I checked the website Tor-Einar linked frequently throughout summer and autumn, and (from memory) found:
This is in both directions.
In the event, the very first car that passed me offered me a ride, even without me raising my thumb.
The Icelandic Road And Coastal Administration operates several weather and traffic counting stations and publish the data on their web site. The nearest station is in Kolka, close to Blöndulón a bit further north from where you are going. As you can see from the published data, there is not exactly heavy traffic on the road, only some 120-140 vehicles/day and this includes traffic in both directions. I would not expect there to be substantially more traffic further south near Kerlingarfjöll.
What you also may take into consideration, though unlikely, is that the road is closed. The road is only open during the summer months and will at some point be permanently closed for the winter. I can’t find the closing dates for the last years, but I would guess that the road is usually closed around the beginning of October, if winter comes early, the road will also be closed earlier. It may also be closed on short notice due to bad weather.
Credit:stackoverflow.com‘