If the Contractor wishes to place a mixture that is in transit, under what condition is this allowed?

The option indicating that the Contractor must have the Engineer's approval before placing a mixture that is in transit is grounded in the emphasis on oversight and quality control within roadway construction processes. The Engineer plays a crucial role in ensuring that all work meets specified standards and that the conditions under which materials are used are appropriate for maintaining structural integrity and performance.

This requirement for approval acts as a safeguard, ensuring that any potential issues related to the material's quality, environmental conditions, or compliance with project specifications are addressed before the placement occurs. This is particularly important in maintaining the overall safety and durability of the roadway, as improper placement could lead to significant issues down the line.

The other options suggest varying degrees of autonomy for the contractor that could lead to inconsistent practices, potential safety hazards, or violations of project regulations. Understanding and adhering to the need for the Engineer's approval fosters accountability and ensures alignment with established engineering standards and practices.