In my entire career (lol) I (almost) never arrived too late at school. It happened in my beginning years as a teacher cause I overslept. Well not so strange cause in my younger years I went out more often.
Yesterday I also was too late at school (OK it was just 3 minutes but for me that is too late). It was caused by traffic.
What happened: well I usually need about 15 till 20 minutes to drive from home to school. It is about 10 kilometres (6.25 mile) so not much to worry about. Problem now was the following. Last Monday, when there were ground works in the neighbourhood of my home, they suddenly found an airplane-bomb from WW II. No traffic was allowed in that area. Even the most important runway of Schiphol airport was closed.
When bombs are "touched" this way they can explode within the next 36 hours cause of the delay-mechanism what is build within.
Tuesday morning when I went to work on my normal schedule I did not notice anything at all about closing a specific road. But after driving 5 minutes traffic became a mess. A mess I never had experienced (on this particular road) before.
I thought I would be smart to take some other streets to avoid the most problems but I was not the only one with that thoughts.
What aggravated the problem was a strike in public transport cause bus-drivers want more wages for quite some time now. That also caused that more cars were on the road then usually.

It took me almost 55 minutes to do the 10 kilometres. When you start a day like that the whole day doesn't feel ok anymore. Btw my students didn't made any problem cause of my being too late.