Speed limiters are becoming increasingly popular with van operators who want to make sure their drivers stay within the law when on the road and, perhaps more significantly, keep fuel consumption as low as possible.
Towards the end of last year we let vehicle safety and security firm Cobra fit its E-Cruise digital speed limiter to our Caddy for a month. The device can be fitted and removed without leaving a trace on the vehicle and does not affect the warranty. The driver cannot override the system either.
Wanting to give the system sufficient leeway to make a difference to our fuel consumption, we had ours set at a maximum of 62mph rather than 70mph. Up to the set speed the limiter made absolutely no difference to the van’s performance, so journeys in urban environments were unaffected. Once out on the open road, however, the Cobra system quickly made its presence felt. It could be disconcerting – when accelerating smoothly onto a motorway, for example, it could suddenly feel as if you’d hit an invisible wall, or entered one of those dreams where you try to run but find your legs will only move in slow motion.
Overtaking manoeuvres on single carriageway roads are definitely to be avoided. Bearing this in mind, operators of small vans may be better advised to set the limiter at 70mph if sufficient savings can still be made.
Driving behaviour has to be adapted to become more like that of a trucker, and extra care must be taken when changing lanes on motorways, particularly at Y-junctions where one motorway branches off from another and fast-moving traffic may be approaching from behind.
The fuel savings achieved with our speed limiter were impressive. On an 83-mile loop based mainly on the M20 in Kent with a couple of roundabouts thrown in, we averaged over 56.9mpg with an average speed of 50mph.  When we repeated the route without the Cobra device we managed 38.7mpg with an average speed of 64mph. But while the fuel-saving benefits are obvious, they have to be weighed against increased journey times – our second trip was 24 minutes quicker than our first. This meant we were relieved the speed limiter had been removed by the time our Caddy transformed itself into Santa’s wagon for the long haul up to Loch Lomond in Scotland over Christmas, during which we averaged over 40mpg. Who needs reindeers?