Traveling East on Interstate 10 from El Paso: take Highway 118 south at Kent for the 39-mile scenic drive to the observatory. Remember that the Observatory is on Central Time (El Paso is on Mountain Time - one hour earlier than the Observatory).
Traveling West on Interstate 10: take Highway 17 south at Balmorhea to Fort Davis, then Highway 118 north 16 miles following the signs to the Observatory.
From Big Bend National Park: take Highway 118 from Terlingua north through Alpine and Fort Davis to the Observatory. Approximately 112 miles.
The nearest standard fueling stations are in Fort Davis, 15 miles away. There are currently three electric car charging options in the wide area "near" McDonald Observatory. One is at El Cosmico in Marfa, Stable Performance Cars in Alpine, and the Balmorhea Visitors Center. Please check with these providers before making your trip.
There are no fuels available at the Observatory.
The closest commercial airports are El Paso International (190 miles) and Midland International (177 miles). Although you can count on roughly 2.5 to 3 hour drives from either, when driving from El Paso you'll lose an hour going from Mountain time (El Paso) to Central time (McDonald). For private aviation there are airstrips in Marfa and Alpine (both about 40 miles from the Observatory).
Where to stay
Fort Davis is the nearest town to the Observatory and boasts a number of hotels, motels, and B&Bs. The Fort Davis Chamber of Commerce maintains an extensive list of area accommodations. Additionally, the Chamber sites of Alpine (~ 45 miles) and Marfa (~ 37 miles) also list area lodging.