What causes a vehicle to not go over 45 mph?

A vehicle may not exceed 45 mph due to several factors, including mechanical issues such as a malfunctioning throttle, transmission problems, or engine restrictions. Additionally, electronic limitations imposed by the vehicle's software, often seen in fleet or rental vehicles for safety, can cap the speed. Other potential causes include low fuel pressure, tire issues, or safety features that engage under specific conditions. Regular maintenance and diagnostics can help identify and resolve these issues.