On the way to the Island, they swerve to avoid the body and hit a tree with the truck. After the fight, the aerial view shows the people and truck. There are no tire tracks in the snow from the truck.
Monty and Harper were going to the bunker when Clarke and Bellamy radio them to come to rescue them and they arrive. However. Monty's name was not there on the original list that Clarke had made, as per the new system of drawing lottery to select who remains in the bunker. Clarke and Bellamy were not aware of Jaha's attempt to take over the bunker that Kane prevented from happening, and who remains in the bunker was then being decided by Clarke's list. In any case, what if Monty and Harper had reached the bunker only to find that their names were not drawn in the lottery or were not on the Clarke's list so they have to die. Thus, Even if they had time and resources to go back to the bunker after picking Raven from the island, they couldn't have said goodbyes to Monty and Harper and to Murphy and Emori to make only Bellamy, Clarke and Raven return to bunker for their sure seat. Thus, they were bound to try other method that is why they hat to choose to go to the Ark in Spaceship with Raven's lead. Director presented as if it was a last minute decision based on changed circumstances, but it was not, this was rather the only way left that could have worked. For that matter, they should not have waited to bring Raven on the last hour, they could have done it a day or two earlier.
Kane and Abby are in a closed isolated room collecting names from Arkadia people who are coming one by one giving their name slip. In such a charged environment, how would Arkadia people trust Kane and Abby? There is a possibility that Kane and Abby will just tear off and throw away the name chits of some of the people they don't want to be in the bunker, and put multiple name chits of the person they want to be in the bunker. This, this collection of names should not have been done in a closed room, rather in front of everyone's eyes so that everyone can see that only the name chits submitted by Arkadia people are in the tub.
Marcus and Thelonious use Clarke's list to select their 100 people. However, Clarke, Bellamy, and Raven were on that list, and it doesn't seem that Marcus and Thelonious considered anyone to fill the now open three spots.