JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr1 =
[
{'hour':1,'car':[{'audi':1377},{'bmw':716},{'ford':3819},{'mazda':67},{'toyota':11580},{'tesla':0}]},
{'hour':2,'car':[{'audi':1340},{'bmw':709},{'ford':3420},{'mazda':28},{'toyota':11583},{'tesla':0}]},
];

var arr2 = arr1.map(function(hour, index){
	return hour.car.map(function(car, index){
  	var carName = Object.keys(car)[0];
		return {
    	"car": carName,
      "miles": car[carName]
    }
  })
})

console.log(arr2);