speeding offences

[doug3030]

What is the optimum speed for the roads to transfer the maximum number of cars ?
It turns out that if everyone sticks between 70 and 80 this will result in the shortest average time on the road.

Are we talking about transferring the maximum number of cars or about an individual car reaching its destination in the shortest possible time?

Lets look at optimum speed to transfer the maximum number of cars first. Lets make a huge assumption that everyone is following the accepted guidelines of leaving 2 seconds travelling time between their vehicle and the one in front of them. to make the maths simple lets assume that the distance is measured from the centre of the car to avoid complicating the equation by the length of the vehicle.

Based on that assumption, it does not matter how fast they are going, the road will allow passage for the same number of cars per hour.
Taking it a stage further and allowing for the vehicles to have length, then obviously, the faster the vehicle goes, the less time it takes to travel its own length, so the faster they are travelling the more vehicles will be able to traverse a given length of road. One point for travelling faster.

Now for the shortest average time on the road: Its a no-brainer isn't it? The faster you can go the sooner you get there. We hear people say "It took a while to get here because the traffic was bad" have you ever heard someone say "It took a while to get here but the road was actually transferring the optimum number of cars". I have never heard anyone say that or even care about that. I do not know any traffic engineers or town planners.

If people are travelling in a 100km/hr zone and doing 70 or 80 instead of 100 surely it is because that stretch of road will not support that volume of traffic travelling at the posted speed limit. We get this on a daily basis in Melbourne, and I am sure in most other large/capital cities. Saying that you will get there faster by sitting on 80 instead of 100 is just government spin doctoring. The solution is to upgrade the roads, not to lie to the people. Not all of us are stupid.

Cheers

Doug

[FenceFurniture]

Not all of us are stupid.

Well ExKEEyuse me - speak for yourself.

[doug3030]

Well ExKEEyuse me - speak for yourself.

Well if you cannot identify with NOT being stupid its not my fault

(note excessive use of smilies. If I add many more the board will reject the post.)

Cheers

Doug

[ian]

I do not know any traffic engineers ...
Cheers

Doug

Hello Doug

Now you do

[doug3030]

Hello Doug

Now you do

Hi Ian, I certainly hope you are better than the one who does the work for our local council or you won't be getting any invites to my barbeques either

Cheers

Doug

[pmcgee]

I say employing some people to do *this* would be a reasonable use of speeding $$s

[doug3030]

I say employing some people to do *this* would be a reasonable use of speeding $$s

I do not have a motor cycle but I have actually done similar things to people who richly deserve it. If we can get some funding I would apply for the job.

Cheers

Doug

[FenceFurniture]

Hello Doug

Now you do

Ah, well just the man then Ian. Rather than keep going OT, perhaps you can help me here.

[BobL]

If people are travelling in a 100km/hr zone and doing 70 or 80 instead of 100 surely it is because that stretch of road will not support that volume of traffic travelling at the posted speed limit. We get this on a daily basis in Melbourne, and I am sure in most other large/capital cities. Saying that you will get there faster by sitting on 80 instead of 100 is just government spin doctoring. The solution is to upgrade the roads, not to lie to the people. Not all of us are stupid.

Yes it is about volume of traffic and we all experience that but it's more subtle than just the road not being big enough. In the US they tried to cope with congestion by just adding more lanes to the freeways and they found it did not help much. To get the traffic to travel at the speed limit during peak periods would require 10 -15 lanes which has its own problems not to mention the cost so there has to be a smarter way.

It is definitely not easy to explain but I'll give it a try. If you try to sit on 100 along with a substantial proportion of the other inconsiderate drivers who also insist (it's the goddam right after all) to sit on 100 the pack will indeed end up moving at 70. If everyone was to not do more than 80 then the average pack speed will indeed be more than 70. A single inconsiderate driver may indeed be able to average significantly more than this provided the other inconsiderate divers don't join that driver in attempting to travel at the speed limit. As soon as enough inconsiderate drivers start doing this the pack speed will drop as week as the individual drivers speed will also drop.

This has nothing to do with government spin doctors. Its a classic optimisation problem in mathematics. These mathematicians are paid big bucks to determine the optimum speed and sequence of all sorts of processes, computer programs, timetables, loading shipping containers, sequences of digging up ores, assembly of manufactured goods, traffic flow etc. They save businesses and governments billions of dollars a year. Modern society would collapse if these guys did not do their stuff. If you think this is peanuts and common sense just try reading the technical reports they put out - most of us are unlikely to even understand the paragraph let alone the text. Heres a link to a study of increasing average freeway on ramp speeds http://www.me.berkeley.edu/~horowitz...M_TRR_2011.pdf

Some of these problem was tackled many years ago. It's a failure of governments to implement their recommendations which has lead to greater congestion than necessary. Look at how long it took to automate traffic lights for major minor road intersections to give a time priority to the major road and that one was common sense.

The lower speed does indeed sound stupid but it has been demonstrated in places like Germany where they usually have unlimited speed limits on freeways. They installed variable speed limits on some sections of their autobahns near major cities and by imposing a speed limit of 130 or 80 or whatever they got more cars through per hour than they did when it was all open speed limit. If anything the spin doctoring centred around too high a traffic density making it too dangerous for open speed limits in the situations but the traffic engineers were more interested in getting more cars through.

Here is another one that has been studied in great detail. When two major freeways meet at higher traffic density, vehicle merging can be a nightmare. The degree of congestion is largely controlled by the drivers that insist on doing the speed limit. This leads to massive stop start driving and the inevitable Crawl. If the speed limits are dropped by 20 kph more cars get through in the least possible time. This is now commonly used in European freeway junctions.

[FenceFurniture]

Its a classic optimisation problem in mathematics.

And the ants have had it nailed for millions of years, god bless 'em.

I'm not going anywhere near that link of yours Bob - it'll fry my brain and I'm just off to beddiebyes.

[ian]

Here's something few people know about.

Lets say the speed limit on a freeway is 100 and the traffic density is high but not yet grid locked .

What is the optimum speed for the roads to transfer the maximum number of cars ?

about 60km/h, but the actual "optimum" speed varies depending on the lane width, the number and size of trucks, trailer and caravans in the traffic stream, the number of traffic lanes, the spacing of entry and exit ramps and the volume of traffic entering and exiting, the horizontal curvature, the vertical grade AND the experience of the drivers -- do nearly all of them drive the route at that time every day, or is the traffic situation new to them?

The lane switchers and tailgaters that insist on trying to do the speed limit in higher traffic densities only slow things down not just for everyone else but for them as well.

these people have the most negative impact when the traffic is still relatively "light" -- for peak hour conditions.

If I can find it, I'll post the plot we did a few years ago of the speed / volume data from a 80km/h road

[BobL]

about 60km/h, but the actual "optimum" speed varies depending on the lane width, the number and size of trucks, trailer and caravans in the traffic stream, the number of traffic lanes, the spacing of entry and exit ramps and the volume of traffic entering and exiting, the horizontal curvature, the vertical grade AND the experience of the drivers -- do nearly all of them drive the route at that time every day, or is the traffic situation new to them?

Yep it's complicated.

these people have the most negative impact when the traffic is still relatively "light" -- for peak hour conditions.

There ya go!

If I can find it, I'll post the plot we did a few years ago of the speed / volume data from a 80km/h road

Good

[Ari2]

Driving.... is that state of mind where everyone else is wrong...

[BobL]

Driving.... is that state of mind where everyone else is wrong...

Ever noticed how slow at reacting that driver is at the head of the queue when the light turns green?
Then the way the drivers behind dawdle and fail to keep up
They must be the main reason I'm always catching red lights!

[Dodgy Dovetails]

Of course, your car first has to actually make it onto the road!

https://www.youtube.com/watch?v=PGMUGjlV5HU