Should I downshift in order to slow down my car?

The Dart was refreshed for 1970 with front and rear changes designed to bring the car closer to the design themes found in Dodge’s full-size vehicles through grille and contour changes. In the rear, the Dart’s new rectangular tail lights were set into a wedge-shaped rear bumper design continuing the angled trailing edge of the new deck lid and quarter panels. The revised rear styling cut trunk space almost in half compared to the 1969 model. 14-inch wheels became standard equipment, and the 170 in³ Slant-6 was replaced by a larger 198 in³ version for improved base-model performance and greater manufacturing economy (since the 198 shared a block with the 225, while the 170 had used its own block). Changes to the fuel system improved driveability, economy and emission control. Part-throttle downshift was added to the 8-cylinder automatic transmissions. In compliance with FMVSS 108, sidemarker lights and reflectors were installed at all four corners.