The article mentions that the energy input from combustion is significantly higher than that from insolation in Manhattan in January, but also that the primary driver of the heat island effect is from building materials.
Obviously asphalt roads and (especially) parking lots are an indirect contributor to low-albedo and low-permeability landscape.
Taken together, how much of the heat island effect is due to the automobile? Would a pedestrian + transit city, with aggressive tree canopy, still be a heat island?
Even repainting roofs from black to white can make a major difference for minimal cost.
Planting trees is great in many ways (quality of life and air quality in addition to heat mitigation) but is pricier. It can also take several years to "bear fruit" (even for non fruit-bearing trees ;-) because generally you plant saplings, which can take decades to grow to a size where they provide significant shade. NYC hust completed an initiative to plant a million new trees, and it's barely made a dent in the amount of treeless sidewalks, let alone unshaded space in the city.
It would have been nice if the article had made more concrete recommendations, tho, I agree.
But roofs aren't really important at pedestrian level, I've seen many recent buildings having fixed external blinds, leaving an air gap between glass/concrete which should help draw up the hot air.
Not only do you have thousands of vehicles burning thousands of gallons of petroleum, you also have low-albedo asphalt parking lots everywhere.
Do car-friendly cities have a bigger heat-island effect than transit-friendly cities?