For 2021, Toyota offers only a single engine in the Sienna: a 189-horsepower 2.5L 4-cylinder. The engine comes linked to a CVT transmission and is estimated to deliver 35 mpg in the city and 36 mpg highway. The Sienna is the only vehicle in its class to offer optional all-wheel drive. Toyota's system utilizes a center differential to split power 50/50 between the front and rear wheels under normal driving situations, but it transfers more to the wheels that have traction during slippery conditions. 2-wheel drive Siennas are configured as front-wheel drive. Safety is an important factor in designing any minivan and the Sienna comes with a long list of such features. Standard across the Sienna line is the Toyota Safety Sense Plus (TSS-P) array of safety technology. It includes adaptive cruise control, a frontal pre-collision system (with pedestrian detection and automatic emergency braking), lane departure alert and intervention and automatic high beam headlights. Electronic stability control and anti-lock brakes with brake assist are also standard, as are front seat-mounted side air bags and side curtain bags for all three rows. Driver knee air bags are included as well. Interior accommodations in the Sienna include three rows of seating and the capacity of either seven or eight passengers. LE, XLE, XSE, Limited and Platinum trims span a wide range of equipment, depending on whether the buyer wants simple and basic or luxurious. The base LE does include most popular equipment such as keyless entry, power windows, locks and mirrors, cruise control, 3-zone climate control, Siri Eyes Free iPhone integration, Apple CarPlay and Amazon Alexa compatibility and a 6-speaker sound system. At the top of the range, the Limited adds a premium stereo, 18-inch alloy wheels, Smart Key remote keyless system, a power moonroof, heated seats, automatic climate control system, woodgrain interior trim, a parking assist system and a Bluetooth hands-free calling interface.