My Opinion; Plan where you want to go, Look at the traffic in the area you wish to travel, Observe the traffic in front and behind and on side of you, Look for several potential positions you can merge into, Begin to accelerate to match the traffic speed to easily blend into the speed of the traffic, Use actual observations (look over your left shoulder, try to make eye contact) and use your mirrors, Use your directional signals, merge into traffic. NOTES: You may have observed a potential place to merge but have an alternative plan if that merge spot is not there and please DO NOT STOP on an entrance ramp. Always drive defensively and watch everywhere, often.
Because it blocks traffic and a vehicle might rear end it if the other vehicle can't brake in time, or other vehicles will be tempted to pass the slow moving vehicle in places when you are Not supposed to pass other vehicles and cause an accident.
It indicates a slow moving vehicle, which would be operating below normal traffic speed.
ask the cop
No. They were not travelling at a safe speed and did not have control of their vehicle.
See 22517 California Vehicle Code: "No person shall open the door of a vehicle on the side available to moving traffic unless it is reasonably safe to do so and can be done without interfering with the movement of such traffic, nor shall any person leave a door open on the side of a vehicle available to moving traffic for a period of time longer than necessary to load or unload passengers."
Yes. You have to be traveling with the flow of traffic. A bicycle is considered a vehicle therefore all the same moving laws of a car apply to a bicycle while on the road.
When stopped and a possible hazard to traffic on the roadway, or when moving so slowly that you are a hazard to overtaking traffic.
So-called "moving" tickets, yes.
Speed X journey time. (Time actually moving).
This is known as the Doppler effect. The pitch changes as the vehicle stops moving towards you, and starts to move way from you.
Radar or LIDAR (laser measurement of speed) has to be directed toward or away from the path of a moving vehicle, as it measures the speed vector between the measuring device and the vehicle. Traffic radar or LIDAR will not measure the speed of a vehicle moving at a right angle to the direction it is pointed.
The sidewalk is usually smoother and designed for walking. You also don't have to worry about moving out of the way of vehicle traffic.