IAMA Traffic Engineer, AMA
1) Is it faster to weave or to just stay in one lane (if so, which lane)?
Is it faster to go faster? Yes. If you meant 'it seems like I'm stuck behind all these cars and that lane is going faster.' yes, it does seem like it. Page 40 and on of Traffic: (preview available on amazon, great book for any reader btw) does a pretty good job of explaining it. (other note, the USA will never have countdown timers on traffic signals. Edit for clarity: Pedestrian timers are ok, vehicle timers not so much...) tl;dr Queueing theory is hard and it's all in your head.
2) Are left hand turns really that dangerous? Why?
Yes, left hand turns are more dangerous. Imagine cars running randomly though an intersection. OK, maybe you don't have to imagine that. A diagram will show that a car that turns left has many more points of intersection than a right turning one. Each of those dots represents a potential point of collision. Once you start adding more lanes you will have many more points of possible collision. Add in geometry and vehicle shadowing on opposing left hand turns and it makes left hand turns even more dangerous.
3) Would we really be safer if the yellow light was extended for a second?
You wouldn't be safer (assuming that the yellow time is currently correctly timed.) The yellow time is supposed to be timed based on this formula This works out to roughly: 25 MPH -- 3.0 Seconds 30 MPH -- 3.5 Seconds 35 MPH -- 4.0 Seconds 40 MPH -- 4.5 Seconds 45 MPH -- 5.0 Seconds 50 MPH -- 5.5 Seconds 55 MPH -- 6.0 Seconds
If it's a different time, it is probably wrong. The point of the yellow light is to make sure that if you are well ahead of the light that you have time to stop before you get to the stop bar. the point of the red light time is to make sure that if you didn't have time to stop for the intersection that you will clear through the intersection before the green time start on the perpendicular streets. That point where you don't know if you should stop or go? The DILEMMA ZONE.
EDIT: adding more yellow time would additionally be dangerous as people would start to game it and count on it as green time.
4) What causes the seeming random slowdowns on highways?
Call it the butterfly effect. When there is a lot of traffic, a SHOCKWAVE ripples backwards at a certain speed based on traffic speed and reaction time of drivers. The larger ones which involve stops may be caused by a collision well ahead of where you are, but by the time that you get there, everything is gone. A stopped vehicle will reduce the roads capacity to handle that flow of vehicles and will back things up until it is removed. Think of it as putting a hose into a watering can where water comes out the spout just as fast as you are putting it in, a normal traffic scenario. Now, let's take your hand and block a number of the holes at the spout. Water will back up in the can until the holes are unplugged. Now based on the capacity of the spout will traffic clear after it has been backed up.
5) Are toll roads (i.e. turnpikes) designed any better than "free" ones, or are they just faster because there are less people?
Depends on what you mean by better. Turnpikes and interstates are all designed to a certain standard, which in almost every case (USA) is from AASHTO's Green Book. They are in general better taken care of in maintenance based on their steady funding from the tolls, whereas other state roads have to compete with all other state roads for limited funding.
UPDATE: Trafficwaves is a pretty frequent question. I subscribe to this mindset. Slamming on the gas and then brakes is no way to go through life in traffic. give that next guy some room, if someone fills in that gap, give them some room too. maintain a speed in congestion.
UPDATE2: the dutch and their no traffic signals. i guess it works for them in their low volume villages, but im not to hopeful for high volume roads and in 'Murica in general.
UPDATEFINAL: i never thought i would ever get to the front page. lurking is more my thing. lots of fun, and if there was some question buried that i never answered, try a pm. thanks,