The primary reason days can be warmer on one part of Earth than on another is the angle at which the sun strikes Earth. When the sun's rays hit the Earth at a steeper angle, more solar energy is concentrated over a smaller area, leading to warmer temperatures. Conversely, when the sun's rays strike at a shallower angle, the energy is spread over a larger area, resulting in cooler temperatures.
Other factors, such as the rotation of Earth, can influence temperature variations over a 24-hour period, but the direct cause of differing temperatures at any given time is mainly due to the angle of sunlight. The speed of Earth's orbit and the number of cars on the road are not significant factors in this regard.