Reducing speed limits is a key way to reduce speeds, though the precise impact will depend on local circumstances - not just the road environment but also where there associated education and enforcement.
Lower speeds reduce the frequency and severity of road crashes, there is more time to react before any impact, stopping distances are shorter and of course the physical forces involved will be lower. Even where police have not recorded ‘excess speed’ as a particular cause of crashes on a road, these factors mean that lower speed limits can lead to real safety benefits.
Lower speeds reduce air and noise pollution and can encourage steadier, less stressful driving - though badly designed traffic calming schemes can have the opposite effect. Lower speeds help increase people’s perceptions of it being safe to walk or cycle on local roads, which has been a key indicator in road safety policy since 2011. They can help create more liveable communities by reducing severance of traffic flows.
Reducing speed limits can also help reduce street clutter of signs and lines. This may sound counterintuitive at first because, in the past, some traffic calming measures have ruined the look of streets and villages. Best practice has evolved and now authorities are encouraged to reduce signage clutter and use psychological forms of traffic calming - see the improving streets and lanes section. Where speed limits are low, it is easier to justify removing signs or at least making them smaller because drivers will have longer to perceive hazards and because they are travelling slower will find it easier to read signs.