Why cars in the next lane seem to go faster

The temptation to change lanes on a motorway may be prompted by an illusion.


Switching lanes while driving along a busy road can be a risky manoeuvre. It is often instigated on the driver's judgement that the cars in the next lane are moving faster than those in the driver's own lane. But faulty intuition1,2,3 may cause people to overestimate the speed of vehicles in the next lane, believing that they are moving faster even when both lanes have the same average speed. We suggest that this illusion occurs because more time is generally spent being overtaken (passed) by other vehicles than is spent in overtaking them. Knowing that this effect is illusory might encourage drivers to resist small temptations to change lanes.

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Figure 1: Relation of traffic density to the amount of time spent overtaking and being overtaken.


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Correspondence to Donald A. Redelmeier.

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Redelmeier, D., Tibshirani, R. Why cars in the next lane seem to go faster. Nature 401, 35 (1999). https://doi.org/10.1038/43360

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