I should go from Bangkok to Chiang Mai tomorrow and return on Tuesday, traveling by bus. Will the roads still be passable or will they already be clogged with the end-of-year exodus?

You will be back five days before the New year begins

I would imagine that those days would be a bit early for the end of year exodus.

From Friday 29th onwards would be the time to avoid.

3 hours ago, Puppa said:

I should go from Bangkok to Chiang Mai tomorrow and return on Tuesday, traveling by bus. Will the roads still be passable or will they already be clogged with the end-of-year exodus?

If you return.  Buses?  They have a sad habit of overturning as opposed to returning.

Nowadays if I'm going to CM <--> BKK i either drive or take a plane. 

Return on 26th should be "normal" (9 to 11 hour ride).

You must be fit to take such a trip within three days on a bus.

3 hours ago, connda said:

If you return.  Buses?  They have a sad habit of overturning as opposed to returning.

Most do make it - but use of single level bus is a lot less stress when rounding a corner or making a U-turn.

The train from BKK to CM, overnight, is enjoyable. Select the bottom bunk, it's a bit wider. I've done it a few times. Just a thought.

On 12/23/2023 at 10:24 AM, Puppa said:

I should go from Bangkok to Chiang Mai tomorrow and return on Tuesday, traveling by bus. Will the roads still be passable or will they already be clogged with the end-of-year exodus?

Should be ok

You are going to have a sore, flat bum when you get back to Bangkok