View source for Time-saving bias

{{Short description|Cognitive bias}}
'''Time-saving bias''' is a concept that describes people's tendency to misestimate the time that could be saved (or lost) when increasing (or decreasing) [[speed]].<ref>{{Cite journal |last=Svenson |first=Ola |date=1970 |title=A functional measurement approach to intuitive estimation as exemplified by estimated time savings. |journal=Journal of Experimental Psychology |volume=86 |issue=2 |pages=204–210 |doi=10.1037/h0029934 |via=American Psychological Association}}</ref>{{sfn|Peer|2010a}}

In general, people underestimate the time that could be saved when increasing from a relatively low speed—e.g., {{convert|25|mph|km/h|abbr=on}} or {{convert|40|mph|km/h|abbr=on}}—and overestimate the time that could be saved when increasing from a relatively high speed—e.g., {{convert|55|mph|km/h|abbr=on}} or {{convert|90|mph|km/h|abbr=on}}. People also underestimate the time that could be lost when decreasing from a low speed and overestimate the time that could be lost when decreasing from a high speed.

== Examples ==

In one study, participants were asked to judge which of two road improvement plans would be more efficient in reducing mean journey time. Respondents preferred a plan that would increase the mean speed from {{convert|70|to|110|km/h|mph|abbr=on}} more than a plan that would increase the mean speed from {{convert|30|to|40|km/h|mph|abbr=on}}, although the latter actually saves more time.{{sfn|Svenson|2008|loc=Experiment 1}}

In another study, drivers were asked to indicate how much time they felt could be saved when increasing from either a low ({{convert|30|mph|km/h|abbr=on}}) or high ({{convert|60|mph|km/h|abbr=on}}) speed.{{sfn|Fuller|Gormley|Stradling|Broughton|2009}} For example, participants were asked the following question: "You are driving along an open road. How much time do you feel you would gain if you drove for {{convert|10|mi|km|disp=sqbr}} at {{convert|40|mph|km/h|abbr=on|disp=sqbr}} instead of {{convert|30|mph|km/h|abbr=on|disp=sqbr}}?".{{sfn|Fuller|Gormley|Stradling|Broughton|2009|p=14}} Another question had a higher starting speed of {{convert|60|mph|km/h|abbr=on}}, and two other questions asked about losing time when decreasing speed, from either {{convert|30|or|60|mph|km/h|abbr=on}}.

Results supported the predictions of the time-saving bias, as participants underestimated the time saved when increasing from a low speed and overestimated the time saved when increasing from a relatively high speed. In addition, participants also misestimated the time lost when decreasing speed: they generally underestimated the time lost when decreasing from a low speed and overestimated the time lost when decreasing from a relatively high speed.{{sfn|Fuller|Gormley|Stradling|Broughton|2009}}

== Explanation ==
[[File:Time-saving-bias.svg|thumb|Time savings from extra {{convert|10|mph|km/h|abbr=on}} decrease as speed increases.]]
The physical [[formula]] for calculating the time, <math>t</math>, gained when increasing speed is:

<math>t = c D(v_1^{-1} - v_2^{-1})</math>

Where <math>c</math> is constant and used to transform between units of measurement, <math>t</math> is the time gained, <math>D</math> is the distance traveled and <math>v_1</math> and <math>v_2</math> are the original and increased speeds, respectively. This formula shows the relationship between increasing speed and journey time is [[Curvilinear coordinates|curvilinear]]: a similar speed increase would result in more time saved when increasing from a low speed compared to a higher speed. For example, when increasing {{convert|20|to|30|mph|km/h|abbr=on}} the time required to complete {{convert|10|mi|km}} decreases from 30 to 20 minutes, saving 10 minutes. However, the same speed increase of {{convert|10|mph|km/h|abbr=on}} would result in less time saved if the initial speed is higher—e.g., only 2 minutes saved when increasing from {{convert|50|to|60|mph|km/h|abbr=on}}. Changing the distance of the journey from {{convert|10|mi|km}} to a longer or shorter distance will increase or decrease these time savings, but will not affect the relationship between speed and time savings.

Svenson suggested that people's judgments of time-savings actually follow a Proportion [[heuristic]], by which people judge the time saved as the proportion of the speed increase from the initial speed.{{sfn|Svenson|2008}} Another study suggested that people might follow a simpler difference heuristic, by which, they judge the time saved based solely on the difference between the initial and higher speed.{{sfn|Peer|2010b|loc=Study 3}}

It seems that people falsely believe that journey time decreases somewhat linearly as driving speed increases, irrespective of the initial speed, causing the time-saving bias. Although it is still unclear what is the dominant heuristic people use to estimate time savings, it is evident that almost none follow the above curvilinear relationship.

== Consequences in driving ==

Drivers who underestimated the time saved when increasing from a low speed or overestimated the time lost when decreasing from a high speed, overestimated the speed required for arriving on a specific time and chose unduly high speeds, sometimes even exceeding the stated speed limit.{{sfn|Peer|2010a}} Similarly, drivers who overestimated the time saved when increasing from a high speed underestimated the speed required for arriving on time and chose lower speeds.{{sfn|Peer|2011}}

== Consequences in other domains ==

The time-saving bias is not limited to driving. The same faulty [[Estimation statistics|estimations]] emerge when people are asked to estimate savings in patients’ waiting time when adding more physicians to a health care center{{sfn|Svenson|2008|loc=Experiment 2}} or when estimating an increase in the [[productivity]] of a manufacturing line by adding more workers.{{sfn|Svenson|2011}}

== See also ==
* [[List of cognitive biases]]
* [[Amdahl's law]]

== References ==
{{Reflist}}

=== Sources ===
* <!-- {{sfn|Fuller|Gormley|Stradling|Broughton|2009}} -->{{cite journal | last1=Fuller | first1=R. | last2=Gormley | first2=M. | last3=Stradling | first3=S. | last4=Broughton | first4=P. | last5=Kinnear | first5=N. | last6=O'Dolan | first6=C. | last7=Hannigan | first7=B. | year=2009 | title=Impact of speed change on estimated journey time: Failure of drivers to appreciate relevance of initial speed | journal=Accident Analysis & Prevention | publisher=Elsevier BV | volume=41 | issue=1 | issn=0001-4575 | doi=10.1016/j.aap.2008.07.013 | pages=10–14| pmid=19114132 }}
* <!-- {{sfn|Peer|2011}} -->{{cite journal | last=Peer | first=E. | year=2011 | title=The time-saving bias, speed choices and driving behavior | journal=Transportation Research Part F: Traffic Psychology and Behaviour | publisher=Elsevier BV | volume=14 | issue=6 | issn=1369-8478 | doi=10.1016/j.trf.2011.06.004 | pages=543–554}}
* <!-- {{sfn|Peer|2010a}} -->{{Cite journal |last=Peer |first=E. |date=November 2010a |title=Speeding and the time-saving bias: how drivers' estimations of time saved in higher speed affects their choice of speed |journal=Accident Analysis & Prevention |volume=42 |issue=6 |pages=1978–1982 |doi=10.1016/j.aap.2010.06.003 |issn=1879-2057 |pmid=20728651}}
* <!-- {{sfn|Peer|2010b}} -->{{cite journal |last=Peer |first=E. |date=December 2010b |title=Exploring the time-saving bias: How drivers misestimate time saved when increasing speed |journal=Judgment and Decision Making |volume=5|issue=7 |pages=477–488|doi=10.1017/S1930297500001649 |s2cid=18481243 |doi-access=free }} 
* <!-- {{sfn|Svenson|2008}} -->{{cite journal | last=Svenson | first=O. | year=2008  | title=Decisions among time saving options: When intuition is strong and wrong | journal=Acta Psychologica | publisher=Elsevier BV | volume=127 | issue=2| issn=0001-6918 | doi=10.1016/j.actpsy.2007.09.003 | pages=501–509| pmid=17936234 }}
* <!-- {{sfn|Svenson|2011}} -->{{cite journal | last=Svenson | first=O.| year=2011 | title=Biased decisions concerning productivity increase options | journal=Journal of Economic Psychology | publisher=Elsevier BV | volume=32 | issue=3  | issn=0167-4870 | doi=10.1016/j.joep.2011.03.005 | pages=440–445}}

==External links==
* [https://web.archive.org/web/20120422133942/http://www.mpgillusion.com/ The MPG Illusion]

{{Biases}}

[[Category:Cognitive biases]]
[[Category:Time]]