
I have often found when a puppy startles about something in the early days on a walk (often busses, lorries etc here), I have found standing still for a short time without fussing them to let them process it, and then matter of factly walk on encouraging with a jolly hockey sticks voice.
If they have dug in, then lift them up for a few steps and then put them back down continuing to walk.
Try and keep them always on the side away from traffic but in the direction it is coming from, so things do not come from behind.
I often carry a pup part way anyway, as we usually are going out for longer than the 5 minutes per month of life, with the other dogs.
At 16 weeks her formal walks should be roughly 20 minutes or a mile.