The document discusses highway capacity and levels of service, defining basic capacity, possible capacity, and practical capacity as ways to quantify how many vehicles can pass through a given point on a road. It also explains that levels of service, denoted by letters A through F, are used to qualitatively assess traffic flow conditions and driver experience, from free-flowing traffic at level A to forced flow and stop-and-go traffic at level F. Key factors influencing capacity and levels of service include traffic volume, road geometry, and traffic control measures.

1. Established as per the Section 2(f) of the UGC Act, 1956
Approved by AICTE, COA and BCI, New Delhi
Highway capacity and levels of service
School of C i v i l E n g i n e e r i n g
20/06/2020
D r . S e e l a m S r i k a n t h R e d d y
Unit 3

2. HIGHWAY CAPACITY AND LEVELS OF
SERVICE
• Often it is required to find out how much a transport facility can
accommodate?
•Capacity analysis helps in answering the question. It is a quantitative
assessment of the ability of a transport facility to handle vehicles or people for
which it is designed.
•Such information is useful in the design of traffic facility.

3. HIGHWAY CAPACITY AND LEVELS OF
SERVICE
•A related question is, what is the performance level of the system at various
operating conditions. Or in other words, how good is the operation of the
traffic facility.
•Level of Service analysis tries to answer this question which is essentially a
qualitative analysis.

4. HIGHWAY CAPACITY
Basic Capacity: The basic capacity is the maximum number of vehicles that
can pass a given point on a lane or a roadway during one hour under the
most ideal roadway and traffic conditions that can possibly be attained.
Possible Capacity: The possible capacity is the maximum number of vehicles
that can pass a given point on a lane or a roadway during one hour under the
prevailing roadway and traffic conditions.

5. HIGHWAY CAPACITY
Practical Capacity:
• Practical capacity is the maximum number of vehicles that can pass a
given point in a lane or roadway during one hour, when traffic density is
not so great as to cause unreasonable delay, hazard or restriction to the
driver’s freedom to manoeuvre under prevailing roadway and traffic
conditions. This is usually considered to be the ‘design capacity

6. FACTORS INFLUENCING THE HIGHWAY
CAPACITY
•Traffic conditions (vehicle composition, turning movements, etc. )
•Roadway conditions (geometrical characteristics such as lane width, shoulder
width, horizontal alignment, and vertical alignment. )
•Control conditions (traffic signal timings, round-about characteristics etc.)

7. LEVELS OF SERVICE
Level-of-Service is introduced by HCM to denote the level of quality one can
derive from a road under different operational conditions and traffic
volume.
The level of service is defined as a qualitative measure describing the
operational conditions within traffic stream and their perception by drivers
(motorists) and passengers.
Factors in evaluating LoS:
• Speed and travel time
• Traffic interruptions or restrictions
• Freedom to manoeuvre
• Driving comfort and convenience
• Economy

8. LEVELS OF SERVICE
i) Travel speed ii) V/C ratio
Six LOS letters are defined by HCM, namely A, B, C, D, E, and F, where A
denote the best quality of service and F denote the worst.
Level of Service A:
• Free flow, with low volumes and high speeds.
• Traffic density is low, with speeds controlled by drivers desired speed
limits and physical roadway conditions.
• Little or no restriction in manoeuvrability due to presence of other
vehicles.

9. LEVELS OF SERVICE
Level of Service B:
• Zone of stable flow, with operating speeds beginning to be
restricted somewhat by traffic conditions.
• Drivers still have reasonable freedom to select their speed and
lane of operation
• This level of service used in the design of rural highways

10. LEVELS OF SERVICE
Level of Service C:
• Still in the Zone of stable flow, but speeds and manoeuvrability
are controlled by higher volumes.
• Most of Drivers restricted in the freedom to select their own
speed and lane changing or overtaking.
• This level of service used in the urban design practice

11. LEVELS OF SERVICE
Level of Service D:
• Approaches unstable flow, with operating speeds considerably
affected by changes in operating conditions.
• Drivers have little freedom to manoeuvre comfort and
convenience are low, but conditions can be tolerated for short
periods of time.

12. LEVELS OF SERVICE
Level of Service E:
• Flow is unstable, and there may be stoppages of momentary
duration.
• Can described by speed alone, but represents with lower
operating speeds than in level D and with volumes at or near
the capacity of the highway.

13. LEVELS OF SERVICE
Level of Service F:
• Forced flow conditions at lower speeds, where volumes are just
below capacity.
• Speeds are reduced substantially and stoppage may occur for
short or long periods of time because of congestion.
• In the extreme, both speed and volume can drop to zero

14. LEVELS OF SERVICE