As a bizarre consequence of the failure to switch to metric speed limits, the Department for Transport (DfT) is proposing to raise the motorway speed limit of coaches and buses from 60 mph (96.6 km/h) to 65 mph (104.6 km/h). That’s 4.6 % faster than the 100 km/h maximum speed that their speed limiters allow.
Ironically, the proposal is one of a number of changes actually intended to align motorway speed limits with commercial vehicle speed limiter settings.
Speed limiters are required by law to be fitted to all new heavy goods vehicles (HGVs), and passenger carrying vehicles (PCVs). 90 km/h is the setting used for all HGVs over 3.5 t, and 100 km/h is the setting for all PCVs capable of carrying more than 8 passengers.
In recent years, as older vehicles have gradually been replaced by newer ones fitted with speed limiters, the de facto commercial vehicle motorway speed limit has become 90 km/h for HGVs, and 100 km/h for coaches and buses. As a consequence, it obviously makes sense to review commercial vehicle motorway speed limits and align them with corresponding speed limiter settings.
Yet, rather than opting for the obvious solution of setting commercial vehicle motorway speed limits equal to their corresponding speed limiter settings, the DfT has proposed rounding up to the nearest 5 mph. This means that all commercial vehicles will have motorway speed limits higher than their speed limiter settings. In their consultation document they state,
“it would be unrealistic to align the relevant speed limits exactly with speed limiter settings”.
Presumably, the option of setting speed limits in km/h, the same units that define speed limiter settings, has been overlooked.
Whilst it would be undesirable to have a mix of mph and km/h speed limit signs on our roads, the fact that speed limits for commercial vehicles are not signed means that there is no good reason why motorway speed limits for HGVs and PCVs cannot be defined in km/h, as speed limiter settings already are.
Also, as speedometers are required to show speeds in km/h, as well as mph, drivers of vehicles not fitted with speed limiters should have no problem complying with speed limits in km/h. The ideal solution to the DfT’s conundrum is therefore perfectly practical – commercial vehicle motorway speed limits can be aligned exactly with speed limiter settings.
Of course, having speed limiter settings defined in km/h, as is required by international regulations, means that regardless of how the DfT eventually choose to define new HGV and PCV speed limits, the reality will remain that two different systems of speed measurement are being used on our roads – a situation that can only be satisfactorily resolved by switching to km/h speed limits for all vehicles.
We would therefore recommend that the DfT should as soon as possible initiate a comprehensive plan to complete the switchover to metric units for all road traffic purposes – something that was originally scheduled for 1973, but was postponed in 1970 without a new date being set.
The Department for Transport is inviting comment to their speed limit proposals in a public consultation.
The UK Metric Association’s consultation response can be viewed at the following link:
The consultation remains open until 27 April 2010.
Consultation on Heavy Goods Vehicle and Passenger Carrying Vehicle motorway speed limits.
Speed Limiter Legislation
The Road Vehicles (Construction and Use) (Amendment) (No.2) Regulations 2004
The Road Vehicles (Construction and Use) (Amendment) (No.5) Regulations 2005
House of Commons – Roads (Speed Limit Signs)
9 December 1970 vol 808 cc417-8
UKMA’s leaflet Traffic Signs 2.0, summarising the case for metric signs, can be downloaded by clicking on this link. Alternatively, free printed copies can be obtained by e-mailing email@example.com