You cannot fix a problem you have not measured. Before any road is widened, any signal installed, or any bypass planned, somebody has to go out and count what is actually happening — how many vehicles, how fast, going where, stopping when.
That measuring work is called traffic studies, and this post covers all seven types, what each one answers, and why they exist.
What Traffic Studies Are
Traffic surveys carried out to collect traffic data are also known as a traffic census.
The word census is well chosen. A population census counts people to plan schools and hospitals. A traffic census counts vehicles to plan roads and signals. Both are systematic head-counts done so that public money is spent where it is actually needed.
Why They Are Done
These studies help in deciding the geometric design features and the traffic control measures needed for safe and efficient traffic movement.
Two distinct outputs, and it is worth separating them:
- Geometric design features — the physical road. How many lanes, how wide, what curve radii, what gradients.
- Traffic control — the operating rules. Where signals go, what the timings should be, which streets become one-way, where signs and markings belong.
The first costs a great deal and lasts decades. The second is comparatively cheap and can be changed. Good traffic data helps you decide which of the two your problem actually needs — and a surprising number of congestion problems turn out to be control problems, not width problems.
The Seven Types of Traffic Study
| Study | The Question It Answers |
|---|---|
| (a) Traffic volume study | How many vehicles? |
| (b) Speed studies — spot speed study and speed and delay study | How fast, and where are they held up? |
| (c) Origin and destination (O & D) study | Where are they coming from and going to? |
| (d) Traffic flow characteristics | How do speed, volume and density relate to each other? |
| (e) Traffic capacity study | How many vehicles can this road actually take? |
| (f) Parking study | Where do vehicles stop, and is there room? |
| (g) Accident studies | Where and why are crashes happening? |
Notice that speed studies are listed as a single item but split into two sub-types, because they answer genuinely different questions.
Looking at Each in Turn
(a) Traffic Volume Study
The most basic study of all — a count of vehicles crossing a section of road per unit time. Volume tells you how important a road is relative to others, and it feeds directly into capacity calculations and pavement design.
(b) Speed Studies
Two distinct kinds:
- Spot speed study measures the instantaneous speed of vehicles at one particular location. It tells you how fast traffic moves at that point, which is what you need for setting speed limits and designing curves and signals.
- Speed and delay study follows vehicles over a stretch of road. It tells you not just the speed but where and why vehicles are being held up.
The distinction matters because a spot speed study, being confined to a single point, cannot give traffic density. Density is vehicles per kilometre, and measuring it requires observing a length of road, not a point.
(c) Origin and Destination Study
Volume tells you how many vehicles pass a point. It says nothing about where they came from or where they are heading. An O & D study answers that — and the answer determines whether a town needs a bypass, a new link road, or simply better signals.
If most vehicles passing through a congested market town are merely travelling through it, a bypass solves the problem. If most are stopping there, a bypass helps nobody and the money should go elsewhere. Only an O & D study can tell you which situation you are in.
(d) Traffic Flow Characteristics
This study examines the relationships between the three fundamental quantities — speed, volume and density. These are not independent; changing one changes the others, and understanding those relationships underlies all capacity analysis.
(e) Traffic Capacity Study
Capacity is the maximum number of vehicles a road can handle. Volume tells you what is currently using the road; capacity tells you what the road could take. Comparing the two tells you whether the road is comfortably underused, working near its limit, or already overwhelmed.
(f) Parking Study
A vehicle spends most of its life stationary, and every stationary vehicle occupies space that must come from somewhere. Parking studies examine demand, existing characteristics and available space, and they matter enormously in urban areas where kerbside parking eats directly into carriageway width.
(g) Accident Studies
The most important study of all, because it deals with harm that has already occurred. Systematic accident studies investigate causes so that safety measures — engineering, enforcement or education — can be directed where they will do the most good.
Means of Conducting Traffic Surveys
Traffic surveys can be conducted through a range of methods:
- Toll plaza ticketing — every vehicle is already being recorded as it pays
- Registration offices — records of vehicles registered in an area
- Statistical approach — sampling and extrapolation rather than complete enumeration
- Interview — asking road users directly
- Check post — recording vehicles at fixed control points
- Modern Global Positioning studies — using GPS tracking data
The older methods count vehicles at fixed points. GPS-based methods do something fundamentally different — they follow individual vehicles continuously, which yields origin, destination, route choice and delay from a single data source.
How the Studies Fit Together
Each study answers one question, and together they build a complete picture:
Volume tells you how much → Speed tells you how fast → O & D tells you where to and from → Capacity tells you how much more is possible → Parking tells you where they stop → Accidents tell you what is going wrong
No single study is sufficient on its own. A road with low volume but a poor accident record needs safety work, not widening. A road at capacity but with mostly through traffic needs a bypass, not more lanes. The studies only become useful when read together.
Quick Revision Notes
- Traffic surveys for collecting traffic data are also called a traffic census.
- They help decide geometric design features and traffic control measures.
- Seven types: traffic volume, speed studies, origin and destination, traffic flow characteristics, traffic capacity, parking, accident studies.
- Speed studies divide into spot speed study and speed and delay study.
- Spot speed studies cannot determine density, because they observe a single point only.
- Survey methods: toll plaza ticketing, registration offices, statistical approach, interview, check post, GPS studies.
Mistakes Students Commonly Make
- Listing spot speed study and speed and delay study as separate main types. Both fall under speed studies.
- Forgetting traffic flow characteristics, which is easy to overlook because it sounds like a general heading rather than a specific study.
- Confusing volume with capacity. Volume is what is happening; capacity is what is possible.
- Assuming a spot speed study can yield density. It cannot — density needs observation over a length.
- Treating traffic census as something different from traffic surveys. They are the same thing.
Conclusion
Traffic studies are the measurement stage that every traffic engineering decision rests on. Seven types, each answering one question — how many, how fast, where from and to, how the flow behaves, how much the road can take, where vehicles park, and where crashes happen. Learn the list, learn which question each study answers, and remember that the right remedy for a congested road depends entirely on which of these questions turns out to be the problem.
Frequently Asked Questions
What are traffic studies?
Surveys carried out to collect traffic data, also known as a traffic census. They help decide geometric design features and traffic control measures for safe and efficient traffic movement.
What is another name for traffic surveys?
Traffic census.
What are the seven types of traffic study?
Traffic volume study, speed studies, origin and destination study, traffic flow characteristics, traffic capacity study, parking study and accident studies.
What are the two types of speed study?
Spot speed study, which measures speed at a single location, and speed and delay study, which follows vehicles over a length of road.
Why can a spot speed study not measure density?
Because density is the number of vehicles per kilometre, which requires observing a length of road. A spot speed study takes measurements at one point only.
What methods are used to conduct traffic surveys?
Toll plaza ticketing, registration offices, statistical approaches, interviews, check posts and modern Global Positioning studies.
Why is an origin and destination study needed if volume is already known?
Because volume only counts vehicles passing a point. It cannot tell you whether that traffic is passing through or stopping locally, which is what decides whether a bypass would help.