Editing Curb extension (section)

==Design, advantages and disadvantages==
The Pedestrian and Bicycle Information Center, a body funded by the US Federal Highway Administration,<ref>{{cite web |title=About |url=https://www.pedbikeinfo.org/about.cfm |website=PedBikeInfo |access-date=27 June 2023}}</ref> advises that curb extensions ought not encroach on travel lanes, bicycle lanes, or shoulders, and should not extend more than 1.8&nbsp;m (6&nbsp;ft) from the curb.<ref>Pedestrian and Bicycle Information Center, "Crossing Enhancements,"  http://www.walkinginfo.org/engineering/crossings-enhancements.cfm {{Webarchive|url=https://web.archive.org/web/20100910193250/http://www.walkinginfo.org/engineering/crossings-enhancements.cfm |date=2010-09-10 }}, retrieved 23 June 2010</ref> Some curb extensions are built with the bike lane passing through (making the extension an island, separated from the main sidewalk by a narrow bike lane).

One study has found that pedestrians crossing at curb extensions have to wait for fewer vehicles to pass before a motorist yields to allow them to cross. The study was too small to determine whether other measures of effectiveness were significant, such as percent of pedestrians crossing after a motorist yields.<ref>{{cite web |title= Pedestrian Safety Impacts of Curb Extensions: a Case Study |author=Randal S. Johnson |date=July 2005|url=http://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/PedestrainSafetyCurbExt.pdf?ga=t |accessdate=5 August 2011}}</ref>

Poorly designed curb extensions can pose a hazard to [[cyclist]]s, as they force cyclists from their position at the road side (or in a roadside [[Segregated cycle facilities|bike lane]]) into the narrowed gap. They can also damage vehicles if the curbs extend too close to traffic lanes.<ref>Albany Times Union "MOTORISTS TAKE HIT ON ROAD PROJECT" July 19, 2004, [https://web.archive.org/web/20120306101527/http://albarchive.merlinone.net/mweb/wmsql.wm.request?oneimage&imageid=6245046] retrieved 29 June 2010</ref>

Author [[Randal O'Toole]] argues that curb extensions are used to discourage the use of automobiles by reducing the number of lanes available for automobiles. In particular, curb extensions can be used to block turn lanes, forcing turning vehicles to remain with the forward moving traffic.<ref>Randal O'Toole "Gridlock"</ref> Curb extensions do prevent drivers from using parking lanes or shoulders as right turn lanes.

However, reducing the crossing distance also reduces the time needed to cross the street. This allows a reduction in the length of the pedestrian phase at signalized intersection, and reduces the time needed to yield to pedestrians at stop sign controlled intersections. This at least partially compensated for any loss in vehicle capacity.<ref>"Road Diets: Making Streets Slim Down Is Good For Pedestrians, Businesses And Even Traffic," Planetizen, http://www.planetizen.com/node/44645</ref>

Curb extensions complicate drainage. They obstruct the gutter, so a catch basin is needed at the uphill end to keep a puddle from forming. An alternate solution is placing a gap in the curb, allowing the stormwater in the gutter to irrigate a [[rain garden]] or [[bioswale]] in the curb extension.<ref>Sustainable Stormwater Management, http://www.portlandonline.com/BES/index.cfm?c=34598, retrieved 28 April 2010</ref>

[[Image:Curb extension Bwy & 33 St jeh.jpg|thumb|Broadway at 33rd Street, [[Manhattan]].]]

To facilitate [[street sweeper|street sweeping]], the internal and external curvatures of the extended curb section are moderately graduated.

Retroactively adding curb extensions to older, established communities has been controversial in some instances, due to the installation of the extensions reducing the availability of on-street parking for some properties, particularly in cases where the curb extension has been installed on its own and not in conjunction with a crosswalk.