GPS is wonderful, except is doesn't understand that Bay Area traffic can be terrible.
The most direct route from the North, South and West to Just Trains is from the Interstate 680 (I-680) and State Route 4 (SR-4) interchange, head east to the Solano Way exit.
Sadly, most weekdays after 3 pm, this route is impacted by East Contra Costa commute traffic. When this happens, there are some alternate routes (aka: the back ways) that we use to get to the store.
From the North (Benicia Bridge, Fairfield, Vallejo):
On I-680 South, take exit 54 at Arthur Rd / Pacheco Blvd (second exit from bridge). At the end of of the off ramp, turn right onto Arthur Rd. Straight through the intersection (traffic signal) of Arthur Road and Pacheco Blvd, this will put you on Pacheco Blvd. Continue 1.3 miles on Pacheco Blvd to Blum Road (traffic signal). Make the left turn onto Blum Road, and proceed .3 miles. After passing under I-680, turn right on Imhoff Drive. Proceed 1.1 miles to the store, on your right after passing over Walnut Creek.
From the South (Walnut Creek, Oakland, Danville, Pleasanton):
On I-680 North, take exit 50 to State Route 242 (SR-242) toward Pittsburg. Take exit 2 Grant St / Solano Way from SR-242. At the end of the ramp, turn left onto Grant St. After passing under SR-242, Grant St. becomes Solano Way. Continue on Solano Way 1.6 miles to Imhoff Drive (after passing under SR-4). Turn left on Imhoff Drive, the store will be on your left, turn into the parking lot at the end of the divided road.
From the West (Martinez, Crockett, Pinole):
On SR-4 East, Take exit 12A at Pacheco Blvd, on to Muir Road. Turn left at Pacheco Blvd (traffic signal). After passing under SR-4, turn right onto Blum Road, and proceed .3 miles. After passing under I-680, turn right on Imhoff Drive. Proceed 1.1 miles to the store, on your right after passing over Walnut Creek.