When we started making our products, we did a good bit of research on this question and found - as the thread up to this point shows - that here are many experts on this theme who have widely divergent points of view. We consolidated our results and came up with the table below for our Jörðgarð (TM) campaign setting.

Be cautioned. This table probably is no more (or less) accurate than anyone else's. It's just another possibility.

Travel Times Upon the Jörð – 12-Hour Day with Short Pauses

Walking/Miles Walking/Kilometers Horseback/Miles Horseback/Kilometers Landscape
28 45 43 69 Forest Track - Flat
24 39 38 61 Forest Track - Rolling
18 29 27 43 Forest Track - Hilly
9 14 8 13 Forest Track - Mountain
24 39 Horses must be led on foot Forest Path - Flat
18 29 Horses must be led on foot Forest Path - Rolling
9 14 Horses must be led on foot Forest Path - Hilly
5 8 Horses must be led on foot Forest Path - Mountain
30 50 45 72 Open – Flat Track
25 40 40 65 Open – Rolling Track
20 32 30 50 Open – Hilly Track
10 15 15 25 Open – Mountain Track
25 40 40 72 Open – No Trail
20 32 30 50 Open, Rolling – No Trail
15 25 25 40 Open, Hilly – No Trail
8 13 12 19 Open, Mount. – No Trail
28 45 43 69 Prairie, Flat
24 39 38 61 Prairie, Rolling
18 29 27 43 Prairie, Hilly
18 29 27 43 Moderate Swamp, Marsh
9 14 8 13 Swamp, Marsh
4 6 Horses must be led on foot Swamp, Marsh Quicksand
30 50 45 72 Desert, Hard Ground
20 32 30 50 Desert, Soft Ground
5 8 12 (Camel) 19 (Camel) Desert, Sand
20 32 30 50 River ford, to 1 foot /30 cm
10 15 15 25 River ford, to 2 feet/60 cm

Modifiers: Thick undergrowth or brush, - 15%. Frequent potholes, etc., - 50%. Strong river current, -50%. Dodging ranged attacks, -75%.