Capacity analyses allow traffic engineers to determine the impacts of traffic on the surrounding roadway network. The Transportation Research Board's (TRB) Highway Capacity Manual (HCM) methodologies govern how the capacity analyses are conducted and how the results are interpreted. There are six letter grades of Levels of Service (LOS) from A to F, with LOS A representing the best operating conditions and LOS F representing the worst operating conditions.
For signalized and unsignalized intersections, LOS is defined in terms of delay, a measure of driver discomfort, frustration, fuel consumption, and lost travel time. Table 6-1 summarizes the delay associated with each LOS category:
Table 6-1: Level of Service Criteria
| Signalized Intersections | Unsignalized Intersections |
| Level of Service | Control Delay per Vehicle (sec/veh) | Level of Service | Average Control Delay (sec/veh) |
|---|
| A | ≤ 10 | A | 0 to 10 |
|---|
| B | > 10 to ≤ 20 | B | > 10 to ≤ 15 |
|---|
| C | > 20 to ≤ 35 | C | > 15 to ≤ 25 |
|---|
| D | > 35 to ≤ 55 | D | > 25 to ≤ 35 |
|---|
| E | > 55 to ≤ 80 | E | > 35 to ≤ 50 |
|---|
| F | > 80 | F | > 50 |
|---|
Generally, the standard acceptable minimum for the overall intersection is LOS D, while the standard acceptable minimum for an individual traffic movement is LOS E.
I he Chicago Avenue and Waterman Drive corridor was analyzed using both the existing geometry and with proposed intersection improvements. The intersections were analyzed using SYNCHRO based on Highway Capacity Manual 2000 methodologies. Capacity analysis was performed with the following assumptions:
Level terrain;
12-foot lane widths;
No parking activity or bus stops;
Existing peak-hour factor as determined by the traffic counts (by intersection) for existing scenario;
6-2