Pack your jerry cans and ready the war rig for a trip to Gastown, average fuel economy is down in the US.

As the government has pushed for ever-higher corporate average fuel economy ratings, we've seen automakers respond with the development of smaller cars with smaller engines as well as hybrid and electric drivetrains. The result of this has been a sizable year-over-year increase in average fuel economy, until now.

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Gas is relatively cheap at the moment, with the average gallon of regular costing around $2.50. Cheap gas means people are thinking less critically about fuel economy in their new vehicle purchases, and when that happens, automakers sell a whole lot more SUVs and crossovers. According to data from the University of Michigan Transportation Research Institute (UMTRI), US average fuel economy is down by 0.2 mile per gallon, to 25 mpg.

Overall, new vehicle sales are down by 5 percent, with cars off by a staggering 17 percent. Light trucks are up, as are crossovers with sales bumps of 5.8 percent and 2.2 percent, respectively. It remains to be seen if this trend will continue as it did in the early aughts, and whether the Trump administration's policy of relaxing environmental regulations will cause average fuel economy numbers to slip further.

On the whole, since UMTRI began studying average window sticker fuel economy in 2007, it's gone up by 4.9 mpg, showing that putting a little bit of fear into manufacturers seems to be working.