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Why the plan matters as much as the driving

Most fuel-saving advice concentrates on what you do behind the wheel, but a surprising amount of the saving happens before you turn the key. A cold engine is thirsty. For the first mile or two it runs rich, and the catalytic converter is not yet working properly, so short hops of a mile or two are the least efficient journeys your car ever makes. Do four of those in a week and you have spent a lot of money simply warming up an engine that never got the chance to be efficient.

So the first principle is simple: fewer, longer, better-timed journeys beat lots of little ones. Plan the week's driving rather than reacting to it, and you will cut both fuel use and the time you spend sitting in traffic.

Combine errands into a single loop

Instead of nipping out three times, build one trip that knocks off several jobs. A little thought about the order makes a real difference:

• Do the longest leg first. By the time you reach the shops or the tip, the engine is warm and running efficiently for the rest of the loop.
• Park once and walk. A single parking space in the middle of a high street is cheaper than moving the car three times, and short walks cost nothing.
• Fold the school run into the shopping trip. If you are already out at 3.30pm, do the supermarket on the way home rather than making a separate evening run.
• Use click and collect or a delivery slot for the big weekly shop if it saves you a 20-minute round trip. One delivery van serving 40 households uses far less fuel than 40 cars doing the same journey.

Keep a running list on your phone or on the fridge of things you need, so you are not making emergency trips for a single item.

Time your journeys to avoid the peak

Stop-start traffic is the enemy of economy. Every time you accelerate from a standstill you are burning fuel to move two tonnes of metal, then throwing that energy away on the brakes. In heavy town traffic, fuel consumption can be 30 to 40 per cent worse than the same route driven freely.

If you have any flexibility at all, use it:

• Shift a commute or appointment 20 minutes earlier or later to sit on either side of the 7.30–9.30am and 4.30–6.30pm peaks.
• Do local errands mid-morning or early afternoon, and avoid the school-run window around 8.30am and 3.15pm.
• Treat Friday afternoons, bank holiday weekends and the first Saturday of the school holidays as peak times, because they are.
• Check live traffic before you leave. Five minutes of planning can save 25 minutes of crawling, plus the fuel it would have burned.

Use the sat-nav, but use your head too

A live-traffic sat-nav is one of the cheapest fuel-saving tools you own. Left to its own devices it will reroute you around a jam, and being able to see the next 30 minutes of your journey before you set off is genuinely useful. Two cautions, though.

First, the shortest route is rarely the cheapest. A shorter road through town with a dozen sets of lights, three mini-roundabouts and a level crossing can easily use more fuel than a longer but free-flowing dual carriageway. Second, a hilly shortcut may burn more than a flat detour, because climbing under load is thirsty work. When the sat-nav offers you a diversion, ask whether it is genuinely moving traffic or just moving you onto narrow residential streets where you will stop every 200 yards.

Smooth inputs save more than slow speeds

Once you are moving, the biggest gains come from anticipation and consistency. Look as far ahead as you can, ease off the throttle early for red lights and queues, and let the car roll rather than braking late and then accelerating hard. Aim to keep a steady speed with the lightest throttle opening that holds it, and change up early — around 2,000 rpm in a petrol car is a good guide.

On a flat motorway, cruise control helps you hold a constant speed and avoid the unconscious drift between 60 and 75mph. On hills, switch it off; it will chase the set speed and drink fuel doing it. The sweet spot for most cars is roughly 45–60mph, and dropping from 70mph to 60mph on a long run typically saves around 10 per cent.

Finally, stop idling. If you are waiting more than a minute or two — outside a school, at a long level crossing — switch the engine off. Idling returns exactly zero miles per gallon.

Keep the car ready to save

Planning only works on a car that is in decent shape. Check tyre pressures every month and before any long trip; soft tyres can cost you a few per cent in fuel and wear out faster. Clear the boot of anything you do not need, and take the roof bars or roof box off when they are not in use, because they add drag all year round. Keep up with servicing, especially the air filter, spark plugs and engine oil, and get the wheel alignment checked if the car pulls or the tyres wear unevenly.

Reset your trip computer when you fill up, and note the average mpg for the week. It is a simple habit, but watching that figure nudges your behaviour in the right direction — and it will tell you quickly if the car, rather than your driving, has started to cost you money.