20 km/h in residential areas? Sinn Fein are mad!

The Dail will vote next week on the introduction of a 20 km/h speed limit in residential areas and housing estates. Sinn Fein proposed this bill and local authorities would – if it becomes a law – decide what roads would be covered by the new limit.
Lowering the speed limit in housing estates is something that will happen at some point and it makes a lot of sense around schools for example, but the speed of 20 km/h is totally bonkers. Had they said 30 km/h I would agree as long as it is only for VERY limited high-risk areas. But it is impossible to drive 20 km/h reliably in a car because the speedometer doesn’t even show anything below 20 km/h in many cars. And if that means it couldn’t be enforced because I would think something the driver can’t control can’t be enforced effectively, then the whole idea is infeasible.
Another crazy Sinn Fein idea!