How many lanes should a freeway have for LOS A B or C?

[tolbs17]

In my opinion,

4 lanes - 0 - 40,000

4 or 6 lanes - 40,000 - 50,000

6 lanes - 50,000 - 75,000

6 or 8 lanes - 75,000 - 85,000

8 lanes - 85,000 - 110,000

8 or 10 lanes or have express lanes - 110,000 - 125,000

10 lanes - 125,000+

[mrsman]

I'm sure one of the engineers on the board can actually tell us the answer.  This is not an opinion, there is actual science involved with understaning how many lanes are necessary to achieve a certain LOS, given certain AADTs (amount of annual traffic flow over a section). 

[hotdogPi]

I'm sure one of the engineers on the board can actually tell us the answer.  This is not an opinion, there is actual science involved with understaning how many lanes are necessary to achieve a certain LOS, given certain AADTs (amount of annual traffic flow over a section).

While I don't know the exact numbers, it must vary a bit based on daily schedules. Higher AADTs are possible for a given number of lanes if traffic is more evenly spread throughout the day (and night) with no huge spikes during rush hour.

[webny99]

I'm sure one of the engineers on the board can actually tell us the answer.  This is not an opinion, there is actual science involved with understaning how many lanes are necessary to achieve a certain LOS, given certain AADTs (amount of annual traffic flow over a section).

While I don't know the exact numbers, it must vary a bit based on daily schedules. Higher AADTs are possible for a given number of lanes if traffic is more evenly spread throughout the day (and night) with no huge spikes during rush hour.

On the other hand, roads with volume more evenly spread throughout the day likely have seasonal fluctuations to consider instead. On interstates like the Thruway and I-81, the peak should be regarded as a time of year ("weekends and holidays in the summer") rather than a time of day.

[sprjus4]

I'm sure one of the engineers on the board can actually tell us the answer.  This is not an opinion, there is actual science involved with understaning how many lanes are necessary to achieve a certain LOS, given certain AADTs (amount of annual traffic flow over a section).

It's not just AADTs, there's many other factors that go into it.

[MikieTimT]

I'm sure one of the engineers on the board can actually tell us the answer.  This is not an opinion, there is actual science involved with understaning how many lanes are necessary to achieve a certain LOS, given certain AADTs (amount of annual traffic flow over a section).

It's not just AADTs, there's many other factors that go into it.

One of those factors is the % of trucks that make up that AADT.  I'm sure everyone here who has done any driving cross-country whatsoever can attest to the agony of rolling roadblock after rolling roadblock of governed semis passing each other on 4-lane stretches between metropolitan areas that add lanes and options for getting around them.

[tolbs17]

I asked this question because sometimes US64/US264 gets congested when AADT is at 90,000 when looking at this (west of I-540).

http://ncdot.maps.arcgis.com/home/webmap/viewer.html?webmap=b7a26d6d8abd419f8c27f58a607b25a1

That's probably why they want to widen it from 6 to 8 lanes and add express lanes.

Also it's probably not the best to always believe that, you got people driving with their phones and them talking to people and that's what makes traffic slow and congested. Or if there's an accident.

I-95 in Northern Virginia is around 200,000 AADT which means it would need 10 lanes (or even 12) and 4-6 managed lanes to handle that much traffic.

___________________________________________________________________________________________________

Question - Does this thread belong in Traffic Control or General Highway Talk? I didn't know where to put it when i was thinking it should go under "General Highway Talk" or "Traffic Control". This thread basically has nothing to do with signs or signals.

[roadfro]

Level of Service is really a measure of delay. Number of lanes is only one input in the equation. AADT is not as important in the LOS calculation compared to other measures such as hourly flows and the saturation flow rate.

LOS fluctuates with time of day as well. You can have an intersection approach that operates at LOS D in the morning, LOS C midday, LOS E during the PM peak, and LOS A at 11pm... All of that can be dependent upon traffic volumes, turning movements, signal phasing, etc.

[johndoe]

Good answers so far.  Technically freeway LOS is a density (not delay) measure, but the two are certainly related ...you can find the curves if you want to dork out on Google

-We're more interested in peak hourly than daily volumes.
-A crucial variable is interchange spacing.  Technically the LOS methodology is too simplistic, so simulation tools are used to predict densities/speeds/delays.  Spacing and lane arrangement (option lanes, left exits, CD systems, weaving patterns) cause bottlenecks.
-In the big picture, some argue aiming for a certain LOS (or speed, or throughput, etc) isn't practical from financial p.o.v.  Most DOT don't have enough money to widen everything that hits LOS F.  You could also argue that these widenings are a temporary fix that may not have desired result (see induced demand) and just result in more pavement to maintain in the future for the poor DOT.  Ultimately widening jobs are usually up to the top decision makers and politicians (not strictly an engineering decision).

You may enjoy this slideshow on the topic for more detail:
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ce.memphis.edu/3161/pdf%2520files/Basic%2520Freeway%2520Segments_full.pdf&ved=2ahUKEwjKi_GAhZLmAhUSaq0KHTdzA9kQFjAPegQIBhAC&usg=AOvVaw2hyTfwcs2JV4EfrME7FbYM&cshid=1575120589227

[mrsman]

Good answers so far.  Technically freeway LOS is a density (not delay) measure, but the two are certainly related ...you can find the curves if you want to dork out on Google

-We're more interested in peak hourly than daily volumes.
-A crucial variable is interchange spacing.  Technically the LOS methodology is too simplistic, so simulation tools are used to predict densities/speeds/delays.  Spacing and lane arrangement (option lanes, left exits, CD systems, weaving patterns) cause bottlenecks.
-In the big picture, some argue aiming for a certain LOS (or speed, or throughput, etc) isn't practical from financial p.o.v.  Most DOT don't have enough money to widen everything that hits LOS F.  You could also argue that these widenings are a temporary fix that may not have desired result (see induced demand) and just result in more pavement to maintain in the future for the poor DOT.  Ultimately widening jobs are usually up to the top decision makers and politicians (not strictly an engineering decision).

You may enjoy this slideshow on the topic for more detail:
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ce.memphis.edu/3161/pdf%2520files/Basic%2520Freeway%2520Segments_full.pdf&ved=2ahUKEwjKi_GAhZLmAhUSaq0KHTdzA9kQFjAPegQIBhAC&usg=AOvVaw2hyTfwcs2JV4EfrME7FbYM&cshid=1575120589227

Thanks, the slideshow was really helpful.