Fuel Use and Legal Limits on a Delivery Run
You drive a light van for a small company on a 220 km round trip, mostly motorway and some town. The van's handbook gives consumption of 8.0 l/100 km at a steady 90 km/h and 10.5 l/100 km at 130 km/h. Your route has a 130 km/h motorway section of 150 km and a 70 km urban section. Roof bars are fitted but unused. Tyre pressures are 0.4 bar below the recommended figure. The van is loaded to about 80% of its payload. Fuel costs 2.80 BGN per litre. Your employer asks whether driving at 130 km/h saves enough time to justify the fuel.
1. Estimate the fuel difference between driving the motorway section at 90 km/h and at 130 km/h, and the time saved.
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At 90 km/h over 150 km: 150 × 8.0/100 = 12.0 l. At 130 km/h: 150 × 10.5/100 = 15.75 l. Difference = 3.75 l, costing 3.75 × 2.80 = 10.50 BGN per trip.
Time: 150/90 = 1.667 h (100 min); 150/130 = 1.154 h (about 69 min). Time saved ≈ 31 minutes.
So the higher speed saves roughly half an hour on this section at the cost of about 10.50 BGN and extra emissions. Whether that is worth it depends on the purpose of the trip, but the fuel penalty is real and predictable.
2. Which factors in the setup are avoidable inefficiencies, and what would you change?
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Three avoidable factors. First, the unused roof bars: they add aerodynamic drag, especially at motorway speed, and should be removed when not needed. Second, tyres 0.4 bar below recommendation: under-inflation raises rolling resistance, increases fuel use and heat, and wears tyres faster - correct them to the handbook figure when cold. Third, speed: 130 km/h costs about 3.75 l more than 90 km/h on the motorway section, as calculated.
Correcting the tyres and removing the bars reduces consumption at any speed; moderating speed gives the largest single saving. The 80% load is normal use, not an inefficiency. A sensible plan is correct pressures, no roof bars, and a steady speed near the legal limit for the road rather than the maximum the van can do.