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An important operation characteristic of any transport facility including the
multi lane highways is the concept of capacity.
Capacity may be defined as the maximum sustainable flow rate at which vehicles
or persons reasonably can be expected to traverse a point or uniform segment of
a lane or roadway during a specified time period under given roadway, traffic,
environmental, and control conditions; usually expressed as vehicles per hour,
passenger cars per hour, or persons per hour.
There are two types of capacity, possible capacity and practical capacity.
Possible capacity is defined as the maximum number of vehicles that can pass a
point in one hour under prevailing roadway and traffic condition.
Practical capacity on the other hand is the maximum number that can pass the
point without unreasonable delay restriction to the average driver's freedom to
pass other vehicles.
Procedure for computing practical capacity for the uninterrupted
flow condition is as follows:
- Select an operating speed which is acceptable for the class of highways
the terrain and the driver.
- Determine the appropriate capacity for ideal conditions from table 1.
- Determine the reduction factor for conditions which reduce capacity
(such as width of road, alignment, sight distance, heavy vehicle adjustment
factor).
- Multiply these factors by ideal capacity value obtained from step 2.
Table 1:
Free flow speed and capacity for Multilane highway
| Types of facility |
Free flow |
Capacity |
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speed(kmph) |
(pcphpl) |
| Multilane |
100 |
2200 |
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90 |
2100 |
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80 |
2000 |
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70 |
1900 |
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