Should All Interstates be 6-laned?

[kphoger]

If you're going by here, the statement is:

If you are driving below 40 mph, you should leave at least one second for every 10 feet of vehicle length. For a typical tractor-trailer, this results in 4 seconds between you and the leading vehicle. For speeds over 40 mph, you should leave one additional second

I don't think though that this is an additional second per 10 feet of vehicle length, but one additional second overall. So, that would mean, for a 70 foot vehicle, not 14 seconds but rather 8 seconds of following distance.

Good interpretation.  If we use that (which sounds right to me), then the trucker will have made it 90% of the way to the slower vehicle's rear bumper by the time he gets to the one-minute mark.  Still ridiculous to expect him to have gotten back over already.

[CtrlAltDel]

If you're going by here, the statement is:

If you are driving below 40 mph, you should leave at least one second for every 10 feet of vehicle length. For a typical tractor-trailer, this results in 4 seconds between you and the leading vehicle. For speeds over 40 mph, you should leave one additional second

I don't think though that this is an additional second per 10 feet of vehicle length, but one additional second overall. So, that would mean, for a 70 foot vehicle, not 14 seconds but rather 8 seconds of following distance.

Good interpretation.  If we use that (which sounds right to me), then the trucker will have made it 90% of the way to the slower vehicle's rear bumper by the time he gets to the one-minute mark.  Still ridiculous to expect him to have gotten back over already.

Perhaps, but 8 seconds of following distance is still quite a bit, and I would wager, more than is commonly given. It would be like starting to pass here when the truck is under the bridge. That is 20 dashed lines ahead.

[kphoger]

Perhaps, but 8 seconds of following distance is still quite a bit, and I would wager, more than is commonly given.

I agree.  But can you really imagine such a law actually being passed, considering what's recommended?  And my scenario involves an 8mph speed differential.  Imagine a 4mph speed differential instead.

[kkt]

Do agencies really consider "sometimes people have to drop down to the speed limit" as a reason for widening a highway?

Of course not and I agree with the point you're making. But couldn't a similar question be asked for justification of  "limited access" highways in extreme remote rural areas?

I've driven on highways overseas in lightly populated areas that were 6-lanes,
so there had to be some justification for it beyond my personal example of being stuck behind slow vehicles.

It's hard to know why there's lightly populated 6-lane freeways.  Maybe they were built in anticipation of future growth that hasn't happened yet?  Maybe there is a seasonal traffic generator and you just haven't been there at that time?

There are certainly some 4-lane freeways out west where it would just be silly to add two lanes.

[CtrlAltDel]

Perhaps, but 8 seconds of following distance is still quite a bit, and I would wager, more than is commonly given.

I agree.  But can you really imagine such a law actually being passed, considering what's recommended?  And my scenario involves an 8mph speed differential.  Imagine a 4mph speed differential instead.

Fair enough. A law will definitely have to allow for people going by the book.

That said, I think it worth noting that the FMCSA just borrows its following distance information from the Virginia Department of Transportation, and the link posted to cite it is broken.

[Avalanchez71]

Where is the magic money going to originate from?  Six-lanes takes away the natural feel of the rural environment.

[vdeane]

Six-lanes takes away the natural feel of the rural environment.

This reminds me of someone...

[LilianaUwU]

I'd argue some Interstates don't need four lanes, let alone six. Just look at I-95 in northern Maine.

[Henry]

In the most populated areas, yes.

In the most remote ones, no.

[Scott5114]

Where is the magic money going to originate from?  Six-lanes takes away the natural feel of the rural environment.

So you're saying we can end rural poverty by expanding interstates to six lanes? /s

[pderocco]

The FMCSA recommends that, for speeds over 40 mph, a driver leave 2 seconds of following distance per 10 feet of vehicle length.  For a 70-foot tractor-trailer combination, that comes to 14 seconds of safe following distance.

If we assume that the slow-moving vehicle is going 60 mph and the trucker is going 68 mph, then here are the distances each vehicle will have traveled within one minute:

slower vehicle @ 60 mph = 88 ft/sec → 5280 feet (1 mile)
passing truck @ 68 mph = 100 ft/sec → 6000 feet (1 mile + 720 feet)

Your math is wrong. 60mph is indeed 88fps, and 68mph is very close to 100fps. But 14 seconds is 1232ft at 88fps, and 1400ft at 100fps.

The easier way to calculate this is based on speed difference, for which you're using 8mph as an example. That's 11.733fps. or about 6 seconds to go the length of a 70ft truck. I would say that when trucks are lined up, they leave about their own length between them, maybe a little more. For one truck to get from that position behind another truck to that position ahead of the other truck takes moving four truck lengths relative to the other truck, which would be 24 seconds. If they kept two truck lengths between them, they'd have to move six truck lengths, which would be about 36 seconds. If they left much more, those gaps would have cars in them. So I don't think a minute is an unreasonable limit.

If one truck can only go 2mph faster than another (which is, shall we say, insufficiently rare), then you're talking 2 to 3 minutes. That agrees with my experience. If that's the best they can do, they should just settle back and go 2mph slower than they want, or wait until there are no cars within a mile behind them, which happens occasionally enough in light traffic.

[ElishaGOtis]

It's hard to know why there's lightly populated 6-lane freeways.  Maybe they were built in anticipation of future growth that hasn't happened yet?  Maybe there is a seasonal traffic generator and you just haven't been there at that time?

The argument for widening I-10 to 6 lanes in the Florida panhandle is exactly this: future traffic demand. The other reason is hurricane evacuation--while there may not be significant traffic now, there will be if Pensacola & Navarre have to evacuate inland.

https://nwflroads.com/projects/413062-4

[DJStephens]

I've spent a lot of time on the road the past 12 months, coast to coast. A thought that crossed my mind: Should all interstates be 6-lanes? I can't count how many times I've been stuck behind two semi-trucks or slow moving cars side by side, which can even cause traffic in the most remote areas. Seems like an 3rd lane each way is needed...if anything for safety reasons. Apologies if this topic has been discussed before.

Am of belief there is another thread with this very same topic.  Although it might refer to "spot" widening of rural four lane segments.   Might to a good idea to merge.   Have mentioned the areas on I-10, near Benson, AZ and the need for prudent coherent addition of truck climbing lanes to the OUTSIDE in that area.   All too often, the cheap way out is pursued, in terms of median elimination, and shifting and skewing is introduced.   

[kphoger]

Your math is wrong.

Figures.  I knew someone would correct me.

It might be easier to prohibit trucks occupying all lanes in a row unless they can pass and pull over in less than a minute.

If one truck can only go 2mph faster than another ... then ... they should ... wait until there are no cars within a mile behind them ...

That would still be illegal under your proposed rule.

[michiganguy123]

If you're going by here, the statement is:

If you are driving below 40 mph, you should leave at least one second for every 10 feet of vehicle length. For a typical tractor-trailer, this results in 4 seconds between you and the leading vehicle. For speeds over 40 mph, you should leave one additional second

I don't think though that this is an additional second per 10 feet of vehicle length, but one additional second overall. So, that would mean, for a 70 foot vehicle, not 14 seconds but rather 8 seconds of following distance.

Good interpretation.  If we use that (which sounds right to me), then the trucker will have made it 90% of the way to the slower vehicle's rear bumper by the time he gets to the one-minute mark.  Still ridiculous to expect him to have gotten back over already.

Perhaps, but 8 seconds of following distance is still quite a bit, and I would wager, more than is commonly given. It would be like starting to pass here when the truck is under the bridge. That is 20 dashed lines ahead.

I guarantee a bunch of cars would be passing on the right

[kphoger]

FWIW, I find that the 2-second rule generally works out to around five skip lines or so.  So 20 skip lines doesn't sound all that unreasonable to me for a trucker.

[Plutonic Panda]

I sure wish most of them were. It seems like we're slowly moving in that direction anyways.

[pderocco]

Your math is wrong.

Figures.  I knew someone would correct me.

It might be easier to prohibit trucks occupying all lanes in a row unless they can pass and pull over in less than a minute.

If one truck can only go 2mph faster than another ... then ... they should ... wait until there are no cars within a mile behind them ...

That would still be illegal under your proposed rule.

I changed my proposal.

[JREwing78]

In a magical fantasy land where highway funding is limitless, I would rather see non-freeways be brought up to freeway standard rather than wasting widening on freeways that aren't heavily trafficked.

I can justify a widening if a lower-traffic road has significant weekend travel far above "normal" conditions that causes a safety concern. But there's an awful lot of Interstates that have such little traffic that, minus Federal mandates, would still be 2-lane highways today. They're already empty - they don't need any help!

It's not just about the construction costs - it also jacks up the maintenance costs (including snowplowing). In the northern Michigan hinterlands, for example, you'll frequently see MDOT keeping only one of the two travel lanes open during snowstorms.

[thisdj78]

I'd argue some Interstates don't need four lanes, let alone six. Just look at I-95 in northern Maine.

Is I-95 only two lanes in parts of Maine? Or do you mean conceptually it could be just 2 lanes? To that point, I always wonder why I-95 wasn't built towards Quebec City vs New Brunswick.

[kkt]

If money is really gonna be free, I'd just love for interstates to get repaved once in a while.  Hope that's not too wild to ask for!

[Big John]

I'd argue some Interstates don't need four lanes, let alone six. Just look at I-95 in northern Maine.

Is I-95 only two lanes in parts of Maine? Or do you mean conceptually it could be just 2 lanes?

That was originally the case before the other 2 lanes were eventually built.

[SilverMustang2011]

In a magical fantasy land where highway funding is limitless, I would rather see non-freeways be brought up to freeway standard rather than wasting widening on freeways that aren't heavily trafficked.

Alternatively, I'd like to see 2-lane US Highways or major State Roads be brought up to 4 lanes from 2. It may be overkill but there's nothing as frustrating as being stuck behind a slow car or truck on a 2-lane road in a no passing zone, with traffic from the opposite direction coming when you're in a passing zone. I would start with 2-lane sections on a road that's mainly 4 lanes (I.E. Florida State Road 60 between Indian Lake Estates and Yeehaw Junction)

[SEWIGuy]

In a magical fantasy land where highway funding is limitless, I would rather see non-freeways be brought up to freeway standard rather than wasting widening on freeways that aren't heavily trafficked.

Alternatively, I'd like to see 2-lane US Highways or major State Roads be brought up to 4 lanes from 2. It may be overkill but there's nothing as frustrating as being stuck behind a slow car or truck on a 2-lane road in a no passing zone, with traffic from the opposite direction coming when you're in a passing zone. I would start with 2-lane sections on a road that's mainly 4 lanes (I.E. Florida State Road 60 between Indian Lake Estates and Yeehaw Junction)

Highways shouldn't add lanes due to your frustrations.

[JREwing78]

In a magical fantasy land where highway funding is limitless, I would rather see non-freeways be brought up to freeway standard rather than wasting widening on freeways that aren't heavily trafficked.

Alternatively, I'd like to see 2-lane US Highways or major State Roads be brought up to 4 lanes from 2. It may be overkill but there's nothing as frustrating as being stuck behind a slow car or truck on a 2-lane road in a no passing zone, with traffic from the opposite direction coming when you're in a passing zone. I would start with 2-lane sections on a road that's mainly 4 lanes (I.E. Florida State Road 60 between Indian Lake Estates and Yeehaw Junction)

Highways shouldn't add lanes due to your frustrations.

Perhaps not, but it *does* indicate a need for some kind of relief measure. It's a lot safer if your roadway has passing lanes or other measures to break up long platoons of cars, as it decreases the perceived need to recklessly pass other drivers. There's a reason long 2-lane highway stretches like US-2 or M-28 in the U.P. of Michigan have numerous passing lane sections. Being stuck behind Grandpa Joe doing 45 mph in his clapped-out Winnebago for 20 miles until you finally have a break to pass is a special kind of hell.