{{Short description|Fuel economy improvement device}} '''Semi-trailer aerodynamic devices''' are devices affixed to semi-trailers, for the purpose of reducing aerodynamic drag caused by air turbulence. The two major types of device in use are '''trailer skirts''' (or '''side skirts'''), affixed to the underside of trailers, and '''trailer tails''' (or '''boat tails''', or '''rear fairings'''), affixed to the rear. Several such devices have been recognized by the U.S. Environmental Protection Agency's SmartWay Transport Partnership, making them eligible for funding under the Diesel Emissions Reduction Act.<ref name="epa">{{cite web | title = Verified Aerodynamic Technologies | work = SmartWay Technology: About the SmartWay Technology Program | publisher = Environmental Protection Agency | url = http://www.epa.gov/smartway/forpartners/technology.htm | archive-url = https://web.archive.org/web/20140122072858/http://epa.gov/smartway/forpartners/technology.htm | url-status = dead | archive-date = January 22, 2014 | access-date = September 17, 2014 }}</ref>
==Trailer skirts== {{Annotated image | image = Trailer skirt.jpg | image-width = 1000 | image-left = -90 | image-top = -420 | width = 240 | height = 130 | annotations = | caption = Detail of trailer skirt }} [[File:Trailer skirt.jpg|thumb|alt=Walmart truck with trailer skirts installed|A semi-trailer truck with trailer skirts installed]]
===Construction=== Trailer skirts comprise a pair of panels affixed to the lower side edges of a trailer, running most of the length of the trailer and filling the gap between the forward and rear axles. Trailer skirts are typically constructed of aluminum, plastic, or fiberglass, with plastic the most resistant to damage from side or bottom impacts.<ref name="trucknews">{{cite news | title = Trailer skirts: A proven fuel-saver | newspaper = trucknews.com | publisher = Business Information Group | url = http://www.trucknews.com/products/trailer-skirts-a-proven-fuel-saver | access-date = September 17, 2014 }}</ref> Skirts may have a modular design, allowing installation on a variety of trailer lengths.<ref name="truckinginfo">{{cite web | title = New Aerodynamic Trailer Skirt Technology Introduced | publisher = Trucking Info | date = March 26, 2013 | url = http://www.truckinginfo.com/channel/drivers/product/detail/2013/03/new-aerodynamic-trailer-skirt-technology-introduc.aspx | access-date = September 17, 2014 }}</ref> Skirts generally weigh between {{convert|70|and|160|kg|lb|abbr=on}}.<ref name="nrcan">{{cite web | title = Trailer side skirts | work = On the Road to a fuel-efficient truck: A Guide for Purchasing Aerodynamics for Heavy-Duty Tractors and Trailers | publisher = Natural Resources Canada | date = September 2009 | url = http://fleetsmart.nrcan.gc.ca/index.cfm?fuseaction=rfet.5 | access-date = September 17, 2014 }}</ref> Installation typically requires three to five {{dfn|person-hours|the amount of work performed by the average worker in one hour}}.<ref name="nrcan"/>
===Cost=== {{As of|2009}}, a set of trailer skirts cost between C$1500 and C$3000 (US$1300 to $2700).<ref name="nrcan"/> Standard trailer skirts have an estimated payback period of ten to eighteen months, while "advanced" skirts (those that improve fuel efficiency by over 7%) are estimated to pay for themselves in seven to fourteen months.<ref name="nrcan"/>
===Performance=== A 2012 investigation by SAE International of nine trailer skirt designs found that three provided fuel savings greater than 5%, and four provided savings between 4% and 5%, compared with an unmodified trailer.<ref name="sae">{{cite web | last = Wood | first = Richard | title = EPA Smartway Verification of Trailer Undercarriage Advanced Aerodynamic Drag Reduction Technology | publisher = SAE International | date = September 24, 2012 | url = http://papers.sae.org/2012-01-2043/ | access-date = September 17, 2014 }}</ref> Skirts with reduced ground clearance offer greater fuel savings; in one instance, reducing ground clearance from {{convert|16|in|cm|abbr=on}} to {{convert|8|in|cm|abbr=on}} resulted in an improvement in fuel savings from 4% to 7%.<ref name="trucknews"/> One 2008 Delft University of Technology study found fuel savings of up to 15% for the particular design studied.<ref name=delft>{{cite web | others = Delft University of Technology | title = Aerodynamic Truck Trailer Cuts Fuel And Emissions By Up To 15 Percent | publisher = Science Daily | date = April 22, 2008 | url = https://www.sciencedaily.com/releases/2008/04/080417105446.htm | access-date = September 17, 2014 }}</ref> Sean Graham, president of a major supplier of trailer skirts, estimates that in typical use, drivers see fuel savings of 5% to 6%.<ref name="trucknews"/>
Trailers with skirts fitted have also demonstrated reduced tire spray, and drivers have reported improved stability in crosswinds.<ref name="nrcan"/>
===Adoption=== As of 2018, over 60% of new trailers produced in Australia are equipped with skirts, whereas the figure is over 50% for the North American market.
A 2014 study by the North American Council for Freight Efficiency on adoption of fuel efficient technologies and practices found trailer skirts to be the most widely adopted technology of those studied, having been adopted by seven of the ten major shipping fleets in the study.<ref name="ccj">{{cite web | last = Dunn | first = Jill | title = Study: Fuel efficiency efforts pay off for carriers | work = Commercial Carrier Journal – Fleet Management Magazine | publisher = Randall-Reilly | date = September 8, 2014 | url = http://www.ccjdigital.com/study-fuel-efficiency-efforts-pay-off-for-carriers/ | access-date = September 17, 2014}}</ref>
Since the wide adoption of trailer skirts, incidents of them becoming detached and colliding with other vehicles have increased. On October 18, 2018, a trailer skirt came off of a tractor trailer traveling East in Knoxville, Tennessee and hit a westbound car, killing its driver.<ref>{{Cite web|url=https://www.wbir.com/article/news/local/kpd-names-driver-killed-by-flying-metal-piece-from-tractor-trailer/51-606500165|title=KPD names driver killed by flying metal piece from tractor-trailer|website=wbir.com}}</ref><ref>{{Cite web|url=https://www.trucks.com/2018/08/29/fleets-adopt-trailer-fuel-efficiency-tech/|title=Fleets Adopt Trailer Fuel-Efficiency Tech as Federal Rules Stall|date=August 29, 2018|website=Trucks.com}}</ref>
==Trailer tails== thumb|Trailer tail at the rear of a semi-trailer in 2013
Trailer tails, boat tails, or rear fairings comprise a set of panels, usually collapsible, which fold out from the rear of the trailer, creating a tapered shape that reduces drag from the low-pressure wake created behind the trailer. Trailer tails alone have demonstrated a fuel savings of 1%–5%, and in concert with trailer skirts, 9% improvement has been demonstrated.<ref name="epa2">{{cite web|title=SmartWay Verified List of Aerodynamic Devices|url=https://www.epa.gov/verified-diesel-tech/smartway-verified-list-aerodynamic-devices|publisher=U.S. Environmental Protection Agency|access-date=29 June 2016}}</ref>
TrailerTail is a registered trademark of STEMCO.<ref>{{cite web|url=http://www.stemco.com/product/trailertail/|title=TrailerTail® Fuel Savings Technology|access-date=2018-10-15|website=stemco.com}}</ref><ref>{{US trademark|77152970}}</ref>
===SuperTruck project=== At least one model of trailer tail, trade named TrailerTail, is part of Navistar's SuperTruck project,<ref>[http://www.truckersnews.com/supertruck-draws-navistar-attention/ Navistar SuperTruck] {{webarchive |url=https://web.archive.org/web/20110717104716/http://www.truckersnews.com/supertruck-draws-navistar-attention/ |date=July 17, 2011 }}</ref> which will use $37 million of US Department of Energy grants to build next generation trucks and tractor trailers.
==See also== *Teardrop trailer (truck), an aerodynamically shaped trailer in use in the UK
==References== {{reflist}}
Category:Vehicle parts Category:Automotive technologies Category:Shipping and the environment Category:Transportation engineering Category:Transport economics Category:Energy conservation