Talk:Stopping sight distance

message: Vehicle mass actually has less effect on braking distances than most people suppose. It actually drops out of the equation. Where
:a = Acceleration (or in this case, deceleration) rate
:F = Force applied
:μ = Coefficient of friction, also called the "drag factor" by police crash investigators
:g = Acceleration due to gravity
:m = Vehicle mass
:N = Normal force, or, in this case, weight
From  Newton's laws of motion and neglecting air resistance:
:Acceleration rate =  mass / force
:: a = m/F 
:Force = coefficient of friction * mass * gravitational acceleration
:: F = μN = μmg 
:Therefore,    acceleration  = mass / mass *coeff. of friction * gravity  
:: a = m/F = m/μmg = 1/μg 
Mass comes back into the equation when designing brakes and tires. Brakes work by converting kinetic energy to heat energy. The more massive a vehicle is, the more energy the brakes must convert. Put big enough brakes and sticky tires on a semi and it will brake like a Porsche. The problem is, they would probably take up valuable cargo room, taking away from the purpose of a truck - moving cargo.
--Triskele Jim (talk) 17:00, 5 June 2009 (UTC)
thread_title: Vehicle mass and braking distances

message: A completely different definition than the one currently given in the lead is given by this book:  That definition is:
:Stopping sight distance for a given design speed is the minimum distance that a vehicle moving at the corresponding running speed will require to come to a safe halt.  It is the sum of the distances traveled during the driver's brake reaction time and during the braking of the vehicle to a stop on a wet pavement.
It appears to me that both this definition and the one in the lead, ascribed to the AASHTO, are somewhat confused; they give the two sides of on inequation between two distances that, for safety, needs to be satisfied. On the one hand there is the sight distance, which is how far a driver can see ahead and spot a stationary condition requiring stopping, such as a boulder on the road. This is independent of the driving speed and the condition of the road surface (except for possible dust clouds on unpaved roads), but may depend on atmospheric conditions. Then there is the stopping distance, which is the distance a vehicle travels from the moment a condition requiring a stop comes in sight until the vehicle actually comes to a halt. This depends on lots of things, such as the reaction speed of the driver, the speed of the vehicle, the condition of its brakes, the condition of the road surface, and the slope of the road. Safe driving requires that the stopping distance always be less than the sight distance. In determining the safe speed limit for a given road, or designing a road for a given speed, assumptions must be made for the reaction speed of a driver and how much a vehicle can decelerate, using safety margins, while the minimal coefficient of friction under realistic conditions may be assumed known. Then it is possible to relate a safe driving speed to a given sight distance, or a safe sight distance to a given driving speed. On a one-lane road with two-way traffic, or a two-lane road where vehicles may use both lanes, the stopping distance must even remain below half the sight distance. I realize that the preceding is all "original research" on my part, but I should hope that there are reliable sources out there that manage to avoid the confusion by giving both sides of the inequation.  --Lambiam 14:09, 26 June 2011 (UTC)
replies: text: One way to handle this is to make a distinction between "available stopping sight distance," which depends primarily on road vertical and horizontal curvature, and "design (or desirable) stopping sight distance," which is based on the prevailing speed, and provides enough visibility so that "the sight distance at every point on the highway should be at least that needed for a poorly performing driver or a poorly equipped vehicle to stop within the available sight distance." (AASHTO Guidelines for Geometric Design of Very Low Volume Local Roads, page 30) --'Triskele Jim (talk) 17:01, 28 June 2011 (UTC)
thread_title:  Definition of stopping sight distance 

message: All the references are from US sources. Other nations may use different values for deceleration, object heights, etc. For example, a documentary I watched years ago said Germany uses 0 mm as the object height for stopping sight distance on the Autobahn, since a pavement defect can cause a crash at those speeds. I don't have anything I can use as a reference, though. --Triskele Jim 16:14, 16 October 2012 (UTC)
thread_title: Globalize

message: Advisory speed limit signs -- those yellow signs often posted where there is a curve in the road -- are often placed there not just to warn drivers of the curve but because there is limited "sign distance," like when the curved roadway is cut through the vertical face of a hill or mountain and you can't see more than 20 feet ahead of you. I know this is outside the subject matter of the article but in California at least, and maybe other states too, police won't ticket you for violating an advisory speed limit sign unless some kind of incident, or accident, occurs. This is just a sore spot of mine cause there is a winding road I travel a lot through with a bunch of blind curves and drivers pay no attention to the advisory speed limits. As dangerous at that road is for cars I've seen bicyclists in packs on that road, and speeding around a blind curve there they are. 2600:8801:BE26:2700:41C1:9981:7CD6:CC06 (talk) 18:38, 14 September 2021 (UTC)
thread_title:  Something I wish could be noted in the article.