News

As of January 1, 2007, all vehicles of 3.51 tonnes or over registered between October 1, 2001, and December 31, 2004, will have to be limited to 56mph. This will affect around 40,000 7.5-tonners and as many as 18,000 vans. One year later the same regulations will also be applied to all vehicles over 3.51 tonnes registered after December 31, 2004. To find out how this will affect operators, MT took to the motorway in a 7.5-tonne Daf LF at both the current and new speed limits.

The  test

Our test was conducted on the M40, between kilometre markers 68 and 96. We travelled in both directions between these points, covering a total of 56km at both speeds. There was a strong wind throughout the test, but traffic conditions were excellent, with no hold-ups. First was the 70mph journey, which given the poor weather conditions, was stressful to say the least. Trying to maintain a steady 70mph was difficult with the fully-laden truck being buffeted by strong side winds.

For most of the journey we were able to sit at exactly 70mph with the cruise control engaged, but fell back a few mph on a couple of occasions when slower traffic pulled out in front of us. At the moment 7.5-tonners are allowed in the outside lane of the motorway, but this will be illegal next month for those vehicles fitted with 56mph speed limiters. The journey took 30 minutes and 14 seconds to complete, and the truck consumed 11.92 litres of fuel.

The 56mph test was  a totally different driving experience. The wind had less of an effect at this speed, and we didn't have the hassle of competing with cars for a space in the middle and outside lanes. As a result the overall driving experience was considerably more relaxing. On this occasion the 56km route took 37 minutes and nine seconds, and used 9.033 litres of fuel.

The result

By reducing our speed from 70mph to 56mph we were able to save three litres of fuel - which means that we used 32% more fuel on the faster journey. But what we gained in improved fuel economy we lost in time - the extra seven minutes equating to a 23% increase in journey time. So a driver who does two hours of motorway driving a day will spend an extra 30 minutes at the wheel per shift.

Conclusion

Slowing down from 70mph to 56mph clearly has a major impact on fuel economy. But it isn't just about fuel and journey times, as you also have to take into account the less stressful driving experience. The new speed limits will also result in reduced wear and tear and longer tyre and brake life. It is worth mentioning that this test was the best possible scenario for the 70mph run as there was little on the road and we were able to use cruise control for the bulk of the test.  If the motorway had been more congested then the continual bursts of acceleration to keep up with the traffic would have consumed even more fuel and shortened the time difference. An extra 58,000 trucks will be limited to 56mph next year. Over 56km the Daf LF used 3 litres less fuel at the new lower speed.