Tachycardia refers to a heart rate that’s too fast. How that’s defined may depend on your age and physical condition. Generally speaking, for adults, a heart rate of more than 100 beats per minute (BPM) is considered too fast.
A profile for atrial or SVT
In general, those most likely to have atrial or supraventricular tachycardia are:
Children (SVT is the most common type of arrhythmia in kids)
Women, to a greater degree than men
Anxious young people
People who are physically fatigued
People who drink large amounts of coffee (or caffeinated substances)
People who drink alcohol heavily
People who smoke heavily
Atrial or SVT is less commonly associated with heart attack or serious mitral valve disease.
Episodes of faster-than-normal heart rate characterize
paroxysmal supraventricular tachycardia (PSVT). PSVT is a fairly common type of
abnormal heart rate. It can occur at any age and in people who don’t have other
heart conditions.
The heart’s sinus node typically sends electrical signals to
tell the heart muscle when to contract. In PSVT, an abnormal electrical pathway
causes the heart to beat faster than normal. Episodes of rapid heart rate can
last from a few minutes to several hours. A person with PSVT can have a heart
rate as high as 250 beats per minute (bpm). A normal rate is between 60 and 100
bpm.
PSVT can cause uncomfortable symptoms, but it’s not usually
life-threatening. Most people don’t need long-term treatment for PSVT. There
are medications and procedures that may be necessary in some cases, especially
where PSVT interferes with heart function.
The term “paroxysmal” means that it only happens from time
to time.
What are the risk factors for paroxysmal supraventricular
tachycardia?
PSVT affects about 1 in every 2,500 children. It is the most
frequent abnormal heart rhythm in newborns and infants. Wolff-Parkinson-White
syndrome (WPW) is the most common type of PSVT in children and infants.
PSVT is more common in adults under age 65. Adults over age
65 are more likely to have atrial fibrillation (AFib).
In a normal heart, the sinus node directs electrical signals
through a specific pathway. This regulates the frequency of your heartbeats. An
extra pathway, often present in supraventricular tachycardia, can lead to the
abnormally fast heartbeat of PSVT.
There are certain medications that make PSVT more likely.
For example, when taken in large doses, the heart medication digitalis
(digoxin) can lead to episodes of PSVT. The following actions can also increase
your risk of having an episode of PSVT:
ingesting caffeine
ingesting alcohol
smoking
using illegal
drugs
taking certain
allergy and cough medications
What are the symptoms of paroxysmal supraventricular
tachycardia?
The symptoms of PSVT resemble the symptoms of an anxiety
attack and can include:
heart palpitations
a rapid pulse
a feeling of
tightness or pain in the chest
anxiety
shortness of
breath
In more serious cases, PSVT can cause dizziness and even
fainting due to poor blood flow to the brain.
Sometimes, a person experiencing symptoms of PSVT may
confuse the condition with a heart attack. This is especially true if it’s
their first PSVT episode. If your chest pain is severe you should always go to
the emergency room for testing.
How is paroxysmal supraventricular tachycardia diagnosed?
If you have an episode of fast heartbeats during an
examination, your doctor will be able to measure your heart rate. If it’s very
high, they may suspect PSVT.
To diagnose PSVT, your doctor will order an
electrocardiogram (EKG). This is an electrical tracing of the heart. It can
help determine which type of rhythm problem is causing your fast heart rate.
PSVT is only one of many causes of abnormally fast heartbeats. Your doctor will
also likely order an echocardiogram, or ultrasound of the heart, to evaluate
the size, movement, and structure of your heart.
If you have an abnormal heart rhythm or rate, your doctor
may refer you to a specialist who is an expert in electrical problems of the
heart. They are known as electrophysiologists or EP cardiologists. They may
perform an electrophysiology study (EPS). This will involve threading wires
through a vein in your groin and up into your heart. This will allow your
doctor to evaluate your heart’s rhythm by checking the electrical pathways of
your heart.
Your doctor may also monitor your heart rate over a period
of time. In this case, you may wear a Holter monitor for 24 hours or longer.
During that time, you’ll have sensors attached to your chest and will wear a
small device that records your heart rate. Your doctor will assess the
recordings to determine if you have PSVT or some other type of abnormal rhythm.
How is paroxysmal supraventricular tachycardia treated?
You might not need treatment if your symptoms are minimal or
if you only have episodes of rapid heart rate occasionally. Treatment may be
necessary if you have an underlying condition causing the PSVT or more severe
symptoms like heart failure or passing out.
If you have a rapid heart rate but your symptoms aren’t
severe, your doctor can show you techniques to return your heart rate to
normal. It’s called the Valsalva maneuver. It involves closing your mouth and
pinching your nose while trying to exhale and straining as if you were trying
to have a bowel movement. You should do this while sitting and bending your
body forward.
You can perform this maneuver at home. It may work up to 50
percent of the time. You can also try coughing while sitting and bending
forward. Splashing ice water on your face is another technique to help lower
your heart rate.
Treatments for PSVT include medications, such as or
flecainide or propafenone, to help regulate your heartbeat. A procedure called
radiofrequency catheter ablation is a common way to correct PSVT permanently.
It’s performed in the same way as an EPS. It allows your doctor to use
electrodes to disable the electrical pathway that’s causing the PSVT.
If your PSVT doesn’t respond to other treatments, your
doctor may surgically implant a pacemaker into your chest to regulate your
heart rate.
Things You Can Do for Rapid Heartbeat:
Make sure you tell your doctor, as well as all healthcare providers, about any other
medications you are taking (including over-the-counter, vitamins, or herbal remedies).
Do not take aspirin or products containing aspirin unless your healthcare provider
permits this.
Remind your doctor or healthcare provider if you have a history of diabetes, liver,
kidney, or heart disease.
If you have a family history of heart disease, stroke, high blood cholesterol, or
high blood pressure, in a first or second-degree relative, you may be at risk for
certain problems. Notify your healthcare provider if you have any of these diseases
in your family.
Smoking can cause palpitations and increased heart rate. If you smoke, be sure to
quit. Smoking can also increase the chance of developing heart vessel damage.
Caffeine and alcohol can cause palpitations and increased heart rate. Eliminate
caffeine and alcohol from your diet, and your symptoms may resolve.
Keep a diary of your increased heart rate, if it is occurring regularly. Write down
the foods that you have eaten, the exercise or activity you were undergoing when
the rapid or irregular heartbeats occurred, and how you felt before they occurred.
This diary may be valuable in determining the cause of your symptoms.
Questions to ask yourself, may include:
Did the increased heart rate occur gradually, or did this episode come on all of
a sudden? Was I feeling anxious? Did I perform any kind of activity, or was I resting?
Make sure to exercise, under the supervision of your healthcare provider. Walking,
swimming, or light aerobic activity may decrease your resting heart rate, help you
to lose weight, and promote the flow of oxygen in your lungs and blood.
Use relaxation techniques to decrease the amount of anxiety you have. If you feel
anxious, place yourself in a quiet environment, and close your eyes. Take slow,
steady, deep breaths, and try to concentrate on things that have relaxed you in
the past.
If you are ordered a medication to treat this disorder, do not stop taking any medication
unless your healthcare provider tells you to. Take the medication exactly as directed.
Do not share your pills with anyone.
If you miss a dose of your medication, discuss with your healthcare provider what
you should do.
If you experience symptoms or side effects, especially if severe, be sure to discuss
them with your health care team. They can prescribe medications and/or offer
other suggestions that are effective in managing such problems.
Keep all your appointments for your treatments.
Drugs That May Be Prescribed by Your Doctor:
ACE inhibitors - These drugs work by opening, or dilating, your
arteries. They will lower your blood pressure, and improve blood flow to your kidneys,
and through out your body. Your healthcare provider may also prescribe these medications
if you have diabetes or protein in your urine, to protect your kidneys. Some examples
of this medication may include: Enalapril Maleate (Vasotec®),
Lisinopril (Zestril®), and Fosinopril Sodium (Monopril®)
Antianxiety medications: If your increased heart rate is due to
anxiety, your healthcare provider may prescribe an anti-anxiety medication, called
an anxiolytic. These medications will help you to relax. It is important to
take these medications only when you are feeling anxious. Do not operate heavy machinery,
or drive an automobile while taking these. If these medications do not control your
symptoms, discuss this with your doctor.
Beta-blockers - can be used to slow down your heart rate, and improve
blood flow through your body. You may take this drug if you have been diagnosed
with irregular heartbeats, or high blood pressure. Some examples of this medication
may include: Metoprolol (Lopressor®), propanolol
(Inderal®), and atenolol (Tenormin®).
Calcium Channel Blockers - These medications may be given to treat
chest pain, high blood pressure, or irregular heart beats. This medication will
slow your heart rate. A few common drugs include Verapamil HCL (Calan®),
and Diltiazem (Dilacor XR®).
Digoxin - Also called digitalis, this medication works by slowing
down the heart rate, and making it beat more effectively. This will pump blood through
out the body better. It is also called Lanoxin®.
Diuretics - may be known as "water pills", as they work to prevent
heart failure by making you urinate out extra fluid. Some examples of this medication
may include furosemide (Lasix®), and Hydrochlorthiazide.
You may receive this medication alone or in combination with other medications.
Do not stop any of these medications abruptly, as serious side effects may occur.
இங்கிலாந்தின் பிரபல கம்பெனி ஒன்றிற்கு, பெரியதோர் இயந்திரம் ஜப்பானில்
இருந்து வரவழைக்கப்பட்டது. கோடிக்கணக்கில் விலை. அந்த இயந்திரத்தை
இன்ஸ்டால் செய்ய ஜப்பானில் இருந்து ஒரு குழு வந்திருந்தது. அதில் ஒரு 20
வயது மதிக்கத்தக்க ஒருவன். துறுதுறுவென்று எல்லாரிடமும், பேசிக்கொண்டும்
சிரித்துக் கொண்டுமிருக்கிறான். இங்கிலாந்து கம்பெனியின் நிர்வாகிக்கு அந்தச் சிறுவனைக் கண்டதுமே ஏனோ பிடிக்கவில்லை. இரண்டொரு நாளில் இன்ஸ்டலேஷன் பணிகள் துவங்க இருக்க, ஜப்பான் நிறுவனத்திற்கு மின்னஞ்சல் அனுப்புகிறார்.
“ஏப்பா.. அவ்ளோ துட்டுப் போட்டு வாங்கிருக்கோம். சர்வீஸ் டீம்ல
சின்னப்பையனைலாம் சேர்த்தி அனுப்பிருக்கீங்க? என்ன டூர் வந்திருக்காங்களா?
ஏர்போர்ட்ல இருந்து ரூமுக்கு அனுப்ச்சாச்சு. நாளைன்னைக்கு இன்ஸ்டால்
பண்றப்ப அந்தப் பையன் மிஷின்ல கைய வைக்கக்கூடாது ஆமா. அதென்ன
சின்னப்புள்ளைக சமாச்சாரமா?” - இதுதான் அவர் அனுப்பிய மின்னஞ்சலின்
சாராம்சம். உடனடியாக பதில் அஞ்சல் வந்தது. “மன்னிக்க வேண்டும்.
தவறுதான். நாங்கள், அந்தச் சிறுவனுக்கு பதில் கொஞ்சம் சீனியரை டீமுக்கு
அனுப்புகிறோம். அந்தச் சிறுவன் அங்கே இருப்பான். ஆனால் கருவியைக் கையாள
மாட்டான்” என்று பதில் வருகிறது. சொன்னபடியே கொஞ்சம் வயதில் மூத்தவர்
வருகிறார். குழுவுடன் இணைந்து பணியாற்றுகிறார். அந்தச் சிறுவனும்
அவர்களுடன்தான் இருக்கிறான். ஆனால் அந்த மிஷின் வேலை செய்யும்
இடத்திலிருந்து கொஞ்சம் தள்ளியே அமர்ந்திருக்கிறான். இந்தக் குழுவினார் டீ
ப்ரேக், லஞ்ச் ப்ரேக்கெல்லாம் ஒன்றாக அமர்ந்து பேசிக் கொண்டிருந்து, இரண்டு
நாட்களில் இயந்திரத்தை நிறுவிவிடுகிறார்கள். வேலை வெற்றிகரமாக
முடிந்துவிடுகிறது. வழியனுப்பும்போது, இந்த இங்கிலாந்து கம்பெனி
நிர்வாகிக்கு சின்னதாக ஒரு குற்ற உணர்வு. என்ன இருந்தாலும் அவ்வளவு
கடுமையாக மின்னஞ்சல் அனுப்பியிருக்கக்கூடாது என்று தோன்றுகிறது. அந்தச்
சிறுவன் அவன் பாட்டுக்கு சிரித்த முகத்துடனேயே வளைய வருகிறான். அவனிடம்
இதைச் சொல்லிவிட்டால் மனது லேசாகிவிடும் என்று உணர்கிறார். குழுவினர்
எல்லாரும் இருக்க, சொல்கிறார்: “ஸாரி.. ஆக்சுவலி பலகோடி ரூபாய்
ப்ராஜக்ட். இன்ஸ்டால் பண்றப்ப எதும் சிக்கல் வந்தா அப்பறம், பணம் நேரம்னு
பெரிய நஷ்டமாகிடும். அதான் கொஞ்சம் சீனியர் வேணும்னு கேட்டேன். மத்தபடி ஐ
லைக் த பாய். துறுதுறுன்னு இருக்கான். ஆனா இந்த டீம்ல இப்படி ஒரு
சின்னப்பையன் வந்தது எனக்கு சரின்னு படலை. அதான்..” என்று பாலிஷாகச்
சொல்கிறார். அந்தச் சிறுவன் அதே புன்னகையுடனே இருக்க, புதிதாக
வந்தவர் சொல்கிறார். “இட்ஸ் ஓகே சார். நாங்க வாடிக்கையாளர் கருத்துக்கு
ரொம்ப முக்கியத்துவம் கொடுப்போம். நீங்க சொன்னதுமே என்னை அனுப்பி
வெச்சாங்க. இப்ப மிஷின் நல்லபடியா இன்ஸ்டால் செஞ்சு, ஓடிட்டிருக்கு. ஆனா
ஒரு விஷயம்..” தயங்குகிறார். ”பரவால்ல.. எதாருந்தாலும் சொல்லுங்க” “நான் அந்தக் கம்பெனில அக்கவுண்ட்ஸ்ல வொர்க் பண்ற ஆளுதான். எனக்கு இந்த மிஷின் பத்தி ஏபிசிடிகூட தெரியாது” நிர்வாகி அதிர்ச்சியாகிறார். “அப்பறம் இன்ஸ்டலேஷனப்ப வேலை செஞ்சுட்டிருந்தீங்க?” “இந்தப் பையன்கிட்ட போய்ப் போய்க் கேட்டு அவன் சொல்றத மட்டும் பண்ணினேன் அவ்ளதான்” “அந்தப் பையன் எப்படி மிஷின் பக்கமே வராம, உங்களுக்கு இன்ஸ்ட்ரக்ஷன்ஸ் குடுத்திருக்கமுடியும்?” “முடியும். ஏன்னா, இந்த மிஷினைக் கண்டுபிடிச்சதே அவன்தான்”
அரசு பணியில் ஒரு பெரும் அதிகாரியாக அமர்ந்து உள்ளீர்கள்.. கோடிக்கணக்கான
பணம், செல்வம், வீடு, நிலம் என நீங்கள் கேட்கும் அத்தனையும் உங்கள்
காலடியில் இலஞ்சமாக கொட்ட படுகிறது... நீங்கள் செய்ய வேண்டியது ஒன்றே ஒன்று...ஒரு கையெழுத்து...
புதிதாக சந்தையில் வந்த ஒரு மருந்தை நம் நாட்டில் மக்கள் பயண்படுத்தலாம்
அது பாதுகாப்பானதுதான் என்ற அனுமதி கையெழுத்து மட்டும் நீங்கள் போட
வேண்டும்... பாதுகாப்பிற்கான மருத்துவ ஆய்வு ஆதாரங்களை அந்த கார்ப்பெரேட் மருத்துவ கம்பெனி இன்னமும் சமர்ப்பிக்க வில்லை... ஆனால் கோடிகளில் புரளும் அந்த கம்பெனி உங்களுக்கு பணத்தை காட்டி மயக்குகிறான் உங்கள் நண்பர்களெல்லாம் கையெழுத்து போட்டு பணம் பார்த்து விட்டார்கள்... உங்கள் நிலை என்னவாக இருக்கும்?
நான் கற்ற மருந்தியல் அறிவியல் மக்களுக்கு பயண்பட வேண்டும்...ஆய்வு
ஆதாரங்கள் இன்றி நான் எந்த மருந்தையையும் நம் நாட்டில் அனுமதிக்க மாட்டேன்!
என்ற கருத்தா? அல்லது அறிவியலாவது டேஷ் ஆவது...எவனோ என்னமோ செய்கிறான் நமக்கென்ன? நாலு காசு பார்த்து செட்டிலாவோம் என்ற சிந்தனையா?? சிந்தியுங்கள்...
இதே நிலை 1960 களில் அமெரிக்காவை சேர்ந்த பிரான்சிஸ் கேத்லீன் ஓல்டஹாம் (
Francis Kathleen Oldham) என்ற பெண் அமெரிக்காவின் மருந்து மற்றும் உணவு
மேலாண்மை (FDA- Food and Drug Administration) துறை உயர் அதிகாரியாக
இருந்தவருக்கு வந்தது... அந்த துறையில் இவர் பதவியில் இவர்
மட்டுமே ஒரே பெண் அதிகாரி. அதுவே அக்காலத்தில் பலருக்கு கடுப்பு. மேலும்
அவர் மிக நேர்மையான அதிகாரி. மேற்கு ஜெர்மன் நாட்டு மருந்து
கம்பெனியான கெமி குருனென்தல் (Chemie Grünenthal) கர்பமான பெண்களின்
தலைசுற்றல் வாந்தி மயக்கம் போன்றவை தடுக்க தளிடோமைட் (Thalidomide) என்ற
மருந்து கண்டுபிடித்து ஐரோப்பிய முழுவதும் அமோகமாக விற்பனை செய்தது. அந்த
மருந்தை பல கோடி டாலர்கள் பணம் கொடுத்து அமெரிக்கா கார்ப்பரேட் மருத்துவ
கம்பெனியான மரியோன் ஆய்வகம் (Marion Laboratoires) அமெரிக்காவில் விற்க
உரிமைகளை வாங்கியது. ஆனால் அமெரிக்காவினுள் அந்த மருந்தை பயண்படுத்த அரசாங்க அனுமதி வேண்டும். அதற்கு கேத்லீனின் அனுமதி கையொப்பம் வேண்டும். கேத்லீனின் சக அதிகாரகளெல்லாம் காசு வாங்கிய நிலையில் கேத்லீன் மட்டுமே கையொப்பம் இட மறுத்தார்...
அந்த மருந்து பாதுகாப்பானது தான் என்ற குறைந்த பட்சம் விலங்குகள் மீதான
ஆய்வு ஆதாரங்கள் எங்கே? அதை காட்டுங்கள்..அதை படித்து விட்டு அனுமதி
தருகிறேன் என்றார்... எவ்வளவு காசு பணம் வீடு நிலம் என ஆசை காட்டியும் அவர் திட்டவட்டமாக ஆதாரம் இல்லாமல் அனுமதிக்க மறுத்து விட்டார்.
அண்டை நாடான கேனடா, மேற்கு ஐரோப்பா நாடுகள் என அனைத்து வளர்ந்த நாடுகளும்
பயண்படுத்துகின்றன நீங்கள் மட்டும் ஏன் பிடிவாதம் பிடிக்கிறீர்கள்? என்று
கேட்டனர் கார்ப்பரேட் முதலாளிகள். அவர் மசியவில்லை. 7 முறை அந்த கம்பெனி அந்த மருந்தை விற்க விண்ணப்பத்தும் 7 முறையும் நிராகரித்து விட்டார்... ஓரிரு ஆண்டுகளுக்குள் கேனடா, ஆஸ்திரேலியா, மேற்கு ஐரோப்பா நாடுகள் என பல நாடுகளிலிருந்தும் திடிக்கிடும் தகவல் வந்தது.
தளிடோமைடை கர்ப்ப காலத்தில் உண்ட பெண்களுக்கு குழந்தைகள் ஊனமுற்ற
பிறக்கிறார்கள் என்ற தகவல். சூம்பிபோன கைகால்களுடன் உலகம் முழுவதும்
கிட்டத்தட்ட 20,000 குழந்தைகள் பிறந்தன..அதற்கு காரணம் தளிடோமைட் மருந்தால்
தொப்பில் கொடி வழியாக கருவுக்கு சென்று கரு வளர்ச்சியில் பாதிப்பை
ஏற்படுத்தும் என்ற உண்மையை கண்டனர்... தளிடோமைட் தயாரித்த ஜெர்மானிய கம்பெனி கடும் நஷ்டத்தில் வீழ்ந்தது. கேத்லீன் அந்த மருந்தை எல்லைகளிலேயே தடுத்ததால் பல்லாயிர குழுந்தைகள்
அமெரிக்காவில் காப்பாற்ற பட்டனர் என்ற உண்மையை அறிந்த கென்னடி அரசாங்கம்
கேத்லீனுக்கு நாட்டின் உயர்ந்த குடிமகள் என்ற விருதை 1965 வழங்கியது... கேத்லீன் 107 வயது வரை வாழ்ந்து 2015 இல் தான் இறந்தார். அந்த அம்மையார் பணத்தாசையில் மயங்காமல் அறிவியலின் பக்கமே நின்று மக்களை பாதுகாத்ததால் நம் குழு அவருக்கு தலை வணங்குகிறது....
அறிவியல் ஆதாரமா? இல்லை பணமா? என்றால் அறிவியல் ஆதாரங்களையே தேர்வு செய்ய
வேண்டும் என்று மிக சிறந்த முன்மாதிரியாக வாழ்ந்து காட்டியவருக்கு இந்த
மருத்துவர் தினத்தில் நம் வணக்கங்கள்
Since the beginning of the 20th century, as the automobile
and truck have offered ever higher levels of mobility, vehicle ownership per
head of population has increased. Road needs have been strongly influenced by
this popularity and also by the mass movement of people to cities and thence to
suburban fringes—a trend that has led to increasing travel needs and road
congestion and to low-density cities, which are difficult to service by public
transport. Often the building of new roads to alleviate such problems has
encouraged further urban sprawl and yet more road travel. Long-term solutions
require the provision of alternatives to car and truck transport, controls over
land use, and the proper pricing of road travel. To this end, road managers
must be concerned not merely with lines on maps but also with the number, type,
speed, and loading of individual vehicles, the safety, comfort, and convenience
of the traveling public, and the health and welfare of bystanders and adjoining
property owners.
Ideally, the development of a major road system is an
orderly, continuous process. The process follows several steps: assessing road
needs and transport options; planning a system to meet those needs; designing
an economically, socially, and environmentally acceptable set of roads;
obtaining the required approval and financing; building, operating, and
maintaining the system; and providing for future extensions and reconstruction.
Planning
Road needs are closely associated with the relative location
of centres of population, commerce, industry, and transportation. Traffic
between two centres is approximately proportional to their populations and
inversely proportional to the distance between them. Estimating traffic on a
route thus requires a prediction of future population growth and economic
activity, an estimation of their effects on land use and travel needs, and a
knowledge of any potential transport alternatives. The key variables defining
road needs are the traffic volumes, tonnages, and speeds to be expected
throughout the road’s life.
Once the traffic demand has been estimated, it is necessary
to predict the extent of the road works needed to handle that traffic. A
starting point in these calculations is offered by surveys of the origins,
destinations, and route choices of present traffic; computer models are then
used to estimate future traffic volumes on each proposed route. Estimates of
route choice are based on the understanding that most drivers select their
estimate of the quickest, shortest, or cheapest route. Consideration in
planning is also given to the effect of new traffic on existing streets, roads,
and parking provisions.
Where feasible, the next step in planning a road system is
to refine the selected route to a narrow corridor. The various alignment
options are drawn, considering the local terrain and conditions. The economic,
social, and environmental benefits and costs of these options are discussed
with relevant official and community groups until an acceptable specific route
is determined.
Road design
Alignment and profile
After a route has been selected, a three-dimensional road
alignment and its associated cross-sectional profiles are produced. In order to
reduce the amount of earth to be moved, the alignment is adjusted where practical
so that the earth to be excavated is in balance with the embankments to be
built. Computers allow many options to be explored and realistic views of the
future road to be examined.
In order to fully understand the design stage, a few
standard terms must be defined (see figure). A traffic lane is the portion of
pavement allocated to a single line of vehicles; it is indicated on the
pavement by painted longitudinal lines or embedded markers. The shoulder is a
strip of pavement outside an outer lane; it is provided for emergency use by
traffic and to protect the pavement edges from traffic damage. A set of
adjoining lanes and shoulders is called a roadway or carriageway, while the
pavement, shoulders, and bordering roadside up to adjacent property lines are
known as the right-of-way.
Schematic cross section of a modern roadway.
Schematic cross section of a modern roadway.
Encyclopædia Britannica, Inc.
In order to maintain quality and uniformity, design
standards are established for each functional road type. The number of traffic
lanes is directly determined by the combination of traffic volume and speed,
since practical limits on vehicle spacing means that there is a maximum number
of vehicles per hour that pass through a traffic lane. The width of lanes and
shoulders, which must strike a balance between construction cost and driver
comfort, allows the carriageway width to be determined. Standards also specify
roadside barriers or give the clear transverse distances needed on either side
of the carriageway in order to provide safety in the event that vehicles
accidentally leave the carriageway. Thus it is possible to define the total
right-of-way width needed for the entire road, although intersections will add
further special demands.
Design standards also help to determine the actual alignment
of the road by specifying, for each design speed, the minimum radius of
horizontal curves, the maximum vertical gradient, the clearance under bridges,
and the distance a driver must be able to see the pavement ahead in order to
stop or turn aside.
Pavement
Road traffic is carried by the pavement, which in
engineering terms is a horizontal structure supported by in situ natural
material. In order to design this structure, existing records must be examined
and subsurface explorations conducted. The engineering properties of the local
rock and soil are established, particularly with respect to strength,
stiffness, durability, susceptibility to moisture, and propensity to shrink and
swell over time. The relevant properties are determined either by field tests
(typically by measuring deflection under a loaded plate or the penetration of a
rod), by empirical estimates based on the soil type, or by laboratory
measurements. The material is tested in its weakest expected condition, usually
at its highest probable moisture content. Probable performance under traffic is
then determined. Soils unsuitable for the final pavement are identified for
removal, suitable replacement materials are earmarked, the maximum slopes of
embankments and cuttings are established, the degree of compaction to be
achieved during construction is determined, and drainage needs are specified.
In a typical rural pavement (as shown in the figure), the
top layer of the pavement is the wearing course. Made of compacted stone,
asphalt, or concrete, the wearing course directly supports the vehicle,
provides a surface of sufficient smoothness and traction, and protects the base
course and natural formation from excessive amounts of water. The base course
provides the required supplement to the strength, stiffness, and durability of
the natural formation. Its thickness ranges from 4 inches (10 centimetres) for
very light traffic and a good natural formation to more than 40 inches (100
centimetres) for heavy traffic and a poor natural formation. The subbase is a
protective layer and temporary working platform sometimes placed between the
base course and the natural formation.
Pavements are called either flexible or rigid, according to
their relative flexural stiffness. Flexible pavements (see figure, left) have
base courses of broken stone pieces either compacted into place in the style of
McAdam or glued together with bitumen to form asphalt. In order to maintain
workability, the stones are usually less than 1.5 inches in size and often less
than 1 inch. Initially the bitumen must be heated to temperatures of 300°–400°
F (150°–200° C) in order to make it fluid enough to mix with the stone. At the
road site a paving machine places the hot mix in layers about twice the
thickness of the stone size. The layers are then thoroughly rolled before the
mix cools and solidifies. In order to avoid the expense of heating, increasing
use has been made of bitumen emulsions or cutbacks, in which the bitumen binder
is either treated with an emulsifier or thinned with a lighter petroleum
fraction that evaporates after rolling. These treatments allow asphalts to be
mixed and placed at ambient temperatures.
Cross sections of modern pavements(Left) Flexible
asphalt-based pavement. (Right) Rigid portland-cement concrete pavement.
Cross sections of modern pavements(Left) Flexible
asphalt-based pavement. (Right) Rigid portland-cement concrete pavement.
Encyclopædia Britannica, Inc.
The surface course of a flexible pavement protects the
underlying base course from traffic and water while also providing adequate
tire friction, generating minimal noise in urban areas, and giving suitable
light reflectance for night-time driving. Such surfaces are provided either by
a bituminous film coated with stone (called a spray-and-chip seal) or by a thin
asphalt layer. The spray-and-chip seal is used over McAdam-style base courses
for light to moderate traffic volumes or to rehabilitate existing asphalt
surfaces. It is relatively cheap, effective, and impermeable and lasts about 10
years. Its main disadvantage is its high noise generation. Maintenance usually
involves further spray coating with a surface dressing of bitumen. Asphalt
surfacing is used with higher traffic volumes or in urban areas. Surfacing
asphalt commonly contains smaller and more wear-resistant stones than the base
course and employs relatively more bitumen. It is better able to resist
horizontal forces and produces less noise than a spray-and-chip seal.
Rigid pavements (see figure, right) are made of portland
cement concrete. The concrete slab ranges in thickness from 6 to 14 inches. It
is laid by a paving machine, often on a supporting layer that prevents the
pressure caused by traffic from pumping water and natural formation material to
the surface through joints and cracks. Concrete shrinks as it hardens, and this
shrinkage is resisted by friction from the underlying layer, causing cracks to
appear in the concrete. Cracking is usually controlled by adding steel
reinforcement in order to enhance the tensile strength of the pavement and
ensure that any cracking is fine and uniformly distributed. Transverse joints
are sometimes also used for this purpose. Longitudinal joints are used at the
edge of the construction run when the whole carriageway cannot be cast in one
pass of the paving machine.
In places where the local natural material is substandard
for use as a base course, it can be “stabilized” with relatively small
quantities of lime, portland cement, pozzolana, or bitumen. The strength and
stiffness of the mix are increased by the surface reactivity of the additive,
which also reduces the material’s permeability and hence its susceptibility to water.
Special machines distribute the stabilizer into the upper 8 to 20 inches of
soil.
In deciding whether to use a flexible, rigid, or stabilized
pavement, engineers take into account lifetime cost, riding characteristics,
traffic disruptions due to maintenance, ease and cost of repair, and the effect
of climatic conditions. Often there is little to choose between rigid and
flexible pavements.
The properties of the base course material are usually
determined by laboratory tests, although field tests are sometimes conducted to
check that the construction process has achieved the designer’s intent.
Designers typically consider the possibility of structural failure resulting
from a single overload and also from damage accumulating under the passage of
many routine loads. Both of these types of failure are almost entirely caused
by trucks.
Drainage
Adequate drainage is the single most important element in
pavement performance, and drainage systems can be extensive and expensive.
Drainage involves handling existing watercourses, removing water from the
pavement surface, and controlling underground water in the pavement structure.
In designing the system, the engineer first selects the “design storm”—that is,
the most severe flood that can be expected in a nominated period of time (as
much as 100 years for a major road or as little as 5 years for a minor street
carrying local traffic). The drainage system must be able to carry the storm
water produced by this design storm without flooding the roadway or adjacent property.
In areas where land use is changing from agricultural to residential or
commercial, peak flows will increase notably as the surrounding area is covered
with roofs and paving.
Safety requires that water be rapidly removed from the
pavement surface. In urban areas, the water runs into shallow gutters and
thence into the inlets of underground drains. In rural areas, surface water
flows beyond the shoulders to longitudinal drainage ditches, which have flat
side slopes to enable vehicles leaving the pavement to recover without serious
incident. Cut-off surface drains are used to prevent water from flowing without
restriction down the slopes of cuttings and embankments.
Vertical drainage layers, formed from single-sized aggregate
or special sheets called geofabrics and geomembranes, are used to prevent
groundwater from seeping laterally into the pavement structure. In addition, a
horizontal drainage layer is often inserted between base course and natural
ground in order to remove water from the pavement structure and stop upward
capillary movement of any natural groundwater. Underground drains can also be
used to lower the groundwater level by both preventing water entry and removing
water that does enter the pavement structure.
Financing
The full design of a proposed road is analyzed with respect
to its costs and its economic, social, and environmental effects. It may also
be subjected to public review. This step can be lengthy, as new roads are
usually popular with the traveling public but sometimes cause distress in the
communities through which they pass.
Local streets and collector roads are usually administered
by local governments and financed by local taxes. Arterial roads and highways,
however, need a wider administrative and financial input in order to guarantee
route continuity and uniformity. Since the 1920s the financing of roads has
been largely transferred to the road user. A variety of taxes is employed: on
fuel and oil, on road usage, on vehicle purchase and ownership, on driver
licensing, on truck mass and mass times distance traveled, on tire and
accessory purchases, and on the economic benefits provided by roads (e.g.,
higher property values or increased productivity). Fuel taxes usually provide
the simplest source of revenue, but they are not necessarily intended solely
for expenditure on roads. Many local roads are funded by property taxes.
Construction
After the road has been approved and financing found,
surveyors define its three-dimensional location on the ground. Forming of the in-situ
material to its required shape and installation of the underground drainage
system can then begin. Imported pavement material is placed on the natural
formation and may have water added; rollers are then used to compact the
material to the required density. If possible, some traffic is permitted to
operate over the completed earthwork in order to detect weak spots.
In countries where labour is inexpensive and less skilled,
traditional manual methods of road construction are still commonplace. However,
the developed world relies heavily on purpose-built construction plant. This
can be divided into equipment for six major construction purposes: clearing,
earthmoving, shaping, and compacting the natural formation; installing
underground drainage; producing and handling the road-making aggregate;
manufacturing asphalt and concrete; placing and compacting the pavement layers;
and constructing bridges and culverts.
For clearing vegetation and undesirable materials from the
roadway, the bulldozer is often employed. The construction of rock cuts is
commonly done with shovels, draglines, and mobile drills. Shaping the formation
and moving earth from cuttings to embankments is accomplished with bulldozers,
graders, hauling scrapers, elevating graders, loaders, and large dump trucks.
The material is placed in layers, brought to the proper moisture content, and
compacted to the required density. Compaction is accomplished with tamping,
sheeps-foot, grid, steel-wheeled, vibrating, and pneumatic-tired rollers.
Backhoes, back actors, and trenchers are used for drainage work.
In order to avoid high haulage costs, the materials used for
base course construction are preferably located near the construction site; it
is economically impossible to use expensive materials for long lengths of road
construction. The excavation process is the same as for rock cuts, although
rippers may be used for obtaining lower-grade material. Crushers, screens, and
washers produce stone of the right size, shape, and cleanliness.
The placement of paving material increasingly involves a
paving machine for distributing the aggregate, asphalt, or concrete uniformly
and to the required thickness, shape, and width (typically, one or two traffic
lanes). The paving machine can slipform the edges of the course, thus avoiding
the need for fixed side-forms. As it progresses down the road, it applies some
preliminary compaction and also screeds and finishes the pavement surface. In
modern machines, level control is by laser sighting.
In producing a spray-and-chip seal surface (or a bituminous
surface treatment), a porous existing surface is covered with a film of hot, fluid
bitumen that is sprayed in sufficient quantity to fill voids, cracks, and
crevices without leaving excess bitumen on the surface. The surface is then
sprayed with a more viscous hot bitumen, which is immediately covered with a
layer of uniform-size stone chips spread from a dump truck. The roadway is then
rolled to seat the stone in the sticky bitumen, and excess stone is later
cleared by a rotary broom.
Maintenance
The life of a road structure depends on the quality of its
maintenance and minor renovation. Maintenance keeps the roadway safe, provides
good driving conditions, and prolongs the life of the pavement, thus protecting
the road investment. Maintenance consists of activities concerned with the
condition of the pavement, shoulders, drainage, traffic facilities, and
right-of-way. It includes the prompt sealing of cracks and filling of potholes
to prevent water entering through the surface, the removal of trash thrown on
the wayside by the traveling public, and the care of pavement markings, signs,
and signals. In rigorous winter climates, substantial effort is required to
remove snow and ice from the pavement, to scatter salt for snow and ice
removal, and to spread sand for better traction.
Road operation
Traffic management
Road users are subject to traffic control via instructions
and information provided by roadway markings, signs, and signals, and they are
subject to legal control via the rules of the road (particularly those
concerned with vehicular priority).
Traffic control
The marking of roadway surfaces with painted lines and
raised permanent markers is commonplace and effective, despite high maintenance
costs and visibility problems at night, in heavy traffic, and in rain or snow.
A solid line is a warning or instruction not to cross, and a broken line is for
guidance. Thus, solid lines indicate dangerous conditions (such as restricted
sight distance where overtaking would be dangerous), pavement edges, stop
lines, and turning lanes at intersections; broken lines indicate interior lane
lines and centre lines on two-way roads where the sight distance is good. Lines
are usually white, but yellow is used for centre lines in North America.
Signs advise the driver of special regulations and provide
information about hazards and navigation. They are classified as regulatory
signs, which provide notice of traffic laws and regulations (e.g., signs for
speed limits and for stop, yield or give-way, and no entry); warning signs,
which call attention to hazardous conditions (e.g., sharp curves, steep grades,
low vertical clearances, and slippery surfaces); and guide signs, which give
route information (e.g., numbers or designations, distances, directions, and
points of interest).
Signs have standard shapes and colours—for instance, the red
octagon used for the stop sign, the triangle for warning signs, the green
rectangle with white lettering for freeway directional signs (commonly mounted
over the roadway and of large size for easy reading at high speeds). Tourist
signs are brown rectangles, and special shapes and colours are used for route
markers. Many signs, such as the stop sign, are universally used, but there are
some differences between the two common international systems based on either
the American or the European practice. Basically, these differences are derived
from a complete reliance on symbolic signs and a greater range of blue guidance
signs in multilingual Europe.
Traffic signals are primarily used to control traffic in
urban street systems—particularly at conventional intersections accommodating
large traffic volumes, where they allocate right-of-way to the various traffic
streams. They can also meter traffic entering access lanes onto busy freeways
or to indicate the lanes to use on two-way roads. Simple traffic signals work
on preset timing plans that vary with the time of day. More advanced
traffic-actuated signals automatically monitor the traffic streams and allocate
right-of-way accordingly. Signals can also be linked to a computer so that
traffic traveling along a major route can receive a continuous wave of green
signals, obtaining maximum traffic output from the system.
Legal control
Legal rules governing the movement of traffic are an
essential part of order on the road. The rules may be divided into three
categories. First are those applying to the vehicle and the driver, such as
vehicle and driver registration, vehicle safety equipment and roadworthiness,
accident reporting, financial liability, and truck weights and axle loads (to
protect pavements and bridges from damage). Second are the movement rules for
drivers and pedestrians, known as the rules of the road; these dictate which
side of the road to use, maximum speeds, right-of-way, and turning
requirements. Third are those regulations that apply to limited road sections,
indicating speed limits, one-way operations, and turning controls.
The important rules of the road are reasonably uniform
throughout the world. For instance, in most countries drivers must give
right-of-way to vehicles on their right. However, in practice the stop and
yield (or give-way) signs have commonly supplanted the right-of-way rule. Speed
limits vary greatly with jurisdiction, ranging from walking pace in a Dutch
woonerf, or “shared” street, to unrestricted on a German autobahn. Speed limits
are commonly reduced on roads approaching residential, shopping, or school
areas and on dangerous road sections and sharp curves.
Special regulations are important for the efficient movement
of traffic in specific segments of a street and road system. For instance,
one-way streets in congested urban areas may provide safer driving conditions
and increase the traffic-carrying capacity of the system. The provision of
special turn arrows in traffic signals or the prohibition of turns at
intersections contribute to safety, increase traffic throughput, and reduce
conflict.
Safety
Traffic police (or road patrols or highway police) help
improve road safety and traffic flow by enforcing driving regulations. They
also regulate traffic at the scene of an accident and investigate accidents.
Traffic enforcement has been aided by the use of technology—cameras, radar,
video, and inductance loops—to detect and record traffic offenders
automatically.
An important aspect of traffic regulation and accident
prevention is the control of excessive speed, which contributes significantly
to the number and severity of road crashes. Speed is commonly measured by radar
devices or by pacing with a patrol car. In crash investigations, the speed of
the cars is determined by the length of skid marks. Another key factor in road
accidents is the influence of alcohol and drugs. Tests for intoxication are now
widely conducted; the most common is the breath test, in which the driver blows
into a device that analyzes the alcohol content of the breath and indicates the
approximate blood alcohol level. Many authorities believe that 0.50 gram of
alcohol per litre of blood is a realistic limit for ordinary motorists, but
that zero levels should be demanded for critical operators such as drivers of
public transport vehicles.
Road safety can also be built into the road. Divided roads
are many times safer than two-way roads. Crash severity can be reduced by the
use of “soft” signs and light poles and by guardrails and impact attenuators in
front of fixed roadside objects such as bridge piers and the noses at the exit
ramps of a freeway. Better road surfaces, alignments, signing, and marking
improve driving conditions and increase road safety.
Nevertheless, about 90 percent of crashes are primarily due
to human error. Many crashes have been attributed to simple inattention or
failure to see warnings. Alcohol, fatigue, inexperience, aggression, and
excessive risk taking are the most common crash causes involving behavioral
changes in drivers. Lack of driving skills is rarely an issue; most drivers do
not need training as much as they need education and experience. Meanwhile,
road engineers must design road systems that attempt to reduce the frequency
and impact of human error.
பலர் என்னிடம் கேட்கும் கேள்வி „சொந்தமாக தொழில் தொடங்க இருப்பவருக்கு நீங்கள் கூறும் மிக முக்கியமான ஆலோசனை என்ன“?!
இந்தக் கேள்விக்கான மறுமொழியை பல வழிகளில் கூறலாம்…
சொந்தமாக தொழில் என்றவுடன் எம் கண்ணுக்கு வருவது ஒரு பலசரக்கு கடை அல்லது வீட்டில் வைத்து செய்யும் ஏதேனும் ஒரு தயாரிப்பு… ஆனால் இன்றைய உலகில் சொந்த தொழில் என்பது மிகவும் பரந்த பல்வேறு துறைகளை உள்ளடக்கியது. ஒரு நூலில் நான் படித்தது ஆனால் மிகவும் சரி என்று எனக்கு பட்டது, நான் படித்திருந்தது உங்களுக்கு உதவலாம்..
அந்த நூலின் ஒவ்வொரு பக்கங்களும் தொழிலின் தோல்வியைப் பற்றி மட்டுமே
பேசுகின்றன.. இந்த உலகில் மனிதன் தொடங்கும் ஒவ்வொரு தொழிலும் தோல்வியிலேயே
முடிகிறது என்று அந்த நூல் சொல்கிறது… எவ்வளவு நாட்கள் கழித்து அந்த தொழில்
தோல்வியில் முடிகிறது என்பதே அந்த தொழிலின் வெற்றியாகும்..
சமீபத்தில் அமேசான் நிறுவனத்தின் நிறுவனர் அளித்த பேட்டி ஒன்றை நான் காண
நேரிட்டது.. அதில் அவர் உறுதியாகச் சொல்கிறார் அமேசான் ஒரு நாளில்
தோல்வியில் முடியும் என்று!! இதன் போது என் கண்முன்னே வந்துபோன காட்சி
Ceylinco House(Ceylinco Consolidated) நிறுவனமும் அதன் உரிமையாளர் Lalith
Kotelawala அவர்களும்தான். இதிலிருந்து நேரடியாகவோ அல்லது
மறைமுகமாகவோ நான் கற்றுக்கொண்ட ஒரு செய்தி என்னவென்றால் நான் செய்யப்போகும்
எந்த ஒரு தொழிலும் இறுதியில் தோல்வியில் முடியப்போகிறது. அதை ஏன்
மிகப்பெரிய தொழிலாக செய்து என்றோ ஒரு நாள் பெரிய தோல்வியை நோக்கி என்
தொழிலை நடத்த கூடாது.…. ________________________________________________
ஒரு இடத்தில் சின்ன பெட்டிக்கடை வைக்க முயற்சி/ முடிவு செய்துவிட்டால் ஒரே
ஒரு பெட்டிக்கடை மட்டும் வைக்காதீர்கள். குறைந்தபட்சம் 5 அல்லது 6
பெட்டிக்கடைகளை ஒரே வரிசையில் வையுங்கள்.. ஒரு பெட்டிக் கடைக்கு தான்
விளம்பரம் என்றும் ஒரே இடத்தில் 5 பெட்டிகடைகள் இருந்தால் மக்கள் தன்னை
அறியாமல் அந்த இடத்தை நோக்கி நகர்வார்கள். . எடுத்துக்காட்டாக BBK, BDP, RENO, MobiFlip மற்றும் OPPO ஒரே நிறுவனத்தின்(Oppo Electronics) அலைபேசி.. Lenova, Medion Motorola, BLADE, ShenQi, Quantum மற்றும் Stoneware ஒரே நிறுவனத்தின் தலைமை நிறுவனமாக கொண்டவை.
நீங்கள் WhatsUp பயன்படுத்தினாலும் அல்லது பேஸ்புக்கின் Messangerரை
பயன்படுத்தினாலும் நீங்கள் சுற்றி சுற்றி ஒரே நிறுவனத்தின் பொருளையே
பயன்படுத்துவதற்கு பழக்கப்படுத்தப்படுகிறீர்கள். _____________________________________________ வேறுபட்ட ஒரு தொழிலை தேர்ந்தெடுங்கள். இந்தத் தொழில் மக்களுக்கு இருக்கும் ஏதேனும் ஒரு சிக்கலைத் தீர்க்க இருக்க வேண்டும்.. அதாவது இன்னொரு விதத்தில் சொல்லப்போனால் நீங்கள் காட்டாத வரை மக்களுக்கு என்ன வேண்டும் என்று அவர்களுக்கே தெரியாது.
எனவே கூடுமானவரை இதுவரை அங்கு கிடைக்காத பொருளை அங்கு விற்கவே படாத பொருளை
விற்க முயற்சி செய்யுங்கள் அது உறுதியாக விற்கும்.. ஏனென்றால் மக்கள்
ஏற்கனவே கிடைக்கும் பொருளை பார்த்து வெறுப்படைந்து விட்டார்கள்.. எவ்வளவுதான் இட்லியும் தோசையும் சத்துள்ள உணவு என்றாலும் அதன் மீதும் ஒரு நாள் நமக்கு வெறுப்பை வரவே செய்கிறது
இப்படி மேலைநாடுகளில் அவர்களின் உணவுப் பழக்கத்தின் மீது ஏற்பட்ட வெறுப்பு
புதிதாக உணவு முறைகளை கண்டு பிடிக்கச் செய்தது… அப்படி வந்ததுதான் இந்த
Pizza, Burger, Cock, Fanta மற்றும் பல… _________________________________________ நீங்கள் வலிமை உள்ளவராக மாறுவதற்கான ஒரே வழி அடுத்தவருக்கு உதவி செய்வது மட்டுமே ஆகும்…இதுதான் எனது வளர்ச்சியின் சூத்திரம்!! உங்களைப் போன்றே தொழில் செய்ய முயலும் உங்கள் பகுதியில் உள்ள சிறு-குறு சேவை வழங்குபவர்களை ஒன்று சேர்க்க முயலுங்கள்…
உதாரணமாக விவசாயம், ஏற்றுமதி தொழிலில் விளங்கும் தொழிலாளர்களை ஒரு செயலி
கொண்டு வந்து அதன் மூலம் அவர்களுக்கு அதிகமான தொழிலை பெற உதவுங்கள்.. இது ஒரு எடுத்துக்காட்டு மட்டுமே இதுபோன்று ஒவ்வொரு தொழிலும் உங்களால் ஒருங்கிணைக்கப்பட்டு பலரும் பலன்களை பெறலாம்… ________________________ வேலையை அனுபவித்து அதற்கு இலக்கு வைத்து செயல்படுங்கள் என்பதுதான் தொழில்முனைவோர்களுக்கு நான் சொல்ல விரும்புவது.
வேலையை ஈடுபாட்டுடன் செயல்பட்டால், பணம் புகழ் என அனைத்தும்
கிடைத்துவிடும். ஆனால் பணத்தை இலக்காக கொண்டு செயல்பட தொடங்கினால், நீங்கள்
நினைத்த பணம் கிடைத்த பிறகு உங்களுக்கு அந்த தொழில் மீது ஆர்வம்,
நம்பிக்கை, மரியாதை குறைந்துவிடும். புலோலியூரான்/யோகீசன்
