It is easier to notice if you are creeping above 30 mph when travelling in 3rd gear, and this can act as a warning to reduce your speed.

Drivers should choose the appropriate gear for their speed and the road, weather and traffic circumstances, and change gear as those circumstances change. The most appropriate gear to use when driving at 30 mph will depend on your engine size, but in many modern cars it is possible to drive at 30 mph in 3rd gear without making the engine labour.

Practical tips for drivers who find it difficult to stay within the speed limit*

- Check your speedometer regularly

- Know the limits - look for signs

- Assume lamp posts mean 30mph unless otherwise stated

- Speed limits are a maximum

- Try no higher than 3rd gear in a 30

- Give yourself time

*taken from - http://www.rospa.com/roadsafety/adviceandinformation/driving/speed/toptentips/third-gear.aspx