Uphill grades

I-5, the main highway through Seattle, has a peak that occurs near the heart of the city. It's not very high, but the slight upward slope it creates on either side causes traffic to jam up right around the downtown area. This slowdown has always driven me crazy because even if you only have to drive a few miles on the highway, if you pass this area you'll have to tap the brakes and downshift and sometimes sit around for a mile or two before everything suddenly clears up again. All because cars inevitably slow down when they hit an upward slope, causing a Slinky-like compression of vehicles.
This ridiculously fun online traffic simulator allows you to simulate that bothersome traffic pattern. Just click the uphill grade button and wait...and watch the cars pile up. Raise the percentage of trucks and watch things clog up even quicker. Of course, it's not likely that the city of Seattle will be able to flatten the highway out there, so it's just one of those things we'll have to live with.
What's interesting about this traffic simulator is that it teaches you that in certain situations, there is an ideal speed limit to minimize traffic jams. If the speed limit is too low or too high, vehicles move at different speeds which means that it's difficult for some vehicles to change lanes to avoid barriers like lane closings. For example, a truck might not be able to move quickly enough to get one lane over to avoid a lane closing because cars in the free lane are moving too fast.
The other really annoying traffic monkey wrench is the cop who pulls someone over. Everyone slows down when passing the cop, staring at the flashing lights. Does the revenue from that one traffic offender offset the lost productivity from the hundreds of cars which end up stuck in the temporary traffic jam vortex created around the police vehicle?
The other thing this made me realize is that carpool lanes act like lane closings for an arbitrary percentage of the auto population. What a failure carpool lanes ended up being. They didn't change anyone's behavior--I've never met anyone who carpools just so they can use the carpool lane--and simply caused a large percentage of vehicles to have to change lanes, causing jams in the other lanes.
You read the abstracts of all the studies and simulations and papers on traffic and your first impression is that there are a lot of smart people studying this field. But then you end up sitting in traffic the next day, a black cloud rising from your head, and you think it might not be so bad to live in a world like the one depicted in Minority Report, where vehicles are driven by computers and can along the faces of buildings and whatnot, all moving at constant speeds. In exchange for some loss of freedom and control and vehicle feedback you're free of traffic jams.
What this simulation really needs to be accurate is to introduce a conservative driver percentage to simulate all those wussy drivers here in the Pacific Northwest who drive in the left lane at 50mph. In Drivers Ed we were taught that the left lane is the fast lane. Apparently that's not part of the curriculum here.