I wondered if he walked/ran along the path by the River Lark. It emerges at the main road by Barton Mills, which you have to cross in order to continue following the Lark towards Mildenhall.
This would fit with the delivery driver's sighting of a man in a pink shirt crossing the main road. Corrie's direction of travel from Flex, to the horsehoe is almost a direct line towards where the towpath begins (in a residential area to the North of BSE). The Barton Mills service station/waffle shack area is a horrible place to cross (I have done it a couple of times) during the day, but perhaps at 4 30 in the morning - not so busy