It's not the shortest or fastest route, but if you're going that way, Artois CA is halfway. Oddly enough, it's also on I-5 southbound.
Independence, California is about the halfway point.
Las Vegas is generally considered the halfway point between Salt Lake City and Las Vegas.
Las Vegas
The pacific ocean
The halfway point between Las Vegas, Nevada and Marcellus, Michigan is Cornell, Nebraska.
Groom, Texas is the halfway point between Northport, Alabama and Las Vegas, Nevada. Please see the related link for Meetways, a site providing halfway point information.
A flight from Las Vegas, Nevada to Seattle, Washington would about an hour, there is approximately 871 miles between the two locations.
1,260 miles
Roughly halfway between Flagstaff and Las Vegas
Las Vegas
Amarillo, Texas is midway between Thibodaux LA and las Vegas Nevada
Kingman