You mentioned that you have two parents that use the highway. If only one was being habitually late then you would have cause for complaint to them and a reason to charge. When both are late it does support their stories.

I try to be sensitive to traffic issues too in the sense that no matter how early or late a parent leaves work the trip is out of their control. Even the number of red lights they hit along the route can add 10 minutes to the travel time over and above other traffic issues. My furthest parent travel clear across the city so a 40 minute drive approximately and another one that travels across the river into Gatineau so the bridge traffic becomes an issue.