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Slaughter Alley is an American colloquial name given for sections of highway known for a high rates of fatal traffic accidents. Other terms include Blood Alley, Massacre Mountain, Deadliest Highway, Killer Highway (Canada), Route de la Mort (France), and El Camino de la Muerte (Bolivia). This last epithet is particularly attributed to the Yungas Road.
Many sections of roads have been known as "Slaughter Alley" and local residents may disagree on where "Slaughter Alley" actually is or was. Many famous "Slaughter Alleys" may no longer exist as they have been replaced by new, safer sections of road.
The United States began upgrading major highways to modern freeways in the 1950s. The freeways were much safer than the old highways because the opposing lanes were separated by barriers or wide medians and grade-level crossings were eliminated by overpasses and underpasses. The significantly lower rate of fatalities on the freeways caused the busy older highways to become notorious as areas with comparatively higher rates. Some older, narrow roads have not been widened to accommodate increased traffic over the years. In many regions, the most dangerous sections of these old highways became known locally as "Slaughter Alley" (or by other similar names). Over subsequent decades many of these roads were bypassed or upgraded to freeway status.
- Blood Alley or Death Trap Highway: California State Route 138 (Pearblossom Highway) east of Palmdale and west of Interstate 15.[dead link]
- Blood Alley: U.S. Highway 6 near Bolton, Connecticut, also known locally as "Suicide 6." Efforts to improve the road near this town have continually failed due to unresolvable conflicts of interest between local, state, and federal officials; the state officially abandoned freeway plans in 2003 in lieu of safety improvements on the existing road.
- Kamikaze Curve: New York Route 17 in Binghamton, New York, east of the junction with Interstates 81 and 88. The sharp curve along the base of a mountain is the site of dozens of fatal crashes since the highway's opening in the 1960s.
- Highway of Death: Connecticut Turnpike (I-95) between New Haven and the New York state line. The route is one of two main commuter routes between Connecticut and New York City, and part of the main truck route along the Eastern Seaboard. These two factors contribute to its high fatality rate. Long-term construction is underway to address congestion and the high accident rate on this stretch of highway.
- Blood Highway: California State Route 12 between Lodi, California and Rio Vista, California. This is a two-lane road that many big rig truckers use to go from State Route 160 to Interstate 5. There are many side roads with blind spots. This highway also allows passing in the opposite lane, which leads to increased head-on collisions and other accidents.Blood Highway” runs across over 140 miles of terrain, but the stretch from Lodi to Rio Vista is the main culprit behind State Route 12’s alter ego. Officials estimate more than 70 people have lost their lives traveling this segment of asphalt. An unusually high number of blind spots in conjunction with heavy traffic from truckers en route to Interstate 5 both contribute to the high number of fatalities.
- Death Alley: US Highway 1 The 18 mile stretch of US 1 in southern Miami-Dade County between Florida City, FL and the north end of Key Largo. The two lane road through South Glades, even with two passing zones added in the 1980's, still sees a disproportionate number of accidents. Historically, some of this have been attributed to a high number of intoxicated drivers in the northbound lane returning to Miami from day trips to the tiki bars of Key Largo and Islamorada and others pulling heavy loads such as boats or travel trailers at high speed.
Noted former "Slaughter Alleys"
- Slaughter Alley: U.S. Route 101 south of San Clemente, California (near the San Onofre Nuclear Generating Station). Bypassed by Interstate 5.
- Slaughter Alley: U.S. Route 101 in Cloverdale, California. Bypassed in the mid-1990s.
- Massacre Mountain: Old U.S. Highway 25E between Middlesboro, Kentucky and Cumberland Gap, Tennessee. Now a hiking and nature trail, replaced by the Cumberland Gap Tunnel.
- Blood Alley: U.S. Route 101 near San Jose, California. Last section upgraded to freeway status in 1984.
- Blood Alley: Route 21 in Jefferson County, Missouri, also referred to as "Missouri's Most Dangerous Highway". The majority has been rerouted to a new freeway, with the southern part near Hillsboro, Missouri currently under construction.
- Suicide Strip: US Route 58 between Emporia, Virginia and Suffolk, Virginia, earning the nickname when the then two-lane section was the scene of many multi-fatality accidents. Safety improved considerably with the completion of a parallel road to provide divided four-lane capacity in the early 1990s.
- Death Hill: The steep descent of Interstate 71/75 in Kenton County, Kentucky toward the Ohio River and Cincinnati. This stretch of road, now known as Cut-in-the-Hill, was reconstructed from 1989 to 1994, and the number of fatal accidents dropped dramatically. However, it still has a much higher accident rate than similar Kentucky highways.
- Highway to Heaven: The stretch of U.S. 27 in Butler County, Ohio running from Old Colerain in Cincinnati to Oxford, Ohio. Before it was widened and speed limits were lowered, it had a very high fatality rate.
- Bloody 66, Slaughter Lane: Stretches of the famous former U.S. Route 66, including the stretches from Glenrio, Texas to Tucumcari, New Mexico and in the vicinity of Oatman, Arizona. These have been bypassed by Interstate 40, yet still remain open. Fatalities decreased significantly because a large volume of traffic that had caused congestion on the largely two-lane highway was diverted to the four-lane limited-access interstate highway.
- Death Valley: A stretch of Interstate 40, Interstate 85, U.S. Route 421, U.S. Route 29, U.S. Route 70, and U.S. Route 220 that runs through Greensboro that was well known for a high number of accidents and fatalities. Since the completion of the southeastern half of the Greensboro Urban Loop in 2005, traffic and accidents have decreased significantly.
- Death Loop: A 20-mile section of FM 1604 (Loop 1604), that runs through the north side of San Antonio was well known for a high number of fatalities in the early 1980's (54 in 1 year). Once that section of the loop was converted from a two-lane Farm-to-Market Road into a two-lane median separated highway in the mid-80's, vehicular accidents and fatalities decreased tremendously.
- Suicide Alley: A stretch of U.S. Route 6 on Cape Cod in Massachusetts reduces to a two-lane freeway with plastic stanchions posted on a small asphalt median was known as "Suicide Alley" due to the high number of fatalities from head-on collisions before the median improvements were constructed. (When the two-lane freeway stretch was first built, it was marked with passing zones like any other two-lane highway. The small asphalt/stanchion median was built in stages beginning in 1989 and finishing in 1992.)
- Highway of Death: US-24 between Fort Wayne, Indiana and Toledo, Ohio. This was a two-lane route—the site of numerous fatal head-on collisions between cars and semi trucks—is bypassed with a freeway in northeast Indiana, and continuing into Ohio as a four-lane highway.
- El Camino de la Muerte (Road of Death): Yungas Road, a road 38 to 43 miles (61 to 69 km) long between La Paz and Coroico, in the Yungas region of Bolivia. A 20-year modernization project was finished in 2006, including enlargement to two lanes, asphalt pavement, new bridges, and by-pass to the north of the Chusquipata–Yolosa section. Considered by many to be the most dangerous road in the world.
- Eyre Highway on the Nullarbor Plain in southern Australia is said to be the straightest, flattest road in the world. In this case it is the monotony of the straight, narrow road combined with long trucks (road trains, the air blast from which can cause car drivers to lose control) that present the hazard.
- Highway 31 (Israel) in southern Israel, 24 km between Sdom and Arad said to be pinned with obelisks for the dead. Other parts of the road are prone to fatal accidents due to a single lane in each direction and lack of separation between the lanes. The 31 km of the road had been declared as red road (a road that has more than average number of fatal accidents) by Or Yarok
- Highway 11, between Lac du Bonnet and Traverse Bay in eastern Manitoba (50 kilometres (31 mi))
- Highway 103 in Nova Scotia which saw the death of 29 people between 2006 and 2009.
- Highway 1 A short, busy undivided section of the Trans-Canada highway through Headingley, Manitoba (6 kilometres (3.7 mi)).
- Between 2004 and 2009, the 400 kilometres (250 mi) undivided stretch of Highway 63 in Alberta saw 22 deaths and more than 250 injuries. The remote highway is the main route to Fort McMurray and has seen extraordinary increases in traffic volume with accelerated development of the Alberta Oil Sands. Between 2003 and 2015, a total of 190 people have died on Highway 63 and Highway 881. 
- A 14 kilometres (8.7 mi) section of Highway 1 through the Canadian Rockies. Funds were committed in 2008 to upgrade the highway.
- Highway 401 between London, Ontario and Windsor, Ontario was known as "Carnage Alley" due to a number of design factors: gravel shoulders that contributed to median-crossing collisions when a driver lost control of a vehicle, long, straight sections that promoted fatigue (often resulting in the driver drifting onto the gravel shoulder), and the potential of weather causing sudden severe driving conditions including whiteouts from sudden heavy snowfall and fog. Significant upgrades, including replacement of gravel with paved shoulders, improved signage, installation of tall-wall median barriers, and the widening of the 401 from four to six lanes between Windsor and Tilbury have been undertaken by the Ontario Ministry of Transportation (MTO) since a fatal pileup on Sept. 3, 1999.
- Ontario Highway 400 between Vaughan, Ontario and Barrie, Ontario.
- McCowan Road between 14th Avenue and Highway 7 in Markham, Ontario. The road is hazardous with heavy traffic and outdated narrow Rouge River bridge which experienced number of collisions.
The A3 motorway section from Nova Gradiška to Slavonski Brod is believed to be cursed, because of many accidents that happen there each year. In a year and a half, 12 people died and 21 were injured. Amongst others a well known Macedonian singer, Toše Proeski.
Roads called "Slaughter Alley" for reasons other than high fatal accident rates include:
- Florida State Road 29, because of a high number of Florida panthers killed there.
- The road from Kuwait to Basra (better-known as "Highway of Death") where the retreating Iraqi army was destroyed in the 1991 Gulf War by American forces.
- Featured in Dangerous World: Roads on the National Geographic Channel
- "Archived copy". Archived from the original on 2016-03-09. Retrieved 2016-02-17. channel 10 news,March 27 2015
- CAA, "The Top 12 Most Dangerous Highways in Canada", May 6th, 2009
- safer63and881, 
- CTV, "Feds fund project to twin 14 km of dangerous highway", August 5, 2008