Without TransDEM, you need to be sure the 2 routes are within 100 or less of an elevation difference. in the route config, you should see this:
Code:
world-origin {
latitude 38,53.4,1
longitude 77,1.2,-1
altitude 0
}
You can manually change altitude by 100 but not more than that. Check the height of the areas in Surveyor where you would like to merge, if 100 or less, figure the difference and modify one route config accordingly.