Editing Traffic light (section)

== Effects ==
Drivers spend on average around 2% of journey time passing through signalised junctions.<ref name=":4">{{Cite web|title=Why traffic lights are pollution hotspots|url=https://www.weforum.org/agenda/2015/02/why-traffic-lights-are-pollution-hotspots/|access-date=19 December 2021|website=World Economic Forum|language=en}}</ref> Traffic lights can increase the traffic capacity at intersections and reduce delay for side road traffic, but can also result in increased delay for main road traffic.<ref>{{cite web|date=September 2007|title=Traffic Signals|url=http://www.ite.org/safety/issuebriefs/Traffic%20Signals%20Issue%20Brief.pdf|url-status=dead|archive-url=https://web.archive.org/web/20090327022232/http://www.ite.org/safety/issuebriefs/Traffic%20Signals%20Issue%20Brief.pdf|archive-date=27 March 2009|access-date=1 April 2009|publisher=Institute of Transportation Engineers}}</ref> [[Hans Monderman]], the innovative Dutch traffic engineer, and pioneer of [[shared space]] schemes, was sceptical of their role, and is quoted as having said of them: "We only want traffic lights where they are useful and I haven't found anywhere where they are useful yet."<ref>{{cite news|author=David Millward|date=4 November 2006|title=Is this the end of the road for traffic lights?|work=The Daily Telegraph|url=https://www.telegraph.co.uk/news/uknews/1533248/Is-this-the-end-of-the-road-for-traffic-lights.html|access-date=1 April 2009}}</ref>

A World Economic Forum study found that signalised junctions are linked to higher rates of localised air pollution. Drivers accelerate and stop frequently at lights and as such peak particle concentration can be around 29 times higher than during free-flow conditions. The WEF recommends that traffic authorities synchronise traffic signals, consider alternative traffic management systems and consider placing traffic lights away from residential areas, schools, and hospitals.<ref name=":4" />

The separation of conflicting streams of traffic in time can reduce the chances of right-angle collisions by turning traffic and cross traffic, but they can increase the frequency of rear-end crashes by up to 50%.<ref name="CRF">National Cooperative Highway Research Program, Crash Reduction Factors for Traffic Engineering and Intelligent Transportation System (ITS) Improvements: State-of-Knowledge Report, November 2005, Table 3</ref> Since right-angled and turn-against-traffic collisions are more likely to result in injuries, this is often an acceptable trade-off. They can also adversely affect the safety of bicycle and pedestrian traffic. Between 1979 and 1988, the city of [[Philadelphia]], Pennsylvania, removed signals at 199 intersections that were not warranted. On average, the intersections had 24% fewer crashes after the unwarranted signals were removed.<ref name="CRF" /> The traffic lights had been erected in the 1960s because of since-resolved protests over traffic. By 1992, over 800 traffic lights had been removed at 426 intersections, and the number of crashes at these intersections dropped by 60%.<ref>{{cite web|url=http://articles.philly.com/1992-04-19/news/26003417_1_traffic-signals-traffic-lights-slow-traffic|archive-url=https://web.archive.org/web/20150404015508/http://articles.philly.com/1992-04-19/news/26003417_1_traffic-signals-traffic-lights-slow-traffic|url-status=dead|archive-date=4 April 2015|title=Archives - Philly.com|website=[[The Philadelphia Inquirer]]}}</ref>