Possible Clues:

• Rere?
• Rere of the bridge?
• Made twice as great, and what can be found in the answers to the starred clues
• Rere x 4?
• Re and re times four for the bridge
• Rere, perhaps, times four for the bridge
• Rere or redd?
• Increased fieldwork mostly was in front
• Not the Forth Bridge - the four times bridge, perhaps
• Rere time four?