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Exactly. Design speed of a highway has mostly to do with its geometry as outlined in AASHTO Policy on Geometric Design of Highways. If you get your hands on it and you are able to understand the geometric requirements you would see that the majority of our highways are either already designed for speeds above 80km/hr or can easily be upgraded to that it is. Some locations may need to have reduced speed limits of 80km/hr (I'm thinking like the bend by Gasparillo flyover)Nissan12 wrote:Slartibartfast wrote:Please tell me, exactly how do you "engineer" a road for a certain speed limit? Once you can answer that you will see why anybody that mentions that as a point against a higher speed limit is speaking utter rubbish. If you want to talk about safe highway speeds given the current wearing surface due to weathering, wear and tear and faulty construction then that is a different point and would only be applicable to specific locations of the highway inspected for such. Otherwise, please stop the spread of misinformation. It makes it worse for ussMASH wrote:i thought the roads aren't engineered to be safe above 80kmph?
could really remember a lot of words read about the engineering.
All physics (but hopefully some civil engineers here will chime in) horizontal curves and cross fall to counter centripetal and centrifugal forces, vertical curves for visibility and stopping distance based on speed.... Yeah, not just making a foundation and paving it...
AASHTO - A POLICY on GEOMETRIC DESIGN of HIGHWAYS and STREETS 2001 wrote:SPEED
The speed of vehicles on a road or highway depends,
in addition to capabilities of the drivers and their vehicles, upon four general conditions: the
physical characteristics of the highway and the amount of roadside interference, the weather, the
presence of other vehicles, and the speed limitations (established either by law or by traffic
control devices)....
Design Speed
Design speed is a selected speed used to determine the various geometric design features of
the roadway. The assumed design speed should be a logical one with respect to the topography,
anticipated operating speed, the adjacent land use, and the functional classification of highway....
The selected design speed should be consistent with the speeds that drivers are likely to
expect on a given highway facility. Where a reason for limiting speed is obvious, drivers are more
apt to accept lower speed operation than where there is no apparent reason. A highway of higher
functional classification may justify a higher design speed than a lesser classified facility in
similar topography, particularly where the savings in vehicle operation and other operating costs
are sufficient to offset the increased costs of right-of-way and construction. A low design speed,
however, should not be selected where the topography is such that drivers are likely to travel at
high speeds. Drivers do not adjust their speeds to the importance of the highway, but to their
perception of the physical limitations of the highway and its traffic....
Where the physical features of the highway are the principal speed controls and where most
drivers choose to operate near the speed limit, a design speed of 120 km/h [75 mph] would serve
a very high percentage of drivers....
...On many freeways, particularly in suburban and rural areas, a design speed of 100 km/h
[60 mph] or higher can be provided with little additional cost above that required for a design speed of 80 km/h [50 mph]....
...Isolated features designed for higher speeds would not necessarily encourage drivers to
speed up, although a succession of such features might. In such cases, the entire section of
highway should be designed for a higher speed. A substantial length of tangent between sections
of curved alignment is also likely to encourage high-speed operation. In such situations, a higher
design speed should be selected for all geometric features, particularly sight distance on crest
vertical curves and across the inside of horizontal curves....
People that want to keep the 80km/hr speed limit need to ask themselves what the purpose of a speed limit is. Answer is road safety. They need to then ask, how do they know how fast can one drive while still being safe. Answer is, engineering design or evaluation. Sadly, most don't make it to the second part. People that want the speed limit raised are just asking for an honest and fair evaluation. Having a road designed for 120km/hr and a speed limit of only 80km/hr and strictly enforcing the speed limit seems like a quick and easy way to basically tax the population further for no reason. I say no reason because someone driving at 90km/hr on a road designed for 120km/hr is still driving safely and yet being punished as though they are not.kamakazi wrote:Now actual speed limits can be set differently from design speed... that takes into consideration even more factors; but it is the place where the engineering starts and definitely isn't rubbish
Slartibartfast wrote:Exactly. Design speed of a highway has mostly to do with its geometry as outlined in AASHTO Policy on Geometric Design of Highways. If you get your hands on it and you are able to understand the geometric requirements you would see that the majority of our highways are either already designed for speeds above 80km/hr or can easily be upgraded to that it is. Some locations may need to have reduced speed limits of 80km/hr (I'm thinking like the bend by Gasparillo flyover)Nissan12 wrote:Slartibartfast wrote:Please tell me, exactly how do you "engineer" a road for a certain speed limit? Once you can answer that you will see why anybody that mentions that as a point against a higher speed limit is speaking utter rubbish. If you want to talk about safe highway speeds given the current wearing surface due to weathering, wear and tear and faulty construction then that is a different point and would only be applicable to specific locations of the highway inspected for such. Otherwise, please stop the spread of misinformation. It makes it worse for ussMASH wrote:i thought the roads aren't engineered to be safe above 80kmph?
could really remember a lot of words read about the engineering.
All physics (but hopefully some civil engineers here will chime in) horizontal curves and cross fall to counter centripetal and centrifugal forces, vertical curves for visibility and stopping distance based on speed.... Yeah, not just making a foundation and paving it...
Here is some info to further the discussions. Below are design criteria for freeways taken directly out of AASHTO - A POLICY on GEOMETRIC DESIGN of HIGHWAYS and STREETS 2001. I used the worst case scenarios where I could and kept it as simple as possible for ease of reference.
Consider the sight distance design criteria. You need to be able to see far ahead enough to notice dangers and stop in time. The values below take into account reaction time and stopping distance to give a total required sight distance.
According to AASHTO - A POLICY on GEOMETRIC DESIGN of HIGHWAYS and STREETS 2001 - Exhibit 3-1 and 3-2.
Sight distance for a car at 80km/hr is 130m
Sight distance for a car at 10km/hr is 185m
Sight distance for a truck at 90km/hr on a 9% downgrade is 187m (Makes sense for Heavy-T trucks to have a slightly lower speed limit)
For horizontal alignment taking into consideration the G forces on the car
According to AASHTO - A POLICY on GEOMETRIC DESIGN of HIGHWAYS and STREETS 2001 - Exhibit 3-14
Rounded Turning Radius for Vehicle traveling at 80km/hr with 4% superelevation (cross slope) = 280m
Rounded Turning Radius for Vehicle traveling at 100km/hr with 4% superelevation (cross slope) = 490m
I'll stop there for now but note that there is a lot more to the picture. Like how vertical curves affect sight distance. How grade and grade length affect truck speed and how truck speed affects traffic as well as how grade length affects truck braking.
All I want is for people to stop making uninformed statements like "Our highways nuh design for dat" to dismiss valid arguments. I'll leave you all with thisAASHTO - A POLICY on GEOMETRIC DESIGN of HIGHWAYS and STREETS 2001 wrote:SPEED
The speed of vehicles on a road or highway depends,
in addition to capabilities of the drivers and their vehicles, upon four general conditions: the
physical characteristics of the highway and the amount of roadside interference, the weather, the
presence of other vehicles, and the speed limitations (established either by law or by traffic
control devices)....
Design Speed
Design speed is a selected speed used to determine the various geometric design features of
the roadway. The assumed design speed should be a logical one with respect to the topography,
anticipated operating speed, the adjacent land use, and the functional classification of highway....
The selected design speed should be consistent with the speeds that drivers are likely to
expect on a given highway facility. Where a reason for limiting speed is obvious, drivers are more
apt to accept lower speed operation than where there is no apparent reason. A highway of higher
functional classification may justify a higher design speed than a lesser classified facility in
similar topography, particularly where the savings in vehicle operation and other operating costs
are sufficient to offset the increased costs of right-of-way and construction. A low design speed,
however, should not be selected where the topography is such that drivers are likely to travel at
high speeds. Drivers do not adjust their speeds to the importance of the highway, but to their
perception of the physical limitations of the highway and its traffic....
Where the physical features of the highway are the principal speed controls and where most
drivers choose to operate near the speed limit, a design speed of 120 km/h [75 mph] would serve
a very high percentage of drivers....
...On many freeways, particularly in suburban and rural areas, a design speed of 100 km/h
[60 mph] or higher can be provided with little additional cost above that required for a design speed of 80 km/h [50 mph]....
...Isolated features designed for higher speeds would not necessarily encourage drivers to
speed up, although a succession of such features might. In such cases, the entire section of
highway should be designed for a higher speed. A substantial length of tangent between sections
of curved alignment is also likely to encourage high-speed operation. In such situations, a higher
design speed should be selected for all geometric features, particularly sight distance on crest
vertical curves and across the inside of horizontal curves....
That's was perfected in Earth Mark 2crazybalhead wrote:DANNN!!!! You not supposed to be concentrating on the fiddly bits around fjords?
Nope. My point is that there's a whole lot of gum bumping with no information to back it up. I just want to hear what info they based this 80 km/hr speed limit on. Like JF.K saidkamakazi wrote:Aren't you forgetting in engineering there is something called "factor of safety"
They quoting "Engineering of the Roads" as a reason with absolutely no information. I want to see the reasoning behind their statements.JF.K wrote:I think the point sMASH was initially making is that the government and people in "power" were making statements that the "Engineering of the Roads" was the reasoning behind they not raising the 80km/hr speed limit.
Now all of a sudden they considering to raise it. It appears as though they were just BS people all the time (obviously).
And most likely the Syrians and their children getting pull over too much so a shot was called.
Slartibartfast wrote:That's was perfected in Earth Mark 2crazybalhead wrote:DANNN!!!! You not supposed to be concentrating on the fiddly bits around fjords?Nope. My point is that there's a whole lot of gum bumping with no information to back it up. I just want to hear what info they based this 80 km/hr speed limit on. Like JF.K saidkamakazi wrote:Aren't you forgetting in engineering there is something called "factor of safety"They quoting "Engineering of the Roads" as a reason with absolutely no information. I want to see the reasoning behind their statements.JF.K wrote:I think the point sMASH was initially making is that the government and people in "power" were making statements that the "Engineering of the Roads" was the reasoning behind they not raising the 80km/hr speed limit.
Now all of a sudden they considering to raise it. It appears as though they were just BS people all the time (obviously).
And most likely the Syrians and their children getting pull over too much so a shot was called.
De Dragon wrote:Slartibartfast wrote:That's was perfected in Earth Mark 2crazybalhead wrote:DANNN!!!! You not supposed to be concentrating on the fiddly bits around fjords?Nope. My point is that there's a whole lot of gum bumping with no information to back it up. I just want to hear what info they based this 80 km/hr speed limit on. Like JF.K saidkamakazi wrote:Aren't you forgetting in engineering there is something called "factor of safety"They quoting "Engineering of the Roads" as a reason with absolutely no information. I want to see the reasoning behind their statements.JF.K wrote:I think the point sMASH was initially making is that the government and people in "power" were making statements that the "Engineering of the Roads" was the reasoning behind they not raising the 80km/hr speed limit.
Now all of a sudden they considering to raise it. It appears as though they were just BS people all the time (obviously).
And most likely the Syrians and their children getting pull over too much so a shot was called.
You sir, are setting yourself up for a lot of disappointment The Gov't threw out a set of useless quotes and hoped that "engineering" in the BS answer would calm down their base. They didn't ,a nd usually do not, count on someone actually knowing that they are talking cacaholery and calling them out on it.
bluesclues wrote:Wah you mean better jap cars? U tryin to say a lexus better than a tiida? Boy rock so eh..
LOL
drchaos wrote:Nah meh boy Rohan say it will take some time! Changing laws takes more time than enforcing ones that already exist.
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