in compression ratio and stronger engine internals. The supercharger is engaged on-demand by an electromagnetic clutch, based on input from the engine management system computer (the Engine Control Unit, or ECU). Previas have optional dual moonroofs: A power horizontal-sliding only glass moonroof above the middle row of passengers, and a pop-up glass moonroof above the front seats. Previas were also the first van to pass all US safety standards as pertaining to front impact, driver airbag, passenger airbag, center-mounted brake light, ABS, daylights, etc. Fuel efficiency is below average (11–13 L/100 km or 18.1–21.4 mpg city, 10–11 L/100 km or 21.4–23.5 mpg highway); the small four-cylinder engine needs to work a bit harder owing to the power to weight ratio of the vehicle, compared with today's 6-cylinder engines. The addition of the supercharger slightly improves power and gives better fuel consumption. The Previa gives a practically panoramic view, excluding the pillars behind the front doors. This also turns the van into a greenhouse, accumulating extreme heat in a short period of time, although solar control glass later became an option, to help alleviate the problem. Previas are affectionately called "eggvans", "eggs" or "beans", because of their shape. In Australia, they have been referred to as "Wombats", because they somewhat resemble the marsupial of the same name. In New Zealand, they are very popular with freedom campers and are referred to as "Bucky" buses. In the United States, the first generation Previa model variations, in order of lowest to highest price/option features, are: DX, DX All-Trac, DX S/C, LE, LE All-Trac, LE S/C, LE S/C All-Trac (where S/C = Supercharged and AllTrac = 4WD) The front passenger seat and a section of floor pan must be removed to perform a tune up because there is not enough room to remove spark plug leads or spark plugs. When the Insurance Institute for Highway Safety tested the 1996 model in the offset frontal crash test, it revealed many safety problems: the cabin structure was unstable, the steering wheel moved upward all the way to the windshield, the lap belt tore which allowed the dummy to end up in a partially reclining position, and there were high forces on both of the lower legs, in which the IIHS evaluated it "Poor". In some countries (mainly Australia, Japan and the United Kingdom), unsold Estimas and Lucidas were re-badged as 1995/1996 Previas. Second generation (XR30/XR40; 2000)