer, more efficient, and offers increased capacity—with three light phases as opposed to four in a traditional diamond, and two left turn queues on the arterial road instead of four—the significantly wider overpass or underpass structure makes them more costly than most service interchanges. Since single-point urban interchanges can exist in rural areas, such as the interchange of U.S. Route 23 with M-59 in Michigan ;

5782-537: The creation of a new basic road as a service interchange. Trumpet interchanges may be used where one highway terminates at another highway, and are named as such for to their resemblance to trumpets . They are sometimes called jug handles . These interchanges are very common on toll roads , as they concentrate all entering and exiting traffic into a single stretch of roadway, where toll plazas can be installed once to handle all traffic, especially on ticket-based tollways . A double-trumpet interchange can be found where

5880-454: The crossing before vehicles begin to turn, to encourage drivers to give way. A 'walk with traffic' facility allows pedestrians to go at the same time as other traffic movements with no conflict between movements. This can work well on one-way roads, where turning movements are banned or where the straight-ahead movement runs in a different stage from the turning movement. A splitter island could also be provided. Traffic will pass on either side of

5978-406: The crossing, while nearside signals are located below the traffic lights, facing in the direction of oncoming traffic. A HAWK beacon is a special type of traffic used in the US at mid-block crossings. These consist of two red signals above a single amber signal. The beacon is unlit until a pedestrian pushes the cross button. Then an amber light will show, followed by both red lights, at which point

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6076-448: The diverging windmill, increases capacity by altering the direction of traffic flow of the interchanging highways, making the connecting ramps much more direct. There also is a hybrid interchange somewhat like the diverging windmill in which left turn exits merge on the left, but it differs in that the left turn exits use left directional ramps. A braided or diverging interchange is a two-level, four-way interchange. An interchange

6174-518: The fine for crossing a red light if caught is as of 2019 between €5 and €10. Flashing green man or no man: do not start to cross (only at mid-block crossings); if it appears during crossing, then continue to cross if unable to stop safely Red standing man: do not cross WALK DONT WALK Modern version: White walking man: cross with caution Flashing orange stophand: do not start to cross; if it appears during crossing, then continue to cross if unable to stop safely Orange stophand: do not enter

6272-473: The first roads to feature grade-separations. Maryland engineer Arthur Hale filed a patent for the design of a cloverleaf interchange on May   24, 1915, though the conceptual roadwork was not realised until a cloverleaf opened on December   15, 1929, in Woodbridge, New Jersey , connecting New Jersey Route 25 and Route 4 (now U.S. Route 1/9 and New Jersey Route 35 ). It

6370-702: The flow of traffic. Traffic lights normally consist of three signals, transmitting meaningful information to road users through colours and symbols, including arrows and bicycles. The regular traffic light colours are red to stop traffic, amber for traffic change, and green for allowing the traffic, arranged vertically or horizontally in that order. Although this is internationally standardised, variations in traffic light sequences and laws exist on national and local scales. Traffic lights were first introduced in December 1868 on Parliament Square in London to reduce

6468-399: The green arrow below the steady green light, or possibly an LED -based device capable of showing both green and amber arrows within a single lamp housing). Some newer LED turn arrows seen in parts of Canada are capable of multicoloured animation. Such lights will often display a flashing and animated green or amber arrow when the dedicated turn is allowed but then transform into a red arrow on

6566-549: The interchange, while its northbound carriageway remains at-grade. SR 7's left on- and offramps run between its carriageways, meeting the I-470 ramps at an at-grade intersection. The I-470 ramps proceed to a trumpet interchange with I-470. I-470 itself bridges over both carriageways of SR 7 a short distance north of the I-470/SR ;7 ramps' intersection. This design was likely chosen not for cost savings but because

6664-518: The intersection Green walking man: safe to cross Red Man: Do Not Cross. If it appears during crossing, then continue to cross if unable to stop safely. Green Man: Safe to Cross. Where pedestrians need to cross the road between junctions, a signal-controlled crossing may be provided as an alternative to a zebra crossing or uncontrolled crossing. Traffic lights are normally used at crossings where vehicle speeds are high, where either vehicle or pedestrian flows are high or near signalised junctions. In

6762-414: The intersection with one green light. It can take up to four cycles to walk through the entire length of a SPUI. Finally, SPUIs can be somewhat difficult to clear of snow. The large area in which lanes cross may have to be shut down to allow efficient and thorough cleaning lest a snowplow leave piles of snow, interfering with traffic and visibility in the middle of the uncontrolled pavement. Additionally, if

6860-431: The island and pedestrians can cross the road safely between the other flows. An all-red stage, also known as a full pedestrian stage, a pedestrian scramble or a Barnes Dance, holds all vehicular traffic at the junction to allow pedestrians time to safely cross without conflict from vehicles. It allows allows the use of diagonal crossings. This may require a longer cycle time and increase pedestrian wait periods, though

6958-417: The need for police officers to control traffic. Since then, electricity and computerised control have advanced traffic light technology and increased intersection capacity. The system is also used for other purposes, including the control of pedestrian movements, variable lane control (such as tidal flow systems or smart motorways ), and railway level crossings . The first system of traffic signals, which

7056-404: The normal green lamp flashes rapidly, indicating permission to go straight as well as make a left turn in front of opposing traffic, which is being held by a steady red lamp. (This "advance green", or flashing green can be somewhat startling and confusing to drivers not familiar with this system. This also can cause confusion amongst visitors to British Columbia, where a flashing green signal denotes

7154-455: The northbound carriageway of SR 7 is bordered by railroad tracks, commercial properties, and the Ohio River and because I-470 bridges the river just east of SR 7—a more conventional interchange design was likely more difficult to achieve. There is another such interchange in Millvale, Pennsylvania , near Pittsburgh , at the junction between Pennsylvania Route 28 (PA 28) and

7252-512: The oncoming traffic: red on top, amber (yellow) below, and green below that. Additional aspects may be fitted to the signal, usually to indicate specific restrictions or filter movements. The 1968 Vienna Convention on Road Signs and Signals Chapter III provides international standards for the setup of traffic signal operations. Not all states have ratified the convention. A three-colour signal head should have three non-flashing lights which are red, amber , and green, either arranged horizontally (on

7350-806: The one in London were in use all over the United States . These traffic signals were controlled by a traffic officer who would change the commands on the signal to direct traffic. In 1912, the first electric traffic light was developed by Lester Wire , a policeman in Salt Lake City , Utah . It was installed by the American Traffic Signal Company on the corner of East 105th Street and Euclid Avenue in Cleveland , Ohio. The first four-way, three-colour traffic light

7448-594: The opposite direction of travel and saves one signal phase of traffic lights each. The first DDIs were constructed in the French communities of Versailles ( A13 at D182), Le Perreux-sur-Marne ( A4 at N486) and Seclin ( A1 at D549), in the 1970s. Despite the fact that such interchanges already existed, the idea for the DDI was "reinvented" around 2000, inspired by the freeway-to-freeway interchange between Interstate 95 and I-695 north of Baltimore . The first DDI in

7546-513: The passing lane, so the semi-directional T interchange (see below) is preferred. The interchange of Highway 416 and Highway 417 in Ontario, constructed in the early 1990s, is one of the few directional T interchanges, as most transportation departments had switched to the semi-directional T design. As with a directional T interchange, a semi-directional T interchange uses flyover (overpass) or underpass ramps in all directions at

7644-543: The portmanteau, cloverstack ) is a hybrid of other interchange designs. It uses loop ramps to serve slower or less-occupied traffic flow , and flyover ramps to serve faster and heavier traffic flows. If local and express ways serving the same directions and each roadway is connected righthand to the interchange, extra ramps are installed. The combination interchange design is commonly used to upgrade cloverleaf interchanges to increase their capacity and eliminate weaving. Some turbine-stack hybrids: The turbine interchange

7742-467: The problem of weaving, and due to the semi-directional flyover ramps and directional ramps, they are generally safe and efficient at handling high traffic volumes in all directions. A standard stack interchange includes roads on four levels, also known as a 4-level stack, including the two perpendicular highways, and one more additional level for each pair of left-turn ramps. These ramps can be stacked (cross) in various configurations above, below, or between

7840-419: The ramps connect with frontage roads . Since most through traffic travels over or under the intersection, the SPUI is still much more efficient than a surface intersection. The most commonly cited advantages of SPUIs are improved operation efficiency and safety as well as reduced right-of-way requirements compared to other interchange forms. Left-turning traffic from both directions of the intersecting roadways

7938-587: The right side of the road. For left-side driving, the layout of junctions is mirrored. Both North American (NA) and British (UK) terminology is included. The concept of the controlled-access highway developed in the 1920s and 1930s in Italy, Germany, the United States, and Canada. Initially, these roads featured at-grade intersections along their length. Interchanges were developed to provide access between these new highways and heavily-travelled surface streets. The Bronx River Parkway and Long Island Motor Parkway were

8036-455: The rightmost lane. After demerging from right-turning traffic, they complete their left turn by crossing both highways on a flyover ramp or underpass. The penultimate step is a merge with the right-turn on-ramp traffic from the opposite quadrant of the interchange. Finally, an on-ramp merges both streams of incoming traffic into the left-bound highway. As there is only one off-ramp and one on-ramp (in that respective order), stacks do not suffer from

8134-421: The road is extended. US 70 and US 17 west of New Bern, North Carolina is an example. A stack interchange is a four-way interchange whereby a semi-directional left turn and a directional right turn are both available. Usually, access to both turns is provided simultaneously by a single off-ramp. Assuming right-handed driving, to cross over incoming traffic and go left, vehicles first exit onto an off-ramp from

8232-458: The same rule except that the green "go" signals are referred to as 青 (ao), typically translated as "blue", reflecting a historical change in the Japanese language . As a result, Japanese officials decreed in 1973 that the "go" light should be changed to the bluest possible shade of green, bringing the name more in line with the color without violating the international "green means go" rule. In

8330-502: The side opposite to the direction of traffic) or vertically (with red on top). A two-colour signal head may be used in temporary operation and consists of red and green non-flashing lights. In both cases, all lights should be circular or arrow-shaped. Permissible signals for regulating vehicle traffic (other than public transport vehicles) are outlined in Article 23: Green arrows are added to signals to indicate that drivers can travel in

8428-482: The signal, a vertical column with the two arrows is located on the left, and the normal red signal is in the middle above the two columns. Cluster signals in Australia and New Zealand use six signals, the sixth being a red arrow that can operate separately from the standard red light. In a fourth type, sometimes seen at intersections in Ontario and Quebec , Canada, there is no dedicated left-turn lamp per se. Instead,

8526-733: The southbound carriageway had a continuous green T-intersection with the bridge. An offset SPUI is similar to a diamond interchange, however, by making two of the ramps flyovers or flyunders , all ramps are pushed to one side of the highway, where they meet the surface street at a single intersection. An example of this is the interchange between Interstate 225 and Alameda Avenue near the Town Center at Aurora shopping center in Aurora, Colorado , United States (at 39°42′40″N 104°49′33″W  /  39.711189°N 104.825807°W  / 39.711189; -104.825807 ). A three-level SPUI

8624-838: The term single-point diamond interchange is considered the correct phrasing. Single-point interchanges were first built in the early 1970s along U.S. Route 19 in the Tampa Bay area of Florida , including the SR 694 interchange in St. Petersburg and SR 60 in Clearwater . Traffic light#Rules Traffic lights , traffic signals , or stoplights – also known as robots in South Africa , Zambia , and Namibia – are signaling devices positioned at road intersections , pedestrian crossings , and other locations in order to control

8722-502: The two interchanging highways. This makes them distinct from turbine interchanges, where pairs of left-turn ramps are separated but at the same level. There are some stacks that could be considered 5-level; however, these remain four-way interchanges, since the fifth level actually consists of dedicated ramps for HOV /bus lanes or frontage roads running through the interchange. The stack interchange between I-10 and I-405 in Los Angeles

8820-470: The two types of interchanges in terms of total collisions, the injury and fatality rates are notably lower for SPUIs than diamond interchanges. The major disadvantage of SPUIs over other types of road junctions is the increased cost due to the need for a longer or wider bridge. A freeway-under SPUI (as in the upper diagram) requires a wider bridge over the free-flowing road to make room for the compressed on- and offramps. However, this disadvantage poses less of

8918-478: The use of the timer was that it saved cities money by replacing traffic officers. The city of New York was able to reassign all but 500 of its 6,000 officers working on the traffic squad, saving the city $ 12,500,000. In 1923, Garrett Morgan patented a design of a manually operated three-way traffic light with moving arms. The control of traffic lights made a big turn with the rise of computers in America in

9016-429: The wide area of uncontrolled pavement is on a bridge, as in the diagram, the snow cannot be pushed to the sides of the bridge as it may pose a hazard to the road underneath. This problem can be exacerbated by the comparatively large bridge width required by the SPUI. Given that a SPUI allows only left and right turns, drivers may not reenter the freeway they are departing (if, for example, they realize that they have taken

9114-541: The wrong exit) within a SPUI. Three-phase traffic signals are required. Other interchange types designed for efficiency, such as the six-ramp partial cloverleaf and the diverging diamond , require just two signal phases. The first SPUI opened on February 25, 1974, along U.S. Route 19 ( State Road 55 ), which goes over State Road 60 east of Clearwater, Florida . It was designed by Wallace Hawkes, Director of Transportation Engineering at J. E. Greiner Company (later URS Corporation ), who has been called

9212-478: Was a semaphore traffic signal, was installed as a way to replace police officer control of vehicular traffic outside the Houses of Parliament in London on 9 December 1868. This system exploded on 2 January 1869 and was thus taken down. But this early traffic signal led to other parts of the world implementing similar traffic signal systems. In the first two decades of the 20th century, semaphore traffic signals like

9310-540: Was considered a revolutionary design at the time of its construction. A cloverleaf offers uninterrupted connections between two roads but suffers from weaving issues. Along the mainline, a loop ramp introduces traffic prior to a second loop ramp providing access to the crossroad, between which ingress and egress traffic mixes. For this reason, the cloverleaf interchange has fallen out of favour in place of combination interchanges . Some may be half cloverleaf containing ghost ramps which can be upgraded to full cloverleafs if

9408-566: Was created by William Potts in Detroit, Michigan in 1920. His design was the first to include an amber 'caution' light along with red and green lights. Potts was Superintendent of Signals for the Police Department of Detroit. He installed automatic four-way, three-colour traffic lights in 15 towers across Detroit in 1921. By 1922, traffic towers were beginning to be controlled by automatic timers more widely. The main advantage of

9506-436: Was designed by Philadelphia engineering firm Rudolph and Delano, based on a design seen in an Argentinian magazine. A system interchange connects multiple controlled-access highways, involving no at-grade signalised intersections. A cloverleaf interchange is a four-legged junction where left turns across opposing traffic are handled by non-directional loop ramps. It is named for its appearance from above, which resembles

9604-596: Was designed by Philadelphia engineering firm Rudolph and Delano based on a design seen in an Argentinian magazine. The first cloverleaf in Canada opened in 1938 at the junction of Highway 10 and what would become the Queen Elizabeth Way . The first cloverleaf outside of North America opened in Stockholm on October   15, 1935. Nicknamed Slussen , it was referred to as a "traffic carousel" and

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