Monday, 14 May 2012

Raising the Speed Limit - Not the Solution the UK Needs

The UK Government is set to announce a consultation about increasing the highway speed limit to 80 miles per hour.  The idea, first floated last September, is meant to contribute to economic growth by reducing losses associated with time spent behind the wheel.  The main justification given by Government ministers for this proposal is that vehicles are much safer than they used to be, more than offsetting any increased safety risk

This is a very curious argument from a government representative, but it's largely beside the point. Speed limits didn't drop in the U.S. and UK because of safety concerns.  They dropped so that those economies could save fuel, and so that motorists could save money.  While road safety advocates can argue the case for and against a higher motorway speed limit, we'll focus on the carbon impact.

As the graph above indicates, higher speeds generally translate into greater fuel consumption, and thus greater greenhouse gas emissions.  This result should be obvious to anyone who has stuck his or her hand out of the window of a moving car.  40% of a car's fuel is used at highway speeds simply to push air out of the way, and the amount of power required to overcome wind resistance increases along the cube of the velocity.  In other words, driving 14% faster (from 70mph to 80mph) will result in much more than a 14% increase in fuel consumption - the actual figure is closer to 20%.  This is bad news for companies and individuals looking to reduce their carbon footprints.

Airlines around the world have already put the Government's claims to the test.  They have tested their customer base and determined that, within limits, fuel savings trump faster arrival times.  Indeed, commercial airliners have been flying 10 mph slower since 2008 in an effort to save fuel.  In the U.S., JetBlue has added two minutes to each flight, saving over $13 million a year on jet fuel.

Even this superficial analysis shows that cutting carbon and saving money go hand-in-hand.  Money saved on fuel can go into hiring staff, purchasing goods and services, and making productive investments.  Increasing the speed limit seems like a very curious way to help the economy.