Myth buster: do you really spend 'half' your time driving in town?

Myth: 'I drive mostly in town'

Normal petrol cars get their worst fuel economy in town driving. Hybrids do better there, because they collect energy otherwise wasted when you slow down, then in accelerating can re-use that captured electrical energy instead of burning more petrol. But when speed is roughly constant on faster main roads, hybrid tech does very little to help.

Because of that improvement in urban economy, people say, “half my driving is in town so I should get a hybrid". Usually they’re wrong. Because half the time they spend driving is in town, not half the distance.

Here’s an example – an extreme one but it illustrates the point. On a weekday evening, it’ll take roughly an hour to get from King’s Cross in central London to the southern end of the M1. Then you could drive up the motorway for an hour to Northampton. Simple: an hour each. “Half my driving is in town.”

No it’s not. To the motorway from King’s Cross is seven miles. The motorway section afterward is 63. You’ve done 70 miles. But it was actually 90 per cent motorway, 10 per cent urban. Your fuel consumption will reflect this, as the average will be 90 per cent weighted to the motorway figure.

Many dash displays can give you a graph of the fuel use over the past hour, in say five-minute intervals. They only encourage the fallacy I’m talking about, by overemphasising the periods you’re going almost nowhere and actually using very little fuel. You’d get a more realistic sense of what’s happening if the horizontal scale were distance not time.

Electric cars assume you want more of this info, so they often show a graph of miles per kWh, usually with the same misleading horizontal scale of time not distance.

Anyway, if you did mostly drive in town, you’d be be moving slowly, so would go very few miles in a year. At least unless you were a cabbie or delivery driver and at it full time. If you don’t drive many miles the fuel cost pales beside the finance and insurance.

Time matters when we talk about average speed. It’s distance over time, duh. But it’s completely irrelevant in measurement of fuel economy because that’s distance over volume.