Satnav systems sometimes send motorists the wrong way but they can also impair their driving ability, according to a study.
Drivers' performance was affected when listening to satnav-style directions in an experiment carried out by Lancaster University and Royal Holloway, University of London.
Volunteers were set tasks by a computer which mimicked the instructions given by a satnav.
The results showed that when people were following complicated satnav instructions they tended to drive faster, with more steering variations, as well as being less likely to notice pedestrians who might be stepping out.
Dr Polly Dalton, from the Department of Psychology at Royal Holloway, said: "What is interesting is that people were able to follow one simple instruction without any significant impact on their driving.
"But as soon as they had to remember a compound instruction, consisting of two sequential directions, we began to notice a difference in their driving ability.
"A lot of effort has gone into designing visually-friendly satnav devices but our research highlights the importance of the way in which the auditory instructions are given."
Dr Pragya Agarwal, from Lancaster University, said: "The results from our research have implications for the way these systems can be designed to be more effective and user-friendly in the future.
"With the increasing reliance on technology for navigation, it is important that such technology is designed so that it supports rather than detracts us from our primary task of driving."