Chapter 4.6.5 of the style manual shwos a table with road speeds and its corresponding "highest speeds". I created a small test map with roads of ca. 100 km length of all 5 road_types and added speed limits which translate into the 8 different road_speed codes with the current (v3310) default style. Following table shows my car navigation results on an Oregon 600 with current firmware (3.90): Roadspeed Distance Time Speed Simulationspeed 7 99,9 00:53:27 112,14 254 6 99,7 00:56:41 105,53 130 5 100 01:00 100,00 100 4 99,5 01:16 78,55 90 3 100 01:34 63,83 70 2 99,9 02:03 48,73 50 1 99,6 03:06 32,13 30 0 100 06:09 16,26 16 The "Speed" is calculated by dividing the distance to destination by the time to destination; the "Simulationspeed" is the speed shown on the device when you select the simulation option. The speeds do not depend on the road_type value. The speeds for classes 0, 1, 2, 3, and 7 are multiples of 10mph. When using a different routing type (e.g. pedestrian), the simulation speed did not change (i.e. a pedestrian "walking" at 50 km/h...), but the calculated time to destination changed (i.e. a pedestrian was doing ca 5 km/h, a cyclist ca. 25 km/h). With an Oregon 400 with old firmware (4.20), values are slightly different: Roadspeed Distance Time Speed Simulationspeed 7 99,9 00:45:20 132,22 129 6 99,7 00:51:51 115,37 113 5 100 00:56 105,63 103 4 99,5 01:07 89,10 87 3 100 01:32 65,22 64 2 99,9 02:03 48,73 48 1 99,5 03:06 32,10 32 0 100 10:16 9,74 9 The main difference is in faster speed for higher road_speed types, but lower simulation speed. This means that Garmin uses different speeds for calculating the time to destination between different device types! I hope this information helps the creators of maps, and helps to clarify questions on why this route was taken instead of that...