It takes 1 hour to drive from mountain view to san Francisco at about 70 miles per hour. So the distance between mountain view and san francisco is 1 hour x 70 miles / hour = 70 miles.
I have noticed that cars are usually 100 feet away from other on average when there is no traffic. Assuming there is no traffic in the highway now and all cars in the highway are keeping a 100 feet distance from each other, the number of cars per lane would be 100 miles / 100 feet. Given 1 mile is equal to ~ 5300 feet, we can assume the total number of cars per lane is 100 miles x 5300 feet per mile / 100 feet = 5300. There are about 10 lanes (5 southbound, 5 northbound) at any point in the road. Assuming all roads are equally occupied, total number of cars will be 5,300 x 10 = 53,000. Of course this number changes depending on the time of the day. As traffic increases, the distance between cars will reduce and number of cars per lane increases. At certain times of the day, traffic might be high on one side of the highway. In those situations, we will have to calculate the number of cars per side separately.