How long (time) does it take to drive from Arenal to San Jose on a Sunday?

Absolutelly.

I do it very often.

It takes around 3hr 30mins from San Jose.

The road is in good shape and there is low traffic

Just came from Arenal. It took me about 3 & 1/2 hours from Pavas (near San Jose) to Arenal (La Fortuna). The road is really good at this time of the year. Recommendation, drive early morning when the fog hasn't go down. If you leave at 9 am.. you will be at San Jose, near 1pm. But remember, sometimes that area may have some road blocks due to weather. To be save, better leave a little bit early. Remember that at Costa Rica, no mattter if you are really near, you may whant to leave at least 30 minutes bufore just in case. This comes from myself that I leave hear and love to travel.

You should calculate about four hours to get there. If you're not held up, you might get there a little early, but I assume that's better than being late.

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