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Old August 3rd, 2010, 04:34 PM   #1
Jevpls
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Road capacity calculations

I'm doing some road capacity calculations and now I'm stuck on road quality.
Does quality of pavement has a great impact on capacity?

Theoretically it does. For example, drivers can drive easily on good roads but they have to think before any actions on roads with potholes. Sometimes overtaking can't be done because of holes and it reduces the capacity of road.

Maybe there are values that could be used in this case, for example:

Good road pavement= max. possible capacity;
Average road pavement= max. possible capacity x 0.9;
Bad road pavement= max. possible capacity x 0.8


Probably HCM (Highway Capacity Manual) has some information but I haven't got it...

Any ideas?
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Old August 3rd, 2010, 04:47 PM   #2
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Porous asphalt has superior drainage features. In times of rain, this significantly increases capacity (or better; prevents that capacity decreases) as you don't need to have longer/safer following distances.
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Old August 3rd, 2010, 05:31 PM   #3
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How much is porous asphalt more expensive than regular asphalt per m²?
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Old August 3rd, 2010, 06:14 PM   #4
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According to the Dutch Road Authority, porous asphalt is about 20% more expensive to construct and 70% more expensive over it's entire life-cycle than dense asphalt.

The main reason for porous asphalt in the Netherlands is noise though. 2-layer porous asphalt can reduce as much as 6 dB compared to dense asphalt.
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Old August 3rd, 2010, 06:43 PM   #5
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But if we talk about usual asphalt?
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Old September 2nd, 2010, 09:32 AM   #6
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Any ideas?
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Old March 17th, 2011, 05:23 PM   #7
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About road capacity again.

As far as I know, theoretically capacity of a 2+2 road can be really high. Not only because of 4 driving lanes, but usually such roads have less single level intersections, have better curves (horizontal and vertical) and so on...
But what about real values? For example 2+2 road with 3,75 m wide lanes and 2 emergency lanes (~2,5 m). Could it have capacity like 80 000 vehicles per day?
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Old March 17th, 2011, 05:52 PM   #8
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only if there are no traffic lights. The busiest 2+2 roads I know with traffic lights handle up to 40.000 - 50.000 vehicles per day. If there is free flow, it could be double that, in fact the Dutch Coen Tunnel (A10 Amsterdam) has 2x2 lanes and carries 110.000 vehicles per day.
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Old March 17th, 2011, 06:08 PM   #9
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If you really want to calculate road capacity, you need hourly volumes per direction. For example, up to 1500 vehicles per hour per lane is free flowing. It can go up to 2200 - 2500 vehicles per hour per lane (even 3000 has been recorded), but then there are very big chances for congestion. It also depends on the amount of truck traffic, that why they invented the "car-equivalent" value. A truck is usually 2 - 3 car equivalents.
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Old March 17th, 2011, 07:50 PM   #10
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I don't have traffic lights in my situation.

I used old Russian methodology for my calculation and it recommends 2000-2200 per hour per lane as maximum value. It means that I'm not using too high values if you say that 2500 is normal (or even 3000).
Quote:
Originally Posted by ChrisZwolle View Post
It also depends on the amount of truck traffic, that why they invented the "car-equivalent" value. A truck is usually 2 - 3 car equivalents.
Don't worry, I didn't forget about trucks and buses

By the way, maybe do you know how great is max. capacity difference between 2+2 road with emergency lines and 2+2 road with only narrow shoulder? We have different types of 2+2 here in Latvia, but we none of them is full...AADT is too low.
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Old March 17th, 2011, 09:01 PM   #11
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I don't think the lack of shoulders indicate a significant capacity difference. However, roads with shoulders are more robust as no lane closures are needed in case of breakdowns.
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Old March 17th, 2011, 09:31 PM   #12
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Quote:
Originally Posted by ChrisZwolle View Post
The busiest 2+2 roads I know with traffic lights handle up to 40.000 - 50.000 vehicles per day.
A 2+2 road with traffic lights and no green wave in NW Ljubljana used to have 60,000 AADT before a motorway bypass was built.
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Old March 17th, 2011, 10:19 PM   #13
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Highway Capacity Manual
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Old March 17th, 2011, 11:24 PM   #14
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blogen,
HCM tells me how to calculate but I don't need it. I wanted not manual but information about real roads. Like I said - I calculated that capacity is ~80 000 vehicles per day. Is it real or not?

If you got any examples (like ChrisZwolle did) - I'll appreciate them.
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Old March 18th, 2011, 12:12 AM   #15
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80.000 vehicles on a 2x2 motorway(-like) road is fully loaded to capacity. More is possible, but not desired. Many countries widen 2x2 motorways to 2x3 lanes between 60.000 and 90.000 vehicles per day.
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Old March 18th, 2011, 12:42 AM   #16
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Quote:
Originally Posted by Jevpls View Post
blogen,
HCM tells me how to calculate but I don't need it. I wanted not manual but information about real roads. Like I said - I calculated that capacity is ~80 000 vehicles per day. Is it real or not?

If you got any examples (like ChrisZwolle did) - I'll appreciate them.
Use this link

http://infocar.dgt.es/etraffic/Busca..._buscar=Buscar

The "i" icone (info sensores)
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Old March 18th, 2011, 12:43 AM   #17
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Quote:
Originally Posted by ChrisZwolle View Post
80.000 vehicles on a 2x2 motorway(-like) road is fully loaded to capacity. More is possible, but not desired. Many countries widen 2x2 motorways to 2x3 lanes between 60.000 and 90.000 vehicles per day.
SANRAL reported it decided to upgrade the R300 between the N1 and N2 from 2x2 freeway to 2x3 when it reached in excess of 70 000 vehicles per day.

They also consider that grade-seperation and dual carriageway should be introduced when traffic volumes exceed 10-15 000 vehicles per day on national roads.
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Old March 18th, 2011, 09:10 AM   #18
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Quote:
Originally Posted by ChrisZwolle View Post
80.000 vehicles on a 2x2 motorway(-like) road is fully loaded to capacity. More is possible, but not desired.
Sure, it's obvious that 2+2 road with 14000 cars works better than the same road with 70000 or 80000 cars But if it's possible then fine! I had to calculate max. possible capacity.

Thanks, guys for help.
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Old March 18th, 2011, 11:18 AM   #19
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The question is that congestions can severely reduce the capacity of a road after a certain point. With safety distances preserved, the maximum flow capacity is attained at - usually - 90-95 km/h traffic. Of course people tailgate in back-up traffic at lower speeds, but when traffic falls below something like 60-70 km/h, the extra time taken by cars to drive through 2 points (meaning they are "eating up" lane capacity) doesn't compensate for reduced distance between cars, thus reducing overall practical capacity. When that happens, improvements can be made with access ramp controls to avoid degrading speed even more.
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Old March 19th, 2011, 02:19 AM   #20
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Quote:
Originally Posted by ChrisZwolle View Post
I don't think the lack of shoulders indicate a significant capacity difference. However, roads with shoulders are more robust as no lane closures are needed in case of breakdowns.
I don't know about Europe, but here roads without shoulders are not allowed have speed limits in excess of 80km/h.
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