You need to learn somewhere quiet to practice changing gear, using the brake and accelerator, before you could put all these behaviours together when your instructor takes you on a main road, let alone a busy motorway.
To minimise potential triggers, we need to teach our dog that there is a positive outcome to being in a wide range of environments. Sometimes an unexpected off-lead dog or a person appearing out of nowhere can derail your training. So, make sure you and your trainer have a strategy for these situations to get you and your dog out of there safely.
Otherwise, as Sarah Whitehead says, ‘it’s like taking a learner driver onto the M25 after just a couple of lessons and expecting them to act like an experienced driver’.