The problem is you burn that gas and put carbon into the atmosphere which warms the planet.
Yeah both use significant energy in both moving the 4000 pounds around and maintaining the millions of miles of highways.
The real win for environment would be building cities and towns to support not having to drive everywhere.
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But only a mini amount, how much energy do we spend making the new car vs maintaining the old one. Young people need opportunity to buy cars as well, but the price jump can be too big for many. My experience with transit around Vancouver is great unless you need to get to the next spoke over, or went for a drink downtown and then have to walk an hour to get home in the evening (not solved by having a car obviously, but a shame there isn't an affordable responsible option after 8pm)