The overhead shots made it fairly clear that the road they were driving before they took to the storm basin route was a multi-lane road leading INTO the city proper from the suburban area they came from, so not really an evacuation route in either direction. Once they made the turn the overhead shots showed the lines of vehicles stretching back into the city on the outbound routes and the main highway (which the characters pointedly discussed avoiding). It made some sense, if you're in a hurry to leave the city before everything goes to hell you're probably not going to take the routes filled with stop lights and intersections that only lead to hillside suburbs and more clogged highways, so those roads would be fairly clear once everyone was gone/dead. Kind of like the Atlanta scene in Walking Dead where Rick rode into Atlanta on a deserted side of the highway, while the outbound side was clogged with abandoned cars.
That said, the rest of the episode was the culmination of terrible plot writing that has left me totally soured on Fear the Walking Dead. For starters, how the fuck are Travis and company NOT recognizing that they just essentially murdered not only the military folks in the compound but all those people in the MASH wing, the people in the holding pens where Nick and Strand were, and most of all, every single one of their neighbors on the hill, all of whom are sitting at home with their children blissfully unaware that 2000+ hungry undead are now roaming freely and will soon pour through the gate Travis so conveniently left open for them to feast on everyone inside the safe zone? To save seven people they killed 700, the vast majority of whom were innocent.
Oh, but operation COBALT would have killed those people anyway right? Really? Because the show certainly didn't make that clear in any way. It looked a hell of a lot like the military were simply abandoning the safe zone. Most of the soldiers had already evacuated, and they made a point of showing the last chopper coming to pick up the dozen or so critical patients, the doc, Liza and the remaining soldiers (all of whom were essentially murdered by Mr. Salazar and his brilliant plan to free his already dead wife). So who was going to be left to carry out this "humane extermination" of the safe zone? Who was left to even care? The military was happy to leave an arena full of 2000+ walkers just sitting there, do they really give a shit about another 600 or so live people who might become walkers at some point or another?
Which brings me to the most glaring issue with the events of this episode...WHERE THE FUCK IS EVERYONE? All of L.A. could not possibly have fit inside that arena, and the soldier specifically mentioned the number was only in the 2000 range. The line of abandoned cars leaving L.A. speaks to the sort of mass exodus we saw in Atlanta in the original show, only in the original show there are walkers EVERYWHERE. In this show, the sum total of L.A.'s walker community seems to be the 2000 or so in the arena and a handful of stragglers around the streets that the army either missed in their sweeps or they were survivors who turned later. There should be a million or more walkers shambling around every corner of the city, so where did all those people go?
Fear the Walking Dead is a complete and epic failure of storytelling, which is ironic for a channel that uses the motto "Story Matters Here". Instead of the compelling and frightening story we were promised, of how civilization could go from Starbucks to Walking Dead in the matter of a few short weeks, we got a mostly boring and one-dimensional tale of a family that gradually wakes up to the horror of the apocalypse happening around them while making ridiculously stupid decisions along the way, and we had the middle and most interesting part of that story conveniently cut out, leaving us with bookends of stupidity that tell a completely unsatisfying story about characters we could care less about. They even killed off the only sympathetic character of the bunch to end the season, though I have high hopes for Strand now. It's obvious he is not what he seems, and I doubt he actually owns the house or the yacht. If I keep watching next season, it will be the mystery of Strand that brings me back, and the curiosity of what the plan is for the yacht.