how about if the trip lines were gradients instead of solid lines?
two colours could be chosen, one for the start of the trip and one on the opposite of the colour spectrum for the end of the trip, so that when a trip has a few photos on it, you can tell where it began more easily and also you can basically track where you had travelled just by the gradient. a key could be used to explain to people.
for example, green for the start of the trip gradually changing to red for the end of the trip.