"Major" land routes from western VA and eastern, PA were:
North from VA on the "Great Wagon Road" to Cumberland Gap. This road ran from Philadelphia, PA, west to the Cumberland Gap and south through the Shenandoah Valley of VA and on through central NC, SC and on into GA.
The road west from Philadelphia went through the Cumberland Gap. At the Comberland Gap, the main East-West road from Philadelphia to Belmont County, OH met the North-South "Great Wagon Road". This road went on west roughly parallel to modern US 40.
In the early 1800s these roads were both in very poor shape. They were essentially unpaved, narrow, unbridged and very winding.
The east-west road from Philadelphia went through Belmont county, OH. It was upgraded in the 1820s and the 1830s as part of the first Federally fundeded interstate system.
As stated above, it generally went along Interstate 40, through PA, the tip of MD, VA, WV to Wheeling and on into OH. Because of the Federal funding, this road was named the "National Road".
In Ohio, the original section of the road stopped at Zanesville. This section is often referred to as "Zane's Trace" because this part of the road was established by Ebenezer Zane around the 1790s
As an aside, Ebenezer's grandson, Zane Grey, was a very popular western novel writer. Many of his works have been made into movies.
In the later 1840s the National road was improved further west frome Zanesville, along current Route 40 into IN and IL.
All of the above is off the top of my head. There may be some factual errors but the main thrust of my statements is correct.
If your ancestors went west from PA or northern VA by land, they likely followed what later became the National road. You can find a lot of information about both the National Road and the Great Wagon Road on the internet. The national road, in particular probably went exactly where the crude road of 1815 went. There are many books and internet articles, with photos of mile markers, etc. showing exactly where the road went, naming towns along the way.