Why The Same Car Drinks More In Karachi Traffic Than On The Motorway

One Month, One Car, Two Averages

One car, one driver, one month, two averages that look like they belong to different vehicles. Split by trip type, my sedan's log for that month reads 10.10 L/100km on city errands and 5.87 L/100km on motorway runs. The city figure is 72 percent higher than the motorway figure, and nothing was wrong with the car on any of those days. The route was the difference, and the route is usually the difference when a car appears to miss its advertised average.

The log came from a month when I was already keeping fill-to-fill records for another reason, and I split the notebook afterward out of curiosity. City driving that month totaled 612 kilometers on 61.8 liters, mostly Multan errands, school runs, bazaar trips, and the slow geography of a working week. Motorway driving totaled 1,360 kilometers on 79.8 liters, two Lahore round trips and nothing else. Blended, the month reads 7.18 L/100km, a number that describes neither kind of driving and satisfies nobody who quotes it.

The average speed row is the tell. In the city the car averaged 14 kilometers an hour across its engine-on time. On the motorway it averaged 96. Fuel consumption is priced by distance, but the engine is paid by the hour, and a car spending its hours at 14 kilometers an hour spreads each liter over very little road. Every mechanism in the next section is a variation on that sentence.

Where The City Fuel Goes

Start with the stops. A city kilometer in Multan holds a dozen events a motorway kilometer never meets: signals, rickshaw gaps, speed breakers, the slow merge at every chowk. Each stop throws away the car's momentum, and momentum is stored fuel. Accelerating back to 40 kilometers an hour costs the energy the brakes just burned off as heat, and the city asks for that payment every few hundred meters. The converter on this page can translate the resulting figure into any unit you like, but no unit makes the bill smaller.

Then there is idling, the city's quiet tax. At a standstill the engine burns fuel to produce zero kilometers, and every minute of it lands directly in the L/100km figure, because the distance side of the fraction does not move while the fuel side keeps counting. Long signal phases, a queue outside a school, ten minutes waiting with the air conditioner running outside a shop: none of it feels like driving, and all of it is in the average.

Cold starts take their share too. Most city errands are short, and a short trip runs entirely on a cold or warming engine, which burns richer and works harder than a settled one. The motorway trip pays its cold-start cost once and then amortizes it over 340 warm kilometers. The school run pays it every single morning for a three kilometer trip. Same car, same engine, and one of them never gets to be the efficient machine it is on the open road.

Air conditioning finishes the pattern. The compressor draws its power whether the car is moving or not, so at city speeds its cost lands on very few kilometers, while at motorway speed the same hourly cost spreads across six times the distance. This is why the gap between my two averages is not a fixed property of the car. It is a property of where the car spends its hours, and it widens or narrows with the city, the season, and the driver's diary.

The Motorway Number Is Real, And It Is Not The Whole Car

None of this makes the brochure figure a lie. The EPA runs separate city and highway test cycles and publishes both ratings, because it knows the same vehicle produces two different honest numbers in the two environments. A brochure usually leads with the combined or the kindest figure, and a seller quotes the best number the car ever produced, which is nearly always a motorway-flavored one. When your car then returns 10 L/100km in city weeks, the gap feels like a defect. Mostly it is a category error: a highway number held against a city life.

After that month I stopped answering the average question with one number. I quote two averages or I quote none, because the single blended figure misleads everyone who hears it, starting with me. That rule, learned from one notebook, is the one I now give every driver who asks me whether his car has developed a drinking problem.

The practical test for a worried owner is comparison within one category. Judge your city figure against other city figures for the same class of car, and your motorway figure against motorway figures. A sedan returning 5.87 on the motorway and 10.10 in the city is behaving like a sedan. A car whose motorway figure is also poor, on a steady run with a warm engine and sane speeds, is telling you something real, and that is when a mechanic earns his fee.

A car does not have a fuel average. It has a fuel average per kind of road, and the brochure only introduces you to one of them.

Karachi Sits At The Hard End Of This Chart

My log is Multan's version of the pattern, and Multan is not the hardest classroom in the country. Karachi traffic stretches every mechanism in this article: longer idle phases at signals that gridlock for whole cycles, average speeds on bad corridors that fall below my 14 kilometers an hour, sea-level heat that keeps the air conditioner working at full draw, and trip chains where the engine cools between stops and pays the cold-start cost again and again.

A Karachi driver reading my 10.10 city figure and finding 11 or 12 in his own log is not necessarily driving a worse car. He is driving the same physics in a harder city.

The hybrid question grows directly out of this gap, because electric assistance attacks exactly the city's costs: the stops, the crawls, the idle minutes. Whether it attacks them enough to justify an imported hybrid's price is a numbers question, and The Hybrid Decoding works it with a real auction figure and a real street measurement rather than a brochure promise.

Quote Two Averages Or Quote None

The use case this article exists for is the owner standing in a workshop or a family argument, asking whether the car or the route is at fault. The log answers it in one page. Split a month of fill-to-fill records by trip type, the way the table at the top of this article does, and compare like with like.

If both split figures sit in the normal band for the car's class, the route is at fault, and no repair will fix geography. If the motorway figure itself is swollen, the car is talking, and it deserves a hearing.

What remains is the small print of daily driving: tire pressure, roof loads, air conditioner habits, the weight in the boot. Each moves the figure by a little, and together they move it by enough to matter across a year. I spent a later month changing one variable at a time on my own commute, and The Results Of That Experiment rank which of them deserve your attention and which were noise. Start with the split log, though. Until you know which of your car's two lives you are measuring, every other number is a guess wearing a uniform.