I'm not sure why this is the case, but American consumers have come to expect (have been trained to expect?) a wide variety of choice at the supermarket. I'm talking like, you want honey? You've got 50 different brands/sizes of honey available. Repeat for every expected type of product, and you need a big centralized building for this to work out economically.
Of course, all problems in NA urbanism seem to stem from land zoning. Building a small grocery store in a residential neighborhood is illegal in a distressingly huge percentage of urban land here, and it's been this way since the 50s. So that's probably part of why the megamart has succeeded. The concept of 'mixed use' is a new idea to many cities, and it's not well distributed on the zoning maps.
The why is because once you have a car, the marginal cost of using the car is only $0.40 to $0.60 per minute of travel. That means if you are running errands, it makes sense to shop at big box stores that can sell for 10%+ cheaper due to efficiencies of scale.
Hence Costco/Target/Walmart/Home Depot/Lowes/Best Buy/Staples/etc succeed over a small business that might be a walkable distance. You are already in the car going to and from work, what difference does a detour make.
You make a solid point, I’d only say you’re overestimating a marginal cost of a minute of travel. Unless you’re doing a long freeway trip (which is unlikely in the context of going to Target), your average speed will be closer to 30 mph. That means that you’ll burn less than 2 gallons of gas (closer to 1 in fact) per hour, and even at today’s gas prices, that will come down to less than $.15/minute. Maintenance and amortization, as a good rule of thumb, are around equal to the cost of fuel, so you’re unlikely to reach $.40/minute, much less $.60, unless you drive expensive, fuel inefficient car at highway speeds for extended periods.
The rest of your comment, however, I fully agree with.
> The standard mileage rate for business use is based on an annual study of the fixed and variable costs of operating an automobile.
I also incorporate morbidity/mortality risks associated with driving, considering it is the riskiest thing people do on a day to day basis which very well could result in loss of income due to not being able to work and other costs.
I also expect inflation to keep driving up replacement cost of cars (and repairs).
Finally, I am under the impression that short distance start and stop driving is more costly via wear and tear than long distance highway driving.
I think they’re overestimating, but more importantly, they also include fixed costs in those figures, while the parent comment was talking about cost of a marginal minute once you already have a car.
I presume that a car would have to be replaced after it is no longer useful, so the replacement cost needs to be amortized over all the miles in the current car.
I think consumers really do make this choice, and aren't very compromising. People have a high expectation for both the variety of products, and the variety of a single product.
As a result, the different people have very diverse diets, and it is unlikely that a small store would satisfy most of them.
For example, each week I shop from 2-3 different supermarkets that are 60k ft^2 each (6k m^2).
And an individual consumer probably doesn't take advantage of all the choices on a weekly basis but in aggregate they do. I have a couple of convenient supermarkets and I don't shop at both weekly but I recognize that each is better for certain things. And Trader Joe's and Whole Foods are even better for others although neither are close enough to make a special trip for the most part.
Of course, all problems in NA urbanism seem to stem from land zoning. Building a small grocery store in a residential neighborhood is illegal in a distressingly huge percentage of urban land here, and it's been this way since the 50s. So that's probably part of why the megamart has succeeded. The concept of 'mixed use' is a new idea to many cities, and it's not well distributed on the zoning maps.