States Should Consider Modest Increases in Speed Limits

[J N Winkler]

why was 85% established as a magic number?  it seems to me to be limiting in the case of areas where culturally, people seem to enjoy driving slowly.

The way I understand it, it has to do with the U shape of the distribution of accident incidence by speed.  The general rule of thumb, at least in the 1950's (when I think the 85th percentile doctrine was first articulated--I believe Ralph Nader's Unsafe at any Speed has a capsule account of how it was developed), was that the low point of the accident curve is at the 85th percentile speed, with the rate increasing sharply at 15 MPH over and 15 MPH below.  I suspect the origin of the 85th percentile doctrine is ultimately a paper by David Solomon published in a 1950's issue of Proceedings of the Highway Research Board, but I cannot check this easily since the university library nearest me seems to have dumped its back numbers of PHRB.

A road would have to have a very low traffic volume indeed in order for it not to be possible to determine the 85th percentile speed to reasonable statistical certainty within a relatively short period of time.  In situations where the road is not built yet or not open to traffic, the design speed (usually cited on the title sheet of the construction plans) is usually a reasonable estimate of the 85th percentile speed.

In the case of Oregon, systematic underposting of the freeways leads to a skewed distribution of speeds since a high proportion of traffic chooses to comply with the speed limit just to avoid hassling with law enforcement.  So on a typical freeway in Oregon you get one peak of traffic speeds around 70 MPH (most rural freeways in Oregon are designed for 70 and were so posted before the NMSL was introduced), and a second peak at the posted limit.  I don't see much "cultural" fondness for low limits in Oregon--merely a desire to avoid criminal liability.  If the speed limits were raised to correspond to the underlying design speeds, the traffic distribution would almost certainly normalize.  Crash severity is not necessarily a similar story and I think this is the real basis for Kitzhaber's opposition to higher speed limits.

[corco]

nowhere in the US do I know of consistent lane courtesy. not even the 75mph states.  Arizona comes to mind for having terrible lane courtesy, as does Florida (okay that's a 70mph state, but still).  just what kind of idiot-ball has someone swallowed to decide that doing 58 in the left lane is a reasonable way to go through life?

Nebraska comes to mind as being really good. South Dakota and Wyoming are too, but there isn't really enough traffic anywhere to really test it.

I was driving back from Phoenix a couple weeks ago and an Arizona Highway Patrol was cruising at 68 in a 75 in the left lane- on the six lane stretch between Casa Grande and Tucson! People were passing him on the right and everything. I couldn't even believe it.

[agentsteel53]

I was driving back from Phoenix a couple weeks ago and an Arizona Highway Patrol was cruising at 68 in a 75 in the left lane- on the six lane stretch between Casa Grande and Tucson! People were passing him on the right and everything. I couldn't even believe it.

that's the other problem... police cars going slowly in traffic cause major congestion because people slow down by some irrational amount. 

cops should always be doing a good fast speed if they need to get anywhere (say, 3-4 miles per hour faster than the speed of traffic, and certainly a good 8-10 over the speed limit), as opposed to becoming rolling roadblocks. 

[agentsteel53]

A road would have to have a very low traffic volume indeed in order for it not to be possible to determine the 85th percentile speed to reasonable statistical certainty within a relatively short period of time.

agreed, but let's say that a road has such little traffic that an individual driver is hardly ever interacting with another ... in that case, the concept of "85th percentile" goes out the window, because local to that driver there isn't nearly enough traffic to be able to make that distinction.

I think that if, statistically speaking, I am the "only car on the road" (namely, no one within a quarter-mile of me or so, to have to consciously pay attention to), I should be able to set my speed of safe operation based on terrain, road quality, weather, and wildlife considerations.  

[hbelkins]

just what kind of idiot-ball has someone swallowed to decide that doing 58 in the left lane is a reasonable way to go through life?

Having your residence in Ohio seems to be a frequent cause of this affliction.

[bugo]

Arkansas drivers take Speed Limits as "suggestions". Interstates are 70, Expressways are 60-65. Yet I often feel like I'm the only one who obeys these speed limits.

Then come to Oklahoma.  Most of the traffic drives below the speed limit, and rarely do you ever see anybody going over 100, even on the turnpikes.  The last time I was in Little Rock, I got blown off the road several times by cars going 100 or more.

[kphoger]

I was driving back from Phoenix a couple weeks ago and an Arizona Highway Patrol was cruising at 68 in a 75 in the left lane- on the six lane stretch between Casa Grande and Tucson! People were passing him on the right and everything. I couldn't even believe it.

that's the other problem... police cars going slowly in traffic cause major congestion because people slow down by some irrational amount.  

cops should always be doing a good fast speed if they need to get anywhere (say, 3-4 miles per hour faster than the speed of traffic, and certainly a good 8-10 over the speed limit), as opposed to becoming rolling roadblocks.  

Ooh, this bothers me too.  I was once heading west out of Tulsa on 412; the speed limit was, I forget exactly, let's say 70 mph.  A patrol car was going 71 in the left lane, I started to come up alongside him at 72, he revved his engine and pointed at his radar gun, I slowed to match his speed exactly for the next mile or two, then he swerved right in front of me from the left lane to exit on the right.  Yeah, let me tell you, I sure respected him.....  Then I got pulled over closer to I-35 for going 7 over the limit with absolutely no traffic around.......  I hate that turnpike.

I have thought for quite a while now that they should do away with simple speeding tickets.  If someone is speeding but not posing a threat to the safety of the other drivers around him, then he doesn't deserve a ticket.  If he is speeding AND is posing a threat to the safety of the other drivers around him, then he should get a reckless driving ticket–which should not have the option of being changed to a non-moving violation as is a speeding ticket in many places.

[corco]

I have thought for quite a while now that they should do away with simple speeding tickets.  If someone is speeding but not posing a threat to the safety of the other drivers around him, then he doesn't deserve a ticket.  If he is speeding AND is posing a threat to the safety of the other drivers around him, then he should get a reckless driving ticket–which should not have the option of being changed to a non-moving violation as is a speeding ticket in many places.

I agree- for instance, I can't believe that it's more legal to drive alongside another car at 69 MPH in a 70 zone on a non-packed freeway than it is to quickly and safely pass the 69 MPH vehicle at 80 MPH in a 70 zone. Unless you're in the middle of the city, it's just dangerous to drive alongside somebody else- what if there is a refrigerator in the middle of the road over the next little hill, or a deer comes running out? I want all the roadway I can use to maneuver around it. If you're right next to me driving the same speed, I don't have that.

There's just no way it's not safer to pass other vehicles quickly and decisively than it is to play the cruise control game and pass somebody at .05 MPH faster because your cruise is at 75 and the guy next to you is at 74.95. Especially when one of the vehicles involved is a truck.

[agentsteel53]

I can't believe that it's more legal to drive alongside another car at 69 MPH in a 70 zone on a non-packed freeway than it is to quickly and safely pass the 69 MPH vehicle at 80 MPH in a 70 zone.

such behavior is dangerous, and incredibly stupid ... yet I see drivers do that all the time.  the worst is when they are coming up fast behind me, and then decide to slow down and park themselves just diagonally beside me.

to paraphrase Chief Wiggum - "what is your fascination with my forbidden blind spot of mystery??"

[J N Winkler]

There's just no way it's not safer to pass other vehicles quickly and decisively than it is to play the cruise control game and pass somebody at .05 MPH faster because your cruise is at 75 and the guy next to you is at 74.95. Especially when one of the vehicles involved is a truck.

I agree, but the die-hard believers in absolute speed limits would retort that it is always your option to slow down so the other guy can finish his overtaking maneuver.

[1995hoo]

I wouldn't say that's a cultural norm here.  It's more a product of our a**hole safety-Nazi governor (about whom people are starting to whisper the word "recall") and the speed differentials and lack of lane courtesy that results from his refusal to even consider raising the limits to something reasonable.

nowhere in the US do I know of consistent lane courtesy. not even the 75mph states.  Arizona comes to mind for having terrible lane courtesy, as does Florida (okay that's a 70mph state, but still).  just what kind of idiot-ball has someone swallowed to decide that doing 58 in the left lane is a reasonable way to go through life?

I've long found that Virginia residents are among the worst in terms of absence of lane discipline. I was driving on the Trans-Canada Highway near Mont-Tremblant once, nobody else on the road except for one car up ahead that happened to be in the left lane....sure enough, a Virginia plate. I know some people would say "why does it matter if nobody else is on the road," but I've always followed the rule of staying out of the passing lane unless you're passing, period, except in the situation where the road conditions are such that the passing lane is the only one in reasonable shape (Autoroute 15 between the US border and Montreal used to be a classic example of that). I'm finding on the Virginia part of the Beltway that it's more and more common to see someone cruise along in the left lane, then suddenly bomb across anywhere from four to six lanes in one swoop to exit at the last second. I'll never understand that either.

I've also long found, however, that Maryland drivers are among the worst in terms of having an irrational deep-seated fear of driving in the right lane. They might not automatically default to the left lane if there are more than two, but on many of my trips along I-95 in Maryland I've found that I can actually go fastest if I get in the right lane, simply because everyone else will be in the other two or three lanes to the left and I can just step on it and dust them all. It makes no sense to me at all and I have to surmise that they're afraid that at some point they might have to slow down because of someone getting on the highway.

I suppose this is more an issue for a road sign related thread, but I've always disliked the signs that say "Slower Traffic Keep Right" and I've wished they'd be replaced with "Keep Right Except to Pass." "Slower Traffic Keep Right" is a sign that some people read as giving them some level of discretion in that they think they don't have to keep right if they're not "slower," and they think that going the speed limit means you can drive in any lane. The majority of drivers probably do not consider themselves "slower drivers." "Keep Right Except to Pass" is unambiguous. Of course, it's also meaningless if it's not enforced, but that's a whole different discussion.



To answer the original query, I've never really liked the idea of "default speed limits" except perhaps in extremely small states like Rhode Island. I think that just as the National Speed Limit was a bad idea because it failed to recognize the valid differences in conditions around the country, a "default speed limit" within a state of any significant size does precisely the same thing. I don't like the idea of presuming that any non-Interstate cannot have a higher limit than any Interstate, either, because I don't think the assumption that an Interstate is automatically a better road is valid.

[agentsteel53]

I agree, but the die-hard believers in absolute speed limits would retort that it is always your option to slow down so the other guy can finish his overtaking maneuver.

I don't think I've ever seen that happen.  

a related problem is when I attempt a suicide pass on a two-lane road, and the driver being passed speeds up.  that's just pure unadulterated dick on a plastic tray.  

I once had a guy, doing maybe 63 in a 65, race me up to 105, then when I decided to give up as there was someone coming ... he slowed down as well.  I managed to out-guess his intentions just once and got behind him before I got splattered.

I'm not really sure what point he was trying to prove, but it may have been the most ludicrously stupid mile I've ever driven in my life.

[Takumi]

I've long found that Virginia residents are among the worst in terms of absence of lane discipline. I was driving on the Trans-Canada Highway near Mont-Tremblant once, nobody else on the road except for one car up ahead that happened to be in the left lane....sure enough, a Virginia plate. I know some people would say "why does it matter if nobody else is on the road," but I've always followed the rule of staying out of the passing lane unless you're passing, period, except in the situation where the road conditions are such that the passing lane is the only one in reasonable shape (Autoroute 15 between the US border and Montreal used to be a classic example of that). I'm finding on the Virginia part of the Beltway that it's more and more common to see someone cruise along in the left lane, then suddenly bomb across anywhere from four to six lanes in one swoop to exit at the last second. I'll never understand that either.

I've also long found, however, that Maryland drivers are among the worst in terms of having an irrational deep-seated fear of driving in the right lane. They might not automatically default to the left lane if there are more than two, but on many of my trips along I-95 in Maryland I've found that I can actually go fastest if I get in the right lane, simply because everyone else will be in the other two or three lanes to the left and I can just step on it and dust them all. It makes no sense to me at all and I have to surmise that they're afraid that at some point they might have to slow down because of someone getting on the highway.

I suppose this is more an issue for a road sign related thread, but I've always disliked the signs that say "Slower Traffic Keep Right" and I've wished they'd be replaced with "Keep Right Except to Pass." "Slower Traffic Keep Right" is a sign that some people read as giving them some level of discretion in that they think they don't have to keep right if they're not "slower," and they think that going the speed limit means you can drive in any lane. The majority of drivers probably do not consider themselves "slower drivers." "Keep Right Except to Pass" is unambiguous. Of course, it's also meaningless if it's not enforced, but that's a whole different discussion.



To answer the original query, I've never really liked the idea of "default speed limits" except perhaps in extremely small states like Rhode Island. I think that just as the National Speed Limit was a bad idea because it failed to recognize the valid differences in conditions around the country, a "default speed limit" within a state of any significant size does precisely the same thing. I don't like the idea of presuming that any non-Interstate cannot have a higher limit than any Interstate, either, because I don't think the assumption that an Interstate is automatically a better road is valid.

I have to agree, I constantly get passed by people on the right when I'm in the center lane on I-95 (I have to stay in the center lane to get to work, else I wind up on I-85. I'm not doing it to be a jerk.) and it's always by locals. The left lane is rarely if ever used for passing here. Of course, even if the police actually enforced it, I'm sure it'd still happen.

[Takumi]

a related problem is when I attempt a suicide pass on a two-lane road, and the driver being passed speeds up.

That's happened to me multiple times. Not to 105, mind you, but I've gone to pass someone on a two lane road with traffic coming and they speed up. It's even worse whe a blind curve is coming up after the passing zone.

[Duke87]

I tend to stay in the left lane on the freeway but I'm going fast enough that I'm passing all the cars to the right of me and it's easier to just stay in the left lane than to get in and out of it as needed to pass.

Of course, if I come across someone going slower than desired in the left lane, I will gladly pass them on the right given the chance - although it isn't always their fault (speed limit 65, they're going 75, I'm trying to go 85...).

In my experience, though, if I come up behind someone in the left lane fast enough they usually are smart enough to move over and get out of my way when they get a good chance to.

[agentsteel53]

if I come up behind someone in the left lane fast enough they usually are smart enough to move over and get out of my way when they get a good chance to.

send some of these people my way.

I will move over even if I have a bad chance to do so - if the speed limit is 70, and there's a truck doing 68 and I'm passing him doing 77... if someone behind me is doing 83, I will happily speed up to 83 to accommodate him.  if he's doing 95, I will happily speed up to 83 to accommodate him.  anything past that I'm thinking "screw, I'm 13 over the limit, I might be cooked"

if speed limit enforcement weren't so silly in its rigor, I'd happily speed up to 95 to accommodate him.

now, if that truck is doing 68, and someone pulls out in front of me and insists on doing 69 ... well, he's an assclown.

[corco]

Quote from: corco on Today at 02:44:49 PM
There's just no way it's not safer to pass other vehicles quickly and decisively than it is to play the cruise control game and pass somebody at .05 MPH faster because your cruise is at 75 and the guy next to you is at 74.95. Especially when one of the vehicles involved is a truck.

I agree, but the die-hard believers in absolute speed limits would retort that it is always your option to slow down so the other guy can finish his overtaking maneuver.

And somebody who believes in both could re-retort that if you have to exceed the speed limit to safely pass, and a ridiculously slow pass is not a safe pass, then you should not be passing at all. Exactly as happens on a two lane road.

I will move over even if I have a bad chance to do so - if the speed limit is 70, and there's a truck doing 68 and I'm passing him doing 77... if someone behind me is doing 83, I will happily speed up to 83 to accommodate him.  if he's doing 95, I will happily speed up to 83 to accommodate him.  anything past that I'm thinking "screw, I'm 13 over the limit, I might be cooked"

I pretty much do this too.

[hobsini2]

I wouldn't say that's a cultural norm here.  It's more a product of our a**hole safety-Nazi governor (about whom people are starting to whisper the word "recall") and the speed differentials and lack of lane courtesy that results from his refusal to even consider raising the limits to something reasonable.

nowhere in the US do I know of consistent lane courtesy. not even the 75mph states.  Arizona comes to mind for having terrible lane courtesy, as does Florida (okay that's a 70mph state, but still).  just what kind of idiot-ball has someone swallowed to decide that doing 58 in the left lane is a reasonable way to go through life?

Actually, I would say from personal experience, Lane Courtesy is alive and well in rural parts of Texas, Kansas, Nebraska, and Wyoming.  Now this may have something to do with me have some "storm chasing" equipment on the vehicle in spring but that's how i see it.

[J N Winkler]

I agree, but the die-hard believers in absolute speed limits would retort that it is always your option to slow down so the other guy can finish his overtaking maneuver.

I don't think I've ever seen that happen.

I have done it on occasion.  Frankly, given the choice, I prefer to speed up (even unto the point of mild illegality) rather than slow down (going 55 on a freeway designed for 70 is like sex in a raincoat), but if I have no better option but to slow down, I will do it.

And somebody who believes in both could re-retort that if you have to exceed the speed limit to safely pass, and a ridiculously slow pass is not a safe pass, then you should not be passing at all. Exactly as happens on a two lane road.

Yup!  But, see, it is the other guy's bad decision to overtake on a low speed differential:  the question is what you then decide to do about it.  For every instance of bad behavior on the road there is someone to behave badly and someone else to suffer from it.  Often the most expedient solution is to remove yourself from the situation so that you are not the one suffering.

I will move over even if I have a bad chance to do so - if the speed limit is 70, and there's a truck doing 68 and I'm passing him doing 77... if someone behind me is doing 83, I will happily speed up to 83 to accommodate him.  if he's doing 95, I will happily speed up to 83 to accommodate him.  anything past that I'm thinking "screw, I'm 13 over the limit, I might be cooked"

I pretty much do this too.

I try to do the same, since that is usually less trouble than aborting my own overtaking maneuver so the other driver can go ahead.  There are tradeoffs though.  The kind of person who storms up behind you doing 95 in a 70 is not usually the kind who is disposed to wait behind you in the passing lane while you develop an adequate following distance between yourself and the car you have just passed before you change lanes.  Instead, he or she usually slaloms angrily around you.  I find it annoying, but if I were in the vehicle being overtaken I would be equally annoyed if someone cut back right in front of me immediately after passing me.  Given the choice between annoying someone through passivity and annoying someone else through action, I take the former.

[corco]

Instead, he or she usually slaloms angrily around you.  I find it annoying, but if I were in the vehicle being overtaken I would be equally annoyed if someone cut back right in front of me immediately after passing me.  Given the choice between annoying someone through passivity and annoying someone else through action, I take the former.

That makes sense. When that happens and I suspect a vehicle is going to slalom before I can safely merge in front of the car I just passed, I usually throw my right blinker on as soon as there is room  to move over, and then don't move over until it's actually safe to do so. The obvious downside of that is that it could scare the car in the right lane, but I've never had anybody slalom around me when I do it. I'm unsure as to whether that's worth the trade-off.  

Edit: In fact, when I write it out, I tend to dislike that practice. If it does indeed scare the car being passed, then the wrong car is being penalized- the guy in the right lane being passed is doing nothing "wrong" and shouldn't be in a position where they think they might have to brake. The burden is on me and the car behind me to sort the situation out, not the car being passed.  I suppose it has to do with traffic levels- if I were the car being passed in the middle of nowhere, I'd be a bit nervous about it, but in a city I wouldn't think anything of it. Then again, the gap distance is usually less in cities- I give a lot less room to cars I pass when I'm going 75 in the city than 75 in the middle of nowhere, simply because giant gaps are harder to find- in the middle of nowhere there's absolutely no reason not to leave a big gap.

I suppose that's something that irks me on rural freeways- the driving dynamic is very different between rural and urban, and folks whose behavior would be fairly unnoticed in an urban setting sticks out as unnecessarily reckless in a rural setting. Drivers who fail  to distinguish between the two settings are the annoying ones- although somebody driving like they're in the middle of nowhere when in a city won't stick out as dangerous, but they'll have a lot of trouble finding gaps wide enough to merge and probably be intimidated by changing lanes, or they'll insist on maintaining large gaps and brake incessantly, which does stick out as dangerous.

[agentsteel53]

they'll insist on maintaining large gaps and brake incessantly, which does stick out as dangerous.

I tend to maintain a large gap in following distance.  People, alas, think the space is for them.  no, you dumbass, the space is for me.

I do my best to tap the brakes as infrequently as possible.  If simply letting off the accelerator does the job, then I go with that.

[corco]

I tend to maintain a large gap in following distance.  People, alas, think the space is for them.  no, you dumbass, the space is for me.

I do my best to tap the brakes as infrequently as possible.  If simply letting off the accelerator does the job, then I go with that.

I naively try to balance the gap so that I'm a bit closer than I may ideally want to be but not so close that I think another car will try to sneak in. Alas, other cars still manage to sneak in. Tailgating is something that has come to annoy me a great deal more since I moved to Tucson then it used to- I think it's because it seems worse here than in other places (possibly because virtually all commuters are on surface streets for the duration of their commutes, unlike every other city of this size, which clogs the surface streets- driving in rushhour you get guys 5 feet behind you at 40 MPH because they're racing to beat the yellow light, and God help you if you have to brake- pretty much everybody I know who has lived here for a while has been rear ended. I'm still waiting for mine.).

Leaving a big gap is good if you're using that gap so that you can let your foot off the accelerator (thereby temporarily shrinking the gap), but if you insist on maintaining a gap of that size and hit your brakes just to maintain the gap, that's annoying. I don't see too many cars doing the latter, but the ones that do are really obvious.

[1995hoo]

I tend to maintain a large gap in following distance.  People, alas, think the space is for them.  no, you dumbass, the space is for me.

I do my best to tap the brakes as infrequently as possible.  If simply letting off the accelerator does the job, then I go with that.

I naively try to balance the gap so that I'm a bit closer than I may ideally want to be but not so close that I think another car will try to sneak in. Alas, other cars still manage to sneak in. Tailgating is something that has come to annoy me a great deal more since I moved to Tucson then it used to- I think it's because it seems worse here than in other places (possibly because virtually all commuters are on surface streets for the duration of their commutes, unlike every other city of this size, which clogs the surface streets- driving in rushhour you get guys 5 feet behind you at 40 MPH because they're racing to beat the yellow light, and God help you if you have to brake- pretty much everybody I know who has lived here for a while has been rear ended. I'm still waiting for mine.).

Leaving a big gap is good if you're using that gap so that you can let your foot off the accelerator (thereby temporarily shrinking the gap), but if you insist on maintaining a gap of that size and hit your brakes just to maintain the gap, that's annoying. I don't see too many cars doing the latter, but the ones that do are really obvious.

This is a huge problem around here and it's coupled with what seems to me to be a culture of "it doesn't count as a lane change unless I get in front of you." You can be the last car at the end of a line of 20 cars in the right lane, nobody behind you, coming up on an exit, and some guy coming up from behind you in one of the other lanes will pass you and then try to shove his way into or across the line at the exit point instead of just slowing down a bit and moving in at the end. They're desperate to cut over in FRONT of as many cars as possible rather than slowing down even a smidgen. So as a result a lot of people shove up close on the bumper in front of them.

I subscribe to two car magazines and they occasionally talk about cars that have the radar-based cruise control, like newer Jaguars. I've never driven a car that has that feature, but I imagine that on the East Coast it would border on useless because I'm sure it must be programmed to maintain a "proper" following distance, and as you say, if you do that, other drivers will think you're a pussy and will cut in front of you. I assume the radar-based cruise control would then just slow you down to restore the proper distance and then the same thing would happen all over again.

[J N Winkler]

That makes sense. When that happens and I suspect a vehicle is going to slalom before I can safely merge in front of the car I just passed, I usually throw my right blinker on as soon as there is room  to move over, and then don't move over until it's actually safe to do so. The obvious downside of that is that it could scare the car in the right lane, but I've never had anybody slalom around me when I do it. I'm unsure as to whether that's worth the trade-off. 

Edit: In fact, when I write it out, I tend to dislike that practice. If it does indeed scare the car being passed, then the wrong car is being penalized- the guy in the right lane being passed is doing nothing "wrong" and shouldn't be in a position where they think they might have to brake. The burden is on me and the car behind me to sort the situation out, not the car being passed.

I don't think there is one uniform answer that works in all situations of this kind.  I tend to improvise based on the speed differential between the vehicle I am passing and myself and the distance between myself and the car following me in the passing lane.  If the speed differential is large and the following car is not tailgating, I will consider moving over before I have developed an adequate following distance and then keep moving at passing speed until I have developed that distance, and then take my foot off the throttle and let cruise control pick up.  If the following car is riding my bumper, I will expect it to slalom and generally won't take special action to prevent it.  Then, once the following car has finished its slalom maneuver and is clear, I will develop following distance and move over normally.

Your trick with the turn signal is something I might try if I read the traffic ahead and judged that the slalom driver would be committing himself to two tight lane changes in order to get around me.  My philosophy in these cases is to clear the way for the assholes so that if and when they eventually wipe out, they will be far enough ahead of me that I will have ample time to react.

My personal rule on freeways in clear weather is to try to hold my speed when overtaking to under the speed limit plus 10 MPH.  I find this is usually ample for passing even vehicles cruising no more than a few MPH under the speed limit.  However, it can cause difficulty if my overtaking maneuver tells the vehicle being overtaken that he or she is moving too slow and needs to speed up.  In situations like this I make a decision as to whether he or she is trying to pace me and if I decide that he or she is, I back off sharply and pull in behind him or her, because I am not interested in exposing myself through sustained cruising above the speed limit.

I suppose it has to do with traffic levels- if I were the car being passed in the middle of nowhere, I'd be a bit nervous about it, but in a city I wouldn't think anything of it. Then again, the gap distance is usually less in cities- I give a lot less room to cars I pass when I'm going 75 in the city than 75 in the middle of nowhere, simply because giant gaps are harder to find- in the middle of nowhere there's absolutely no reason not to leave a big gap.

I have observed similar effects in cities.  In comparison to rural freeways, speed limits are generally significantly lower (in Kansas, 55 to 65 versus 75), level of service is typically much lower, and there are much greater volumes of traffic both entering and exiting, so the process of adjusting lane position and following distance is continuous, and drivers are much more willing to forgive well-calculated and well-signalled moves into narrow gaps in traffic.  I tend to place more emphasis on keeping my flank open than on cruising at a set speed because I want to be able to move over as necessary to let merging traffic in.  (Basic rule of driving, per AAA's Sportsmanlike Driving textbook which was a staple of driver education classes in the 1980's:  "Always leave yourself an out.")

In comparison, I think tight-headway slalom maneuvers on rural freeways with 75 limits and LOS allowing easy maintenance of 4-second following distance for dozens of miles have to be regarded as aggressive behavior.

[kphoger]

Off-topic (OR:  On the new topic)...

If there's someone on my tail, I don't bother leaving adequate following distance before moving over to the right; as mentioned, the distance only gets greater with every passing yard, and I don't want the guy behind me to hot-dog it in between us.  Sometimes I speed up a few ticks to minimize the faster guy's wait time (I sure appreciate it when others do the same for me), and sometimes I slow down and wait my turn (if I haven't yet gone into the left lane).  Sometimes, when I'm passing a string of cars, I'll even duck into the right lane, let the guy by, and then slide over behind him once he's passed me.

In México, there's a turn signal system that works fairly well.  Say I'm passing a string of slow-moving trucks.  A guy comes flying up behind me and wants to pass.  Typically, he has his left blinker on at this point to let me know he wants to pass.  I judge the situation and decide it's safer to finish passing the whole string of trucks before moving over.  To let him know this, I put on my left blinker, which means 'I see you, I'm still passing these guys, and I'll move over when I'm done'.  Once I'm side-by-side with the last truck, I swith to the right blinker, which means 'I'm getting over as soon as I'm clear'.  Usually, the guy backs off a little bit, and doesn't try and blow by me on the right.

Back on topic...

In theory, I don't like the idea of blanket or default speed limits either.  In theory, I think every stretch of road should have a study done to determine a safe speed limit.  But wouldn't that take a lot of man-hours (read: money) to complete nationwide?