Slashdot Mirror
Domain: trb.org
Stories and comments across the archive that link to trb.org.
Comments · 27
-
European mass transit v US mass transit
This appears to be part of a general trend, transit costs in the US have been massively subject to "cost disease" https://en.wikipedia.org/wiki/Baumol's_cost_disease. However, the effect is much more pronounced for mass transit in the US than in Europe or elsewhere http://trrjournalonline.trb.org/doi/abs/10.3141/2541-01?journalCode=trr. While there are some arguments that how the US treats trains has advantages over Europe http://ti.org/antiplanner/?p=11847, the cost difference in new ones is gigantic. In this particular case, it is combining very badly with other issues, including the insanely high prices of land in California.
-
Re:Cost-benefit analysis
We've been doing that for decades.
How's that? Our licensing requirements are a joke. Not surprisingly, our highway fatality trends suck compared to other countries. What exactly have we been going for decades?
-
Re:More nation-wrecking idiocy
I think you'll need to try again after you get some more sleep, that link doesn't even mention a left turn lane, it seems like it's talking about a road called Suicide Lane because there were 88 accidents there in 11 months, but no evidence that there was a "suicide lane" there that caused 88 accidents.
Searching for "suicide lane" accident studies gets me articles like this one where apparently the "correct" thing to do is to never allow anyone to ever turn left again because some old woman turned left without checking for oncoming traffic. Likewise "Police and engineers often deride such lanes as 'suicide lanes,' not so much because cars might collide head-on, but because they allow people to cross traffic anywhere." I guess walling off left turns forever resolves my question of whether having the turning lane is safer than having people stop in the "fast" left lane to turn left, though if you're going to go to the expense of installing a wall on a 7 lane road, you might as well give up and upgrade it to a ramp-access freeway with service/frontage roads and underpasses to get to the other side.
The more professional terms "bidirectional left turn lane" or "two way left turn lane/TWLTL" gets a few actual studies. This study says that it's hard to determine if raised medians actually stop wrecks compared to TWLTL or if they move them to the cross streets where people are trying to go around the median to get to the other side. It suggests that raised medians are appropriate for residential sections (like your picture) rather than commercial sections, and feedback from people and companies on proposed median treatments seems to mirror that, with business developers preferring two way left turn lanes to raised medians, and residential developers and residents preferring wide, landscaped medians to both TWLTL and small concrete medians. This study from the '70s likewise suggests that TWLTL are recommended for commercial development. I did find this study where someone complained TWLTLs are scary, which amused me since apparently "scary" is a reason to erase all the lines from the road, but also a reason to not allow people to turn left.
If I had to go around a raised median every day I left my house, I too would demand it to be a very wide landscaped median, so I could actually U-turn around it without having to execute a 3 point turn (this study recommends to plan for a 48 foot turning radius for passenger cars, like turning from an 11' lane around a 22' median with two 11' lanes on the other side ). I'm afraid the street you've got in your photo is just irredeemably fucked. Add frequent speed humps and set the speed limit to 15 MPH with active enforcement by a local sheriff hired with neighborhood association dues to convince through traffic to find some other way around.
-
Re:What about a bus?
Fair enough. I was working from memory, couldn't remember where intercity busses fit in the mix and was too lazy to try to find it. I stand corrected. The TRBs TCRP 79 reports the average energy consumption for intercity buses as 713 BTU/(passenger mile). As such, the revised hierarchy ought to be:
- 1. Bicycles,
- 2. Walking,
- 3. Intercity passenger busses,
- 4. Planes,
- 5. Long-haul passenger trains,
- 6. et c.
-
Re:If "yes," then it's not self-driving
I have never seen a single study to show that 0.08% is "too strict". In fact, it is extremely lenient by most other country standards. A quick perusal showed this:
http://trid.trb.org/view.aspx?...It concluded impairment begins with any deviation, and almost all people are significantly impaired by 0.08% (lending credence to the idea that the line is too lenient, not too strict).
If you have a study that actually shows what you purport, I'm sure people would love to see it. -
Re:Study financed by
I posted something similar above. NCHRP Report 731 hews pretty closely to the recommendations in the ITE Traffic Engineer's handbook. I'll add that the MUTCD, section 4d.26 refers to that 3 second minimum as guidance, and uses "should," rather than "shall" or "will."
-
Re:Study financed by
Three seconds is the minimum duration as per federal law.
What gave you that impression? Signal timing is determined by an equation, but may have some minimum defined by local or state law, or in a design manual.
At 25 MPH with no grade, depending on law or policy, it may be perfectly permissible to have a 2.8s interval, though it's common in practice to round that to a minimum 3s. Here's the equation from the 1999 ITE handbook:
Y=t + 1.467v/2(a+32g), where
t=perception-reaction time, typically assumed to be 1 s,
v=speed in MPH (ITE recommends using the 85th percentile speed, but many agencies use the posted speed.),
a=deceleration rate, assumed to be 10 ft/sec^2,
g=grade.
If you want to read more, NCHRP report 731details recommended guidelines, and provides some history for the recommendations. -
Re:From a buffoon
Let's have a look at the numbers.
Having heard that road wear is proportional to the fifth power of axle weight, I thought I would see what wear proportion that works out as, given that there are presumably more cars than trucks, and the differing mileages of these types of vehicle. As I write this, I have not done the final calculation. I will use a couple of papers and some government statistics.
Looking at a couple of papers (The economic and environmental benefits of increasing maximum truck weight: the British experience, Alan C. McKinnon, 2005. The cost of relying on the wrong power—road wear and the importance of the fourth power rule (TP446), Richard Johnsson, 2004, Impacts of Increased Goods Vehicle Weight Limits - A European Case Study, Proceedings of Fourth International Symposium on Heavy Vehicle Weights and Dimensions, 1995, the exact proportion of axle weight to road wear varies depending on factors including road surface type, anywhere from 3rd or 4th power of axle weight, all the way up to the 9th power. I chose 4 as a lowish-average.
Taking a Heavy Goods Vehicle (HGV) weight of 15 tons and an average of 4 axles (HGV maximum weights: a brief guide gives a maximum for HGVs of 44 tons over 6 axles, and I don't have a good source, but the minimum to count as a HGV is 7.5 tons, presumably with 2 axles), this gives 3.75 tons/axle. For cars I assumed 1.5 tons and two axles; 0.75 tons per axle. The ratio of these figures is 5. 5^4 = 625 times as much road wear per axle.
Traffic statistics are in vehicle-kilometres, so to use these we need to multiply this back up by the number of axles per vehicle. 4 for trucks and 2 for cars gives 625*(4/2) = 1250 times as much road wear per vehicle per kilometre.
Keeping with the euro theme, I got transport statistics from the UK department for transport. 240 billion miles driven in the UK in 2011 by cars/taxis, heavy goods vehicles 16.4 billion. 240/16.4 = 14.63 times as many miles driven by cars, compared to heavy goods vehicles (I have deliberately left out 'vans', or other vehicles that carry smaller loads than the HGVs that my axle weights are for). So now we have 1250 times as much road wear per vehicle for HGVs, divided by 14.63 as the ratio of cars-HGVs, gives 85.4 times as much road wear by HGVs. Take the reciprocal and subtract from 1 to get that as a proportion, 0.988, or 98.9%.
Wow, I really didn't expect to get so close to the GP's guess. My estimate for axle weight for HGVs I think is low if anything; I could easily have gone for 20 tons over 4 axles, which would have given 99.6%. I have also assumed that HGV weight is evenly spread over the axles; it strikes me that the rear axles will carry more weight, and so since the road wear varies with the 4th power of this, the real figure is probably higher. -
Re:No, if you are doing it during traffic hours.
Q. Isn't slower always safer? A. No, federal and state studies have consistently shown that the drivers most likely to get into accidents in traffic are those traveling significantly below the average speed.
-
Cross comment from redditNot my comment. From here:
As a Traffic Engineer I work with this issue frequently. Their are numerous benefits of roundabouts that outweigh the risks, so much so that numerous states, including New York, require the analysis of a roundabout at any new intersection.
The first issue is safety, roundabouts reduce what we call, Conflict Points, between pedestrians, bicycles and vehicles. The middle island also provides pedestrian refuge for a two stage crossing. Roundabouts also force cars to slower speeds which improves safety and reduces the risk of an automobile collision.
As far as delay and driver in vehicle perception, roundabouts statistically have a lower average delay than all-way-stop-controlled (AWSC) intersections for streets that have a volume of less than 20,000 vehicles per day. The Level of Service (LOS), is a measure of driver perception of service at an intersection. The average LOS for an AWSC at peak hours is F (Delay of 172 s), while a roundabout provides LOS C (Delay of 21 s). Both LOS determinations are for the best approach. So as you can see, the benefits are clear.
The downside is that many people are unfamiliar with them, a learning curve and the unwillingness to try out something new, as the adage goes, "If it ain't broke, don't fix it". Here is an example, I met with a consulting firm that performed a study in Buffalo, NY to put in a roundabout. The measurements worked and LOS would have increased for the approaches. However after installation the city council decided to put stop-signs at the roundabout approaches, against the recomendation of the traffic engineers. This was a foolish move on the part of the City as a major benefit to roundabouts is the Yield approach. Their is still no change to date.
It is an uphill battle but once people become more familiar you will see them throughout the US.
If you would like more information on roundabouts their are two resources from the federal government:
1. Roundabouts: An Informational Guide
2. NCHRP (National Cooperative Highway Research Program) Report572
-
Straw mattressing also deployed
Joanna Lumley on Graham Norton:
Now we are sending two machines out at the request of BP to spread this mattressing along the coast and not only does it help clean the water, it gives the wildlife something to step on to.
2010-07-21
BP's secret weapon in the great oil mop-up? Joanna Lumley and a giant straw mattress -
From the No Duh Dept.
Good grief. From TFA:
The surveys demonstrated that land use type, roadway type, and building setbacks all played significant roles in determining vehicle speeds. Most importantly, though, having cars parked along the side of streets accounted by itself for a reduction in travel speeds
And:
So the conclusion is this: People can be induced to reduce their driving speeds when cars are parked along the roadways, when buildings are close to the street, and when those buildings include commercial rather than residential activity.
Who would have thought that by reducing a driver's visibility, the driver would go slower to give themselves time to react to surprises? You? You in the back? Are you some kind of smartass? The Connecticut Department of Transportation studied this for four years. There's no way you could have arrived at the same conclusion so quickly!
This study was useful in determining how much people slowed down -- quantifying it at about 10% -- but sweeping on to claims like, "reducing the rates of passenger fatalities and generally encouraging a safer urban environment" is silly. Streets packed with parked cars, pedestrians, nearby buildings, et. al. are generally more dangerous precisely because clear lines-of-sight are cut off. Sane drivers know this, reduce their speed, and then -- making wild hand-waving guesses, here -- wind up with about the same overall level of "dangerousness" as when driving on uncluttered roadways.
-
Re:Will these kill more people?
And I suppose your comments are from the "I like to use rhetoric instead of facts" department. Seriously, here's a recent report on the topic:
http://www.trb.org/Main/Public/Blurbs/On_a_Crash_Course_the_Dangers_and_Health_Costs_of_161951.aspx
-
Re:suddenoutbreakofcommonsense
I think you have no business driving, when you clearly fail to understand that 1) it's imposible to keep withing exactly 1 MPH of the limit and 2) that most spediometers are not even accurate to that level and 3) the measuring device at the wheel isn't accurate enough to properly determine speed.
Even tire ware affects accuracy considerably: http://en.wikipedia.org/wiki/Speedometer#Error
It has nothing to do with not being able to controlyour car; it has to do with not being able to control your car precisely enough to always be at the legal limit.
And lets be real here; speed limits aren't about safety, they are about revenue generation:
http://en.wikipedia.org/wiki/Speed_limit#85th_percentile_rule
http://trb.org/publications/nchrp/nchrp_rpt_504.pdf -
Re:28 MPH is not fast enough for realistic street.
No, speed limits are set to generate revenue.. otherwise they wouldn't be set lower than they should.
-
Re:Shouldn't matter...1) Speed limits without any "good" reason are rare. I would agree that some are probably only to raise money, but I think they are the exception. Actually, you'd be surprised how many speed limits are too low. A group of residents wanted radar enforcement of the 35mph limits on the major roads in my city, but state law requires municipalities to have a traffic engineering study to justify any limits before they can be enforced with radar (anti speed trap law). The engineering study found that 90% of them were posted far too low. Most major streets were found safe at 45 or 50 MPH. So did they change the posted limits? No, they left them at 35 and chose not to use radar. Personally, I think most speed limits are not low enough and they do sacrifice some innocent lives for convenience. See, the problem with speed limits is that they are set by ignoramuses like you who think "slower is safer, always", rather than by experienced traffic engineers who understand the dynamics of traffic flow. An unreasonably low limit that results in a mix of driving speeds across a wide range, from the slow "I drive the posted limit, always" folks to the "I drive what the road can handle" ones, is more dangerous because of the wide differential than a higher limit that gets people moving closer to the same speed.
The canonical example is the federally mandated 55mph speed limit put in force in the early 70's. It was initially instituted as a fuel saving measure, but dogmatic "safety nazis" pointed to a correlated reduction in accidents and it became "common wisdom" that a lower limit is safer. When the federal 55 limit was eased in 88 and repealed in the 90's, there were all kinds of dire predictions of increased mayhem on the highways. In reality, accidents went down! The problem is that elected officials and bureaucrats don't actually understand the 85th percentile rule. The safest limit is one where 85% of drivers naturally obey the limit. The 55 limit saw compliance rates under 20%! Studies (see pg 88) show that nearly all posted limits are 8 to 12 mph below the 85th percentile.
So what about the reduction in accidents in 1974? Well, it's a classic case of "correlation is not necessarily causation". The late 1960's saw a dramatic improvement in the safety of automobiles. Everything from increased use of radial instead of bias ply tires to mandatory seat belts came into play in the late 60's. The biggest improvement, however, was the 1968 mandate of front wheel disc brakes. If you've never driven a car with 4 wheel drum brakes, it's easy to miss the importance of this. So starting in '68 you have all new cars being equipped with disc brakes. The "replacement point" on cars of that vintage was around 5 years, meaning that the majority of driving miles were logged in cars 5 or fewer years old. Older cars were still driven, but were largely relegated to secondary status (e.g. wife's car, kid's car, etc). So around 1973 the tide turns from drum brakes to disc brakes... and accidents went down. It was pure chance that the 55 limit coincided with that. Really, the 55 limit was more dangerous, but the increase in vehicle safety hid that. Sadly, we still have morons like you who blindly belive the mythology. Perhaps that can be changed by people like me handing out education and insults, but I'm not optimistic. Injuring yourself will have a cost for society. This is an utterly invalid reason for laws curtailing behavior in a free society. Free individuals do not "owe" society anything. Society is a voluntary association. Fucking safety nazi shitheads like you would do well to understand that. -
Re:Video Evidence
developing nation highways
20 mph difference increases accident risk 3X
Hmmm... Not the same thing, but a link showing that Montana was safer without speedlimits on highways. -
Re:Social hack - use "bullfight" for "speed trap".Do you really expect someone to go out to each road, and try and determine the fastest allowable speed? It is a lot easier (cheaper) just to say, every one of these roads has X for a speed limit. Oddly enough, they don't seem to mind putting in the effort to *police* speed limits.
If we assume that each road will have a speed trap on it at least once, then they've *already got* the data to determine an appropriate speed limit as per the 85th percentile rule. Interestingly, as Wikipedia notes, "a review of available speed studies demonstrates that the posted speed limit is almost always set well below the 85th-percentile speed by as much as 8 to 12 mph (see p.88)." This indicates that in a vast majority of cases, speed limits are set according to political rather than safety concerns. -
Re:Sorry, couldn't resist ...When will more Americans die from terrorism in any given year than die on America's highways? I believe we will see that occur in our lifetime.
Terrorist Incidents > by Region Range: 01/01/1968 - 04/14/2007
North America Incidents:588 Injuries:4344 Fatalities:3568
Middle East / Persian Gulf Incidents:13788 Injuries:52063 Fatalities:25859
Global TOTAL Incidents:32904 Injuries:114327 Fatalities:49379http://www.tkb.org/IncidentRegionModule.jsp
The U.S. Department of Transportation's National Highway Traffic Safety Administration (NHTSA) has released preliminary projections on motor vehicle traffic crash fatalities and injuries during 2005. According to a preliminary report, 43,200 died on the nation's highways in 2005, up from 42,636 in 2004. Injuries dropped from 2.79 million in 2004 to 2.68 million in 2005, a decline of 4.1 percent.
http://www.trb.org/news/blurb_detail.asp?id=6195
What the hell are you talking about? If you'll look above global terrorism in the past 39 years, barely passes the number of deaths caused by cars in 2005 in the US alone. There are better sources for information than wikipedia. You're wrong, you're just wrong.
-
Did you even read your source?
Did you even read your source? YOUR source said that there were 88 less deaths per year in the entire US. That is 88 people out of 300,000,000. When someone says that you have a 1 in a million chance, they are talking about this. That 1 in a million is even including those who are severely ill with other things, the elderly, those with compromised immune systems, and whatnot. The reason there was a 92% drop in childhood deaths is because a child dying of chicken pox is so rare that 1 less death shows up as a huge percentage. Using percentages with such low numbers is the "desperate" argument. Here are some death numbers to ponder before claiming that the chicken pox vaccine is even worthy of notice:
Estimated deaths due to no chicken pox vaccine: 88
Deaths due to lightning strike: 82
Alzheimer's: 60,000
Assault: 17,500
Driving: 40,000
Flying: 200
High School Football: 30
Traveling to and from school: 800
The numbers of possible lives saved by this vaccine is so low as to be under the radar. You could get almost half as good results by just banning high school football. Heck, you could get just as good results by having 10% of the current school kids moving to home schooling. Using risk of death by chicken pox as an excuse for the vaccine is simply FUD, so that the parents who don't want to take a week off work can feel good about their decision. It is also entirely possible that the numbers of deaths due to chicken pox has actually been increased dramatically, but pushed off for 20 years. Ask your pediatrician. They will tell you that the vaccine might not last into adulthood, and we all know how much worse that will be.
So, if you are really interested in reducing the risk of death for your child, you would take your kid to a pox party, and start home schooling immediately. Heck, just not letting your kid play football is better protection than the chick pox vaccine. -
Re:20 miles from work?
Is this actually true? I would like to ask Mr. Lutz for a cite or three to back this assertion.
It seems reasonable at first blush, after all, unless you just LOVE sitting in your car idling down the freeway for hours a day, you probably want to live somewhere close to work. The average distance from home to work in Los Angeles is 8.2 miles (pdf), which includes claims that this is "consistent" with census data (except that it looks like the Census doesn't report distance, they report travel time) and compares with other metropolitan areas. This (another pdf) says that the average first job for people going off welfare is 6.5 miles away. This PDF claims that work causes people to drive an average of 12 miles per day. This site says that over 1/3 of workers in the 100 largest cities drive more than 10 miles to work. -
Actually, Americans tolerate 15 9-11's per annum
Around 45,000 transportation-related deaths take place in the US every year. That's 15 times the number of premature deaths that occurred on 9-11. Every year.
http://trb.org/news/blurb_detail.asp?id=5380
The point is that if we were truly concerned about our lives, we would pay attention to this problem with as much vigor and zeal as we pay attention to terrorism - or American Idol. But this kind of fact doesn't get any play in the media. It is roundly ignored.
Just because the deaths are dispersed doesn't mean the cost or the tragedy is any less. Put those 45,000 bodies in a pile together with all the twisted metal and accident debris, and you have a pretty nasty mess.
And there are at least 6 times as many injuries as there are deaths. Transportation-related injuries raise healthcare costs for everyone, over a long span. Such things are not fixed in part because the systems are too entrenched. And tragedy is profitable to many. Insurance, pharma, etc. "A stitch in time saves nine," sure. But just think of how much you can charge for those nine stitches!
But they are also not fixed because of the diffuse nature of the events. There is a lack of public awareness to these surprising statistics. And due to our cultural conditioning it is anathema to openly compare lifestyle-related self-destruction to obliquely-motivated wanton destruction. Because the themes are too emotional for our rational minds to engage them.
Yet the fact is that beneath the themes that color these events, the dynamics are simple. Directed energy spells consequences. American progress, the lifestyle of travel, coupled with imperfect systems, leads us to a certain amount of collective self-destruction, which we accept as the cost of our manner of being. Meanwhile, energy is being directed from without to harm and punish us collectively. Outwardly destructive and wanton, our foreign policy has been and remains: to instill instability in regions we wish to usurp, and to engage openly only with those who are sufficiently subservient to capitalist interests. We step on many toes, and we get bitten by radicals, sometimes even the very radicals we armed and trained in the first place.
Fact is, even with so many deaths every year, from major causes (like transportation-related incidents and heart disease and obesity), and minor causes (like electrocutions and terrorism), we're still increasing in numbers and thriving generally. The herd is healthy enough, so if a few are culled it's acceptable to the bottom line - the bottom line of those who are paying attention to such numbers. Those who know and could do something, aren't, in any case. So draw your own conclusions. -
Re:Source?
-
Re:Of Course, Bridges Are Easy[snip]there are always well-known requirements prior to completing the design. These requirements do not change after completion.
Um, not quite.
There are lots of other examples (this or this for instance)
-
Uncoated polycarbonate? Who made that blunder?Now that was dumb. Polycarbonates are strong, but not hard. The eyeglass lens industry solved this problem years ago. Even the bus window industry has solved this problem. Optical polycarbonate surfaces are routinely hard-coated, and an anti-glare coating is often added at the same time.
The cool solution, which Apple probably now has to use to get their reputation back, is sapphire. That's what scratch-resistant high-end watches use. Put an 0.15mm sapphire layer on top of the polycarbonate, and you can dump the thing in with your keys without worrying. It's not that expensive for a phone or music player sized screen. Some of Nokia's high-end phones have a sapphire screen.
Of course, doing it right might cut into those 40% profit margins at Apple.
-
Re:a.k.a. Personal Rapid Transit (PRT)I've been involved with evaluating PRT systems using simulation for about 10 years now. I am always surprised that it is considered new and exciting, but the stuff you do every day rarely seems exciting, right?
The Morgantown WV system has been cited here several times. At the time, it was called a PRT system, but now most insiders think of it as a GRT ("Group Rapid Transit") system. Think of a PRT as a taxi that takes you and your friends from place to place, and you can see that a GRT (which hauls 10-30 people) is not quite as personal. Thus, we call it GRT to distinguish it.
Someone here mentioned the Denver baggage system, and they are right that PRT operates very similarly. The difference is that the cars can rear-end each other because they hold things, not people. When you carry people, you have lifesafety issues to contend with which makes it far more difficult to achieve PRT's promise.
Here's a couple weaknesses, because people always seem to emphasize the positives:- The "brick wall" test. In short, for proper lifesafety you need to ensure that the vehicles don't follow each other too closely. To do that, you make sure that there is space between you and the vehicle you are following, such that if it instantaneously stops (hits a brick wall) you can come to a safe stop without hitting the vehicle. The faster you go, the larger the gap. Generally speaking, we use a 5 second "headway" between vehicles like we were taught in driver's ed.
Significantly, vehicle designers claim that there will never be a brick wall stop, and so they claim they only have to decelerate as fast the vehicle in front of them. Imagine this as tailgating. Also imagine the car in front of you hits the brakes, so you hit yours a little harder, and the driver behind you stands on his brakes, and pretty soon you have that "shock wave" that everyone experiences on the freeway in rush hour. In practical terms, insurance companies will not allow such a system and governing bodies won't either. For now, the brick wall test is the standard.
And, the brick wall test eats up a lot of capacity: designers claim 1/2 second headways instead of 5 second headways. That's a big difference. - Merging logic. Where two tracks come together, there is a big conflict that must be managed safely. Turns out, this merging is something we as humans can do pretty well on the highway, but train control systems have a hard time doing it. Its not that it is impossible, but it is hard to make it optimal. Because capacity is such an issue with PRT systems, getting close to optimal is important.
- Empty Vehicle Management. When you arrive at a station, you want a vehicle to be waiting for you. That's pretty easy if there are the same number of people who arrive at the station from somewhere else as those who want to depart the station. But what if the station has more people leaving than arriving? Pretty soon, you are out of empties. Likewise, some other station has an excess of empty vehicles. You can send them from one station to another, but this eats up the capacity of the guideway. This management of empties is perhaps the hardest thing to overcome, and it the solution is specific to each system. What works in Gotenberg Sweden will not work in Houston, TX. Empty vehicle management was a huge issue for the Denver baggage system.
If you are really interested in PRT, come to the Transportation Research Board (http://trb.org/) annual meeting in DC in January. There is going to be several presentations on the state of the practise in PRT at the meeting.
PRT has a lot promise, but unfortunately there have been too many broken promises and its credibility is tarnished. A pity, really. - The "brick wall" test. In short, for proper lifesafety you need to ensure that the vehicles don't follow each other too closely. To do that, you make sure that there is space between you and the vehicle you are following, such that if it instantaneously stops (hits a brick wall) you can come to a safe stop without hitting the vehicle. The faster you go, the larger the gap. Generally speaking, we use a 5 second "headway" between vehicles like we were taught in driver's ed.
-
Re:Meanwhile, in the city...
(IAAUP - I am an Urban Planner, or at least I played one at University)
Per dwelling unit, per acre, or per person, any way you decide to calculate it, it is more expensive for people to live in the suburbs than in the city. The costs of living in the suburbs are usually offloaded onto the local, state, and federal government (think interstates, costs of sprawl, etc). The downside of this situation is that these governments pay for the increased costs by allowing the construction of strip malls and "big box" stores which cause more congestion and sprawl.
The closer that people live together, costs per person or dwelling unit go down significantly.
For more information on this phenomena, refer to Transportation Research Board's final report on the cost of sprawl:
http://gulliver.trb.org/publications/tcrp/tcrp_rpt _74-a.pdf