TRANSPORTATION | CHAPTER 4
TRAFFIC CAPACITY ANALYSIS (LOS)
A capacity analysis compares the actual traffic volumes on a street segment (average per day) with the design capacity of that segment. The ratio of volume over capacity (V/C) cor- responds to a “level of service” (LOS) rating, which provides a rough qualitative measure of speed and smoothness of traffic flow. LOS categories are described as follows:
• LOS A: Free-flowing operation. Vehicles face few impediments to maneuvering. The driver has a high level of physical and psychological comfort. Minor accidents or breakdowns cause little interruption in the traffic stream. LOS A corresponds to a volume-capacity (V/C) score of 0 to 0.60.
• LOS B: A reasonably free-flowing operation. Maneuvering ability is slightly restricted, but ease of movement remains high. LOS B corresponds to a V/C score of 0.60 to 0.70.
• LOS C: Stable operation. Traffic flows approach the range in which traffic increases will degrade service. Minor incidents can be absorbed, but a local slowdown will re- sult. LOS C corresponds to a V/C score of 0.70 to 0.80.
• LOS D: Borders on unstable traffic flow. Small traffic increases produce substantial service deterioration. Maneuverability is limited and comfort reduced. LOS D corre- sponds to a V/C score of 0.80 to 0.90.
• LOS E: Traffic is at full design capacity of street. Operations are extremely unstable because there is little margin of error in the traffic stream. LOS E corresponds to a V/C score of 0.90 to 1.00.
• LOS F: A breakdown in the system. Such conditions exist when queues form behind a breakdown or congestion point. This condition occurs when traffic exceeds the design capacity of the street. LOS F corresponds to a V/C score of above 1.0.
Table 4.1 presents the capacity of various street sections. Streets approaching this capacity may become unstable, while streets over this capacity will likely experi- ence system breakdown. These capacity numbers are provided by HDR, Inc., a na- tional consulting firm specializing in transportation. The analysis in Table 4.2 will compare traffic levels on Cedar Falls streets to these identified capacities to deter- mine existing deficiencies.
Table 4.1: Typi c al Traf f ic Capac i ty by Fac i l i ty Type 2-Lane
Minimal Access Residential
Mixed Zoning Central Business District Source: HDR, Inc., RDG Planning & Design
12,500 12,300 11,200 9,400
3-Lane 16,550
16,250 14,850 12,650
4-Lane 25,400
25,300 23,600 20,500
5-Lane 27,580
27,080 24,750 21,080
6-Lane 38,100
37,950 35,400 30,750
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