What particular factor contributes significantly to fuel conservation?

Combining errands into fewer trips is a significant factor in fuel conservation because it optimizes the use of the vehicle, reducing the overall mileage driven. By grouping errands, the vehicle operates more efficiently and minimizes the number of cold starts, which consume more fuel when the engine is not warmed up. This practice reduces the total distance traveled and helps to maintain a consistent speed, which is generally more fuel-efficient than making multiple short trips that require frequent stops and starts.

The other options, while they may have some effect on fuel consumption, do not contribute as significantly to conserving fuel as combining trips. Frequent acceleration generally leads to higher fuel consumption because it requires more energy and increases wear on the vehicle. Driving with windows down can increase aerodynamic drag, especially at higher speeds, potentially leading to higher fuel consumption. Avoiding the use of air conditioning can save fuel, but its impact can vary depending on driving conditions and vehicle models. In contrast, combining errands consistently proves to be a more effective strategy for enhancing fuel efficiency.